Central nervous system cerebrum: What Is Central Nervous System? Definition, Function & Parts
What Is Central Nervous System? Definition, Function & Parts
Peripheral Nervous System Function
Nerve fibers that exit the brainstem and spinal cord become part of the peripheral nervous system. Cranial nerves exit the brainstem and function as peripheral nervous system mediators of many functions, including eye movements, facial strength and sensation, hearing, and taste.
The optic nerve is considered a cranial nerve but it is generally affected in a disease of the central nervous system known as multiple sclerosis, and, for this and other reasons, it is thought to represent an extension of the central nervous system apparatus that controls vision. In fact, doctors can diagnose inflammation of the head of the optic nerve by using an ophthalmoscope, as if the person’s eyes were a window into the central nervous system.
Nerve roots leave the spinal cord to the exit point between two vertebrae and are named according to the spinal cord segment from which they arise (a cervical eight nerve root arises from cervical spinal cord segment eight). Nerve roots are located anterior with relation to the cord if efferent (for example, carrying input toward limbs) or posterior if afferent (for example, to spinal cord).
Fibers that carry motor input to limbs and fibers that bring sensory information from the limbs to the spinal cord grow together to form a mixed (motor and sensory) peripheral nerve. Some lumbar and all sacral nerve roots take a long route downward in the spinal canal before they exit in a bundle that resembles a horse’s tail, hence its name, cauda equina.
The spinal cord is also covered, like the brain, by the pia matter and the arachnoid membranes. The cerebrospinal fluid circulates around the pia and below the outer arachnoid, and this space is also termed the subarachnoid space. The roots of the cauda equina and the rootlets that make up the nerve roots from higher segments are bathed in cerebrospinal fluid. The dura surrounds the pia-arachnoid of the spinal cord, as it does for the brain.
The neuroanatomical basis for multiple brain functions is oversimplified in the above summary. A good example is the neuroanatomical substrate for memory function. Damage to multiple areas of the brain can affect memory. These include structures such as the frontal and temporal lobes, the thalamus, the cerebellum, the putamen, mamillary bodies and fornix, and a convolution above the corpus callosum known as the cingulate gyrus. These structures are variably involved in complex processes such as the storing, processing, or retrieval of memories.
Central Nervous System: brain and spinal cord – Queensland Brain Institute
Our bodies couldn’t operate without the nervous system – the complex network that coordinates our actions, reflexes, and sensations. Broadly speaking, the nervous system is organised into two main parts, the central nervous system (CNS) and the peripheral nervous system (PNS).
The CNS is the processing centre of the body and consists of the brain and the spinal cord. Both of these are protected by three layers of membranes known as meninges. For further protection, the brain is encased within the hard bones of the skull, while the spinal cord is protected with the bony vertebrae of our backbones. A third form of protection is cerebrospinal fluid, which provides a buffer that limits impact between the brain and skull or between spinal cord and vertebrae.
Grey and white matter
In terms of tissue, the CNS is divided into grey matter and white matter. Grey matter comprises neuron cell bodies and their dendrites, glial cells, and capillaries. Because of the abundant blood supply of this tissue, it’s actually more pink-coloured than grey.
In the brain, grey matter is mainly found in the outer layers, while in the spinal cord it forms the core ‘butterfly’ shape.
White matter refers to the areas of the CNS which host the majority of axons, the long cords that extend from neurons. Most axons are coated in myelin – a white, fatty insulating cover that helps nerve signals travel quickly and reliably. In the brain, white matter is buried under the grey surface, carrying signals across different parts of the brain. In the spinal cord, white matter is the external layer surrounding the grey core.
The brain
Image: QBI/Levent Efe
If the CNS is the processing centre of the human body, the brain is its headquarters. It is broadly organised into three main regions – the forebrain, the midbrain, and the hindbrain. The largest of these three is the forebrain (derived from the prosencephalon in the developing brain). It contains the large outermost layer of the brain, the wrinkly cerebral cortex, and smaller structures towards its centre, such as the thalamus, hypothalamus, and the pineal gland.
The midbrain (derived from the mesencephalon in the developing brain) serves as the vital connection point between the forebrain and the hindbrain. It’s the top part of the brainstem, which connects the brain to the spinal cord.
The hindbrain (derived from the rhombencephalon in the developing brain) is the lowest back portion of the brain, containing the rest of the brainstem made up of medulla oblongata and the pons, and also the cerebellum – a small ball of dense brain tissue nestled right against the back of the brainstem.
Parts of the brain
The brain’s cerebral cortex is the outermost layer that gives the brain its characteristic wrinkly appearance. The cerebral cortex is divided lengthways into two cerebral hemispheres, each of which traditionally have been divided into four lobes: frontal, parietal, temporal and occipital. Read more.
Central nervous system: Structure, function, and diseases
The central nervous system consists of the brain and spinal cord. It is referred to as “central” because it combines information from the entire body and coordinates activity across the whole organism.
This article gives a brief overview of the central nervous system (CNS). We will look at the types of cells involved, different regions within the brain, spinal circuitry, and how the CNS can be affected by disease and injury.
The CNS consists of the brain and spinal cord.
The brain is protected by the skull (the cranial cavity) and the spinal cord travels from the back of the brain, down the center of the spine, stopping in the lumbar region of the lower back.
The brain and spinal cord are both housed within a protective triple-layered membrane called the meninges.
The central nervous system has been thoroughly studied by anatomists and physiologists, but it still holds many secrets; it controls our thoughts, movements, emotions, and desires. It also controls our breathing, heart rate, the release of some hormones, body temperature, and much more.
The retina, optic nerve, olfactory nerves, and olfactory epithelium are sometimes considered to be part of the CNS alongside the brain and spinal cord. This is because they connect directly with brain tissue without intermediate nerve fibers.
Below is a 3D map of the CMS. Click on it to interact and explore the model.
Now we will look at some of the parts of the CNS in more detail, starting with the brain.
The brain is the most complex organ in the human body; the cerebral cortex (the outermost part of the brain and the largest part by volume) contains an estimated 15–33 billion neurons, each of which is connected to thousands of other neurons.
In total, around 100 billion neurons and 1,000 billion glial (support) cells make up the human brain. Our brain uses around 20 percent of our body’s total energy.
The brain is the central control module of the body and coordinates activity. From physical motion to the secretion of hormones, the creation of memories, and the sensation of emotion.
To carry out these functions, some sections of the brain have dedicated roles. However, many higher functions — reasoning, problem-solving, creativity — involve different areas working together in networks.
The brain is roughly split into four lobes:
Temporal lobe (green): important for processing sensory input and assigning it emotional meaning.
It is also involved in laying down long-term memories. Some aspects of language perception are also housed here.
Occipital lobe (purple): visual processing region of the brain, housing the visual cortex.
Parietal lobe (yellow): the parietal lobe integrates sensory information including touch, spatial awareness, and navigation.
Touch stimulation from the skin is ultimately sent to the parietal lobe. It also plays a part in language processing.
Frontal lobe (pink): positioned at the front of the brain, the frontal lobe contains the majority of dopamine-sensitive neurons and is involved in attention, reward, short-term memory, motivation, and planning.
Brain regions
Next, we will look at some specific brain regions in a little more detail:
Basal ganglia: involved in the control of voluntary motor movements, procedural learning, and decisions about which motor activities to carry out. Diseases that affect this area include Parkinson’s disease and Huntington’s disease.
Cerebellum: mostly involved in precise motor control, but also in language and attention. If the cerebellum is damaged, the primary symptom is disrupted motor control, known as ataxia.
Broca’s area: this small area on the left side of the brain (sometimes on the right in left-handed individuals) is important in language processing. When damaged, an individual finds it difficult to speak but can still understand speech. Stuttering is sometimes associated with an underactive Broca’s area.
Corpus callosum: a broad band of nerve fibers that join the left and right hemispheres. It is the largest white matter structure in the brain and allows the two hemispheres to communicate. Dyslexic children have smaller corpus callosums; left-handed people, ambidextrous people, and musicians typically have larger ones.
Medulla oblongata: extending below the skull, it is involved in involuntary functions, such as vomiting, breathing, sneezing, and maintaining the correct blood pressure.
Hypothalamus: sitting just above the brain stem and roughly the size of an almond, the hypothalamus secretes a number of neurohormones and influences body temperature control, thirst, and hunger.
Thalamus: positioned in the center of the brain, the thalamus receives sensory and motor input and relays it to the rest of the cerebral cortex. It is involved in the regulation of consciousness, sleep, awareness, and alertness.
Amygdala: two almond-shaped nuclei deep within the temporal lobe. They are involved in decision-making, memory, and emotional responses; particularly negative emotions.
Share on PinterestThe spinal cord carries information from the brain to the rest of the body.
The spinal cord, running almost the full length of the back, carries information between the brain and body, but also carries out other tasks.
From the brainstem, where the spinal cord meets the brain, 31 spinal nerves enter the cord.
Along its length, it connects with the nerves of the peripheral nervous system (PNS) that run in from the skin, muscles, and joints.
Motor commands from the brain travel from the spine to the muscles and sensory information travels from the sensory tissues — such as the skin — toward the spinal cord and finally up to the brain.
The spinal cord contains circuits that control certain reflexive responses, such as the involuntary movement your arm might make if your finger was to touch a flame.
The circuits within the spine can also generate more complex movements such as walking. Even without input from the brain, the spinal nerves can coordinate all of the muscles necessary to walk. For instance, if the brain of a cat is separated from its spine so that its brain has no contact with its body, it will start spontaneously walking when placed on a treadmill. The brain is only required to stop and start the process, or make changes if, for instance, an object appears in your path.
The CNS can be roughly divided into white and gray matter. As a very general rule, the brain consists of an outer cortex of gray matter and an inner area housing tracts of white matter.
Both types of tissue contain glial cells, which protect and support neurons. White matter mostly consists of axons (nerve projections) and oligodendrocytes — a type of glial cell — whereas gray matter consists predominantly of neurons.
Also called neuroglia, glial cells are often called support cells for neurons. In the brain, they outnumber nerve cells 10 to 1.
Without glial cells, developing nerves often lose their way and struggle to form functioning synapses.
Glial cells are found in both the CNS and PNS but each system has different types. The following are brief descriptions of the CNS glial cell types:
Astrocytes: these cells have numerous projections and anchor neurons to their blood supply. They also regulate the local environment by removing excess ions and recycling neurotransmitters.
Oligodendrocytes: responsible for creating the myelin sheath — this thin layer coats nerve cells, allowing them to send signals quickly and efficiently.
Ependymal cells: lining the spinal cord and the brain’s ventricles (fluid-filled spaces), these create and secrete cerebrospinal fluid (CSF) and keep it circulating using their whip-like cilia.
Radial glia: act as scaffolding for new nerve cells during the creation of the embryo’s nervous system.
The cranial nerves are 12 pairs of nerves that arise directly from the brain and pass through holes in the skull rather than traveling along the spinal cord. These nerves collect and send information between the brain and parts of the body – mostly the neck and head.
Of these 12 pairs, the olfactory and optic nerves arise from the forebrain and are considered part of the central nervous system:
Olfactory nerves (cranial nerve I): transmit information about odors from the upper section of the nasal cavity to the olfactory bulbs on the base of the brain.
Optic nerves (cranial nerve II): carry visual information from the retina to the primary visual nuclei of the brain. Each optic nerve consists of around 1.7 million nerve fibers.
Below are the major causes of disorders that affect the CNS:
Trauma: depending on the site of the injury, symptoms can vary widely from paralysis to mood disorders.
Infections: some micro-organisms and viruses can invade the CNS; these include fungi, such as cryptococcal meningitis; protozoa, including malaria; bacteria, as is the case with leprosy, or viruses.
Degeneration: in some cases, the spinal cord or brain can degenerate. One example is Parkinson’s disease which involves the gradual degeneration of dopamine-producing cells in the basal ganglia.
Structural defects: the most common examples are birth defects; including anencephaly, where parts of the skull, brain, and scalp are missing at birth.
Tumors: both cancerous and noncancerous tumors can impact parts of the central nervous system. Both types can cause damage and yield an array of symptoms depending on where they develop.
Autoimmune disorders: in some cases, an individual’s immune system can mount an attack on healthy cells. For instance, acute disseminated encephalomyelitis is characterized by an immune response against the brain and spinal cord, attacking myelin (the nerves’ insulation) and, therefore, destroying white matter.
Stroke: a stroke is an interruption of blood supply to the brain; the resulting lack of oxygen causes tissue to die in the affected area.
Difference between the CNS and peripheral nervous system
The term peripheral nervous system (PNS) refers to any part of the nervous system that lies outside of the brain and spinal cord. The CNS is separate from the peripheral nervous system, although the two systems are interconnected.
There are a number of differences between the CNS and PNS; one difference is the size of the cells. The nerve axons of the CNS — the slender projections of nerve cells that carry impulses — are much shorter. PNS nerve axons can be up to 1 meter long (for instance, the nerve that activates the big toe) whereas, within the CNS, they are rarely longer than a few millimeters.
Another major difference between the CNS and PNS involves regeneration (regrowth of cells). Much of the PNS has the ability to regenerate; if a nerve in your finger is severed, it can regrow. The CNS, however, does not have this ability.
The components of the central nervous system are further split into a myriad of parts. Below, we will describe some of these sections in a little more detail.
Central nervous system: Structure, function, and diseases
The central nervous system consists of the brain and spinal cord. It is referred to as “central” because it combines information from the entire body and coordinates activity across the whole organism.
This article gives a brief overview of the central nervous system (CNS). We will look at the types of cells involved, different regions within the brain, spinal circuitry, and how the CNS can be affected by disease and injury.
The CNS consists of the brain and spinal cord.
The brain is protected by the skull (the cranial cavity) and the spinal cord travels from the back of the brain, down the center of the spine, stopping in the lumbar region of the lower back.
The brain and spinal cord are both housed within a protective triple-layered membrane called the meninges.
The central nervous system has been thoroughly studied by anatomists and physiologists, but it still holds many secrets; it controls our thoughts, movements, emotions, and desires. It also controls our breathing, heart rate, the release of some hormones, body temperature, and much more.
The retina, optic nerve, olfactory nerves, and olfactory epithelium are sometimes considered to be part of the CNS alongside the brain and spinal cord. This is because they connect directly with brain tissue without intermediate nerve fibers.
Below is a 3D map of the CMS. Click on it to interact and explore the model.
Now we will look at some of the parts of the CNS in more detail, starting with the brain.
The brain is the most complex organ in the human body; the cerebral cortex (the outermost part of the brain and the largest part by volume) contains an estimated 15–33 billion neurons, each of which is connected to thousands of other neurons.
In total, around 100 billion neurons and 1,000 billion glial (support) cells make up the human brain. Our brain uses around 20 percent of our body’s total energy.
The brain is the central control module of the body and coordinates activity. From physical motion to the secretion of hormones, the creation of memories, and the sensation of emotion.
To carry out these functions, some sections of the brain have dedicated roles. However, many higher functions — reasoning, problem-solving, creativity — involve different areas working together in networks.
The brain is roughly split into four lobes:
Temporal lobe (green): important for processing sensory input and assigning it emotional meaning.
It is also involved in laying down long-term memories. Some aspects of language perception are also housed here.
Occipital lobe (purple): visual processing region of the brain, housing the visual cortex.
Parietal lobe (yellow): the parietal lobe integrates sensory information including touch, spatial awareness, and navigation.
Touch stimulation from the skin is ultimately sent to the parietal lobe. It also plays a part in language processing.
Frontal lobe (pink): positioned at the front of the brain, the frontal lobe contains the majority of dopamine-sensitive neurons and is involved in attention, reward, short-term memory, motivation, and planning.
Brain regions
Next, we will look at some specific brain regions in a little more detail:
Basal ganglia: involved in the control of voluntary motor movements, procedural learning, and decisions about which motor activities to carry out. Diseases that affect this area include Parkinson’s disease and Huntington’s disease.
Cerebellum: mostly involved in precise motor control, but also in language and attention. If the cerebellum is damaged, the primary symptom is disrupted motor control, known as ataxia.
Broca’s area: this small area on the left side of the brain (sometimes on the right in left-handed individuals) is important in language processing. When damaged, an individual finds it difficult to speak but can still understand speech. Stuttering is sometimes associated with an underactive Broca’s area.
Corpus callosum: a broad band of nerve fibers that join the left and right hemispheres. It is the largest white matter structure in the brain and allows the two hemispheres to communicate. Dyslexic children have smaller corpus callosums; left-handed people, ambidextrous people, and musicians typically have larger ones.
Medulla oblongata: extending below the skull, it is involved in involuntary functions, such as vomiting, breathing, sneezing, and maintaining the correct blood pressure.
Hypothalamus: sitting just above the brain stem and roughly the size of an almond, the hypothalamus secretes a number of neurohormones and influences body temperature control, thirst, and hunger.
Thalamus: positioned in the center of the brain, the thalamus receives sensory and motor input and relays it to the rest of the cerebral cortex. It is involved in the regulation of consciousness, sleep, awareness, and alertness.
Amygdala: two almond-shaped nuclei deep within the temporal lobe. They are involved in decision-making, memory, and emotional responses; particularly negative emotions.
Share on PinterestThe spinal cord carries information from the brain to the rest of the body.
The spinal cord, running almost the full length of the back, carries information between the brain and body, but also carries out other tasks.
From the brainstem, where the spinal cord meets the brain, 31 spinal nerves enter the cord.
Along its length, it connects with the nerves of the peripheral nervous system (PNS) that run in from the skin, muscles, and joints.
Motor commands from the brain travel from the spine to the muscles and sensory information travels from the sensory tissues — such as the skin — toward the spinal cord and finally up to the brain.
The spinal cord contains circuits that control certain reflexive responses, such as the involuntary movement your arm might make if your finger was to touch a flame.
The circuits within the spine can also generate more complex movements such as walking. Even without input from the brain, the spinal nerves can coordinate all of the muscles necessary to walk. For instance, if the brain of a cat is separated from its spine so that its brain has no contact with its body, it will start spontaneously walking when placed on a treadmill. The brain is only required to stop and start the process, or make changes if, for instance, an object appears in your path.
The CNS can be roughly divided into white and gray matter. As a very general rule, the brain consists of an outer cortex of gray matter and an inner area housing tracts of white matter.
Both types of tissue contain glial cells, which protect and support neurons. White matter mostly consists of axons (nerve projections) and oligodendrocytes — a type of glial cell — whereas gray matter consists predominantly of neurons.
Also called neuroglia, glial cells are often called support cells for neurons. In the brain, they outnumber nerve cells 10 to 1.
Without glial cells, developing nerves often lose their way and struggle to form functioning synapses.
Glial cells are found in both the CNS and PNS but each system has different types. The following are brief descriptions of the CNS glial cell types:
Astrocytes: these cells have numerous projections and anchor neurons to their blood supply. They also regulate the local environment by removing excess ions and recycling neurotransmitters.
Oligodendrocytes: responsible for creating the myelin sheath — this thin layer coats nerve cells, allowing them to send signals quickly and efficiently.
Ependymal cells: lining the spinal cord and the brain’s ventricles (fluid-filled spaces), these create and secrete cerebrospinal fluid (CSF) and keep it circulating using their whip-like cilia.
Radial glia: act as scaffolding for new nerve cells during the creation of the embryo’s nervous system.
The cranial nerves are 12 pairs of nerves that arise directly from the brain and pass through holes in the skull rather than traveling along the spinal cord. These nerves collect and send information between the brain and parts of the body – mostly the neck and head.
Of these 12 pairs, the olfactory and optic nerves arise from the forebrain and are considered part of the central nervous system:
Olfactory nerves (cranial nerve I): transmit information about odors from the upper section of the nasal cavity to the olfactory bulbs on the base of the brain.
Optic nerves (cranial nerve II): carry visual information from the retina to the primary visual nuclei of the brain. Each optic nerve consists of around 1.7 million nerve fibers.
Below are the major causes of disorders that affect the CNS:
Trauma: depending on the site of the injury, symptoms can vary widely from paralysis to mood disorders.
Infections: some micro-organisms and viruses can invade the CNS; these include fungi, such as cryptococcal meningitis; protozoa, including malaria; bacteria, as is the case with leprosy, or viruses.
Degeneration: in some cases, the spinal cord or brain can degenerate. One example is Parkinson’s disease which involves the gradual degeneration of dopamine-producing cells in the basal ganglia.
Structural defects: the most common examples are birth defects; including anencephaly, where parts of the skull, brain, and scalp are missing at birth.
Tumors: both cancerous and noncancerous tumors can impact parts of the central nervous system. Both types can cause damage and yield an array of symptoms depending on where they develop.
Autoimmune disorders: in some cases, an individual’s immune system can mount an attack on healthy cells. For instance, acute disseminated encephalomyelitis is characterized by an immune response against the brain and spinal cord, attacking myelin (the nerves’ insulation) and, therefore, destroying white matter.
Stroke: a stroke is an interruption of blood supply to the brain; the resulting lack of oxygen causes tissue to die in the affected area.
Difference between the CNS and peripheral nervous system
The term peripheral nervous system (PNS) refers to any part of the nervous system that lies outside of the brain and spinal cord. The CNS is separate from the peripheral nervous system, although the two systems are interconnected.
There are a number of differences between the CNS and PNS; one difference is the size of the cells. The nerve axons of the CNS — the slender projections of nerve cells that carry impulses — are much shorter. PNS nerve axons can be up to 1 meter long (for instance, the nerve that activates the big toe) whereas, within the CNS, they are rarely longer than a few millimeters.
Another major difference between the CNS and PNS involves regeneration (regrowth of cells). Much of the PNS has the ability to regenerate; if a nerve in your finger is severed, it can regrow. The CNS, however, does not have this ability.
The components of the central nervous system are further split into a myriad of parts. Below, we will describe some of these sections in a little more detail.
Anatomy, Central Nervous System – StatPearls
Introduction
The nervous system subdivides into the central nervous system and the peripheral nervous system. The central nervous system is the brain and spinal cord, while the peripheral nervous system consists of everything else. The central nervous system’s responsibilities include receiving, processing, and responding to sensory information.
The brain is an organ of nervous tissue that is responsible for responses, sensation, movement, emotions, communication, thought processing, and memory. Protection for the human brain comes from the skull, meninges, and cerebrospinal fluids. The nervous tissue is extremely delicate and can suffer damage by the smallest amount of force. In addition, it has a blood-brain barrier preventing the brain from any harmful substance that could be floating in the blood.
The spinal cord is a vital aspect of the CNS found within the vertebral column. The purpose of the spinal cord is to send motor commands from the brain to the peripheral body as well as to relay sensory information from the sensory organs to the brain. Spinal cord protection is by bone, meninges, and cerebrospinal fluids.
Structure and Function
The brain is broken up into two hemispheres, the left, and the right. While they are in constant communication, the left and right hemisphere are responsible for different behaviors, known as brain lateralization. The left hemisphere is more dominant with language, logic, and math abilities. The right hemisphere is more creative, being dominant in artistic and musical situations, and intuition.
Cerebral cortex: The cerebral cortex is the outermost layer that surrounds the brain. It is composed of gray matter and filled with billions of neurons used to conduct high-level executive functions. The cortex divides into four lobes; frontal, parietal, occipital, and temporal by different sulci.[1] The frontal lobe, located anteriorly to the central sulcus, is responsible for voluntary motor function, problem-solving, attention, memory, and language. Located in the frontal lobe are the motor cortex and the Broca area. The motor cortex allows for the precise voluntary movements of our skeletal muscles, while the Broca area controls motor functions responsible for producing language. The parietal lobe is separated from the occipital lobe by the parieto-occipital sulcus and is behind the central sulcus. It is responsible for processing sensory information and contains the somatosensory cortex. Neurons in the parietal lobe receive information from sensory and proprioceptors throughout the body, process the can, and form an understanding about what is being touched based on previous knowledge. The occipital lobe, known as the visual processing center, contains the visual cortex. Similar to the parietal lobe, the occipital lobe receives information from the retina and then uses past visual experiences to interpret and recognize the stimuli. Lastly, the temporal lobe processes auditory stimuli through the auditory cortex. Mechanoreceptors located in the hair cells lining the cochlea are activated by sound energy, which in turn sends impulses to the auditory cortex. The impulse is processed and stored based on previous experiences. The Wernicke area is in the temporal lobe and functions in speech comprehension.
Basal nuclei: The basal nuclei, also known as basal ganglia, is located deep within the cerebral white matter and is composed of the caudate nucleus, putamen, and globus pallidus. These structures form the pallidum and striatum. The basal ganglia are responsible for muscle movements and coordination.[2]
Thalamus: The thalamus is the relay center of the brain. It receives afferent impulses from sensory receptors located throughout the body and processes the information for distribution to the appropriate cortical area. It is also responsible for regulating consciousness and sleep.
Hypothalamus: While the hypothalamus is one of the smallest parts of the brain, it is vital to maintaining homeostasis. The hypothalamus connects the central nervous system to the endocrine system. It is responsible for heart rate, blood pressure, appetite, thirst, temperature, and the release of various hormones. The hypothalamus also communicates with the pituitary gland to release or inhibit antidiuretic hormone, corticotropin-releasing hormone, gonadotropin-releasing hormone, growth hormone-releasing hormone, prolactin inhibiting hormone, thyroid releasing hormone, and oxytocin.[3]
Pons: Found in the brainstem, the pons connects the medulla oblongata and the thalamus. It is composed of tracts responsible for relaying impulses from the motor cortex to the cerebellum, medulla, and thalamus.
Medulla oblongata: The medulla oblongata is at the bottom of the brain stem, where the spinal cord meets the foramen magnum of the skull. It is responsible for autonomic functions, some of which are crucial for survival. The medulla oblongata monitors the bodies respiratory system using chemoreceptors. These receptors are able to detect changes in blood chemistry. For example, if the blood is too acidic, the medulla oblongata will increase the respiratory rate allowing for more oxygen to reach the blood.[4] It is also a cardiovascular and vasomotor center. The medulla oblongata can regulate the body’s blood pressure, pulse, and cardiac contractions based on the body’s needs. Lastly, it controls reflexes like vomiting, swallowing, coughing, and sneezing.
Cerebellum: The cerebellum, also known as the little brain, is responsible for smooth, coordinated voluntary movements. It subdivides into three lobes: the anterior, posterior, and flocculonodular lobes. The cerebellum contains a cerebellar circuit, using Purkinje cells and cerebellar peduncles to communicate to other parts of the brain. The superior cerebellar peduncle is composed of white matter that connects the cerebellum to the midbrain and allows for coordination in the arms and legs. The inferior cerebellar peduncle connects the medulla and cerebellum using proprioceptors to maintain balance and posture. Lastly, the middle cerebellar peduncle is used as a one-way communication method from the pons to the cerebellum. It is mostly composed of afferent fibers that alert the cerebellum about voluntary motor actions. The cerebellum is in constant communication with the cerebral cortex, taking higher-level instructions about the brain’s intentions, processing them through the cerebellar cortex, then sending messages to the cerebral motor cortex to make voluntary muscle contractions. These contractions are calculated to determine the force, direction, and momentum necessary to ensure each contraction is smooth and coordinated.
Limbic System: The limbic system is composed of the piriform cortex, hippocampus, septal nuclei, amygdala, nucleus accumbens, hypothalamus, and anterior nuclei of the thalamus.[5] The fornix and fiber tracts connect the limbic system parts allowing them to control emotion, memory, and motivation. The piriform cortex is part of the olfactory system and is in the cortical area of the limbic system. The hypothalamus receives most of the limbic output, which explains psychosomatic illnesses, where emotional stressors cause somatic symptoms. For example, a patient who is currently having financial struggles might present to his primary care physician with hypertension and tachycardia. The septal nuclei, amygdala, and nucleus accumbens are found in the subcortical areas and are responsible for pleasure, emotional processing, and addiction, respectively.
Reticular formation: Reticular formation is an extensive network of pathways containing neurons that begins in the brainstem and travels from the top of the midbrain to the medulla oblongata. These pathways have projecting reticular neurons that affect the cerebral cortex, cerebellum, thalamus, hypothalamus, and spinal cord. The reticular formation controls the body’s level of consciousness through the reticular activation system, also known as RAS. Sensory axons, found in visual, auditory, and sensory impulses, activate RAS neurons in the brain stem. These neurons then relay information to the thalamus and cerebrum. Continuous stimulation of the RAS neurons causes the cerebrum to stay in an aroused state; this gives the feeling of alertness. However, RAS can filter out repetitive, weak stimuli; this prevents the brain from responding to unimportant information, as well as being sensory overloaded.
Spinal cord: The spinal cord proper extends from the foramen magnum of the skull to the first or second lumbar vertebrae. It creates a two-way pathway between the brain and the body and divides into four regions – cervical, thoracic, lumbar, and sacral. These regions are then broken down into 31 segments with 31 pairs of spinal nerves. There are 8 cervical nerves, 12 thoracic nerves, 5 lumbar nerves, 5 sacral nerves, and 1 coccygeal nerve. Each nerve exits the vertebral column passing through the intervertebral foramina and to its designated location in the body.
Due to cervical and lumbar enlargements, the spinal cord differs in width throughout its structure. The cervical enlargement occurs at C3 to T1, and the lumbar enlargement is at L1 to S2. The white matter is present on the outside of the spinal cord, with gray matter located in its core and cerebrospinal fluid in the central canal. The gray commissure, the dorsal, lateral, and ventral horns are all composed of gray matter. The gray commissure surrounds the central canal. The dorsal horns are made of interneurons, while the ventral horns are somatic motor neurons. Afferent neurons in the dorsal roots carry impulses from the body’s sensory receptors to the spinal cord, where the information begins to be processed. The ventral horns contain efferent motor neurons, which control the body’s periphery. The axons of motor neurons are found in the body’s skeletal and smooth muscle to regulate both involuntary and voluntary reflexes.
The spinal cord ends in a cone-shaped structure called conus medullaris and is supported to the end of the coccyx by the filum terminale. Ligaments are found throughout the spinal column, securing the spinal cord from top to bottom.
Ascending pathway to the brain: Sensory information travels from the body to the spinal cord before reaching the brain. This information ascends upwards using first, second, and third-order neurons. First-order neurons receive impulses from skin and proprioceptors and send them to the spinal cord. They then synapse with second-order neurons. Second-order neurons live in the dorsal horn and send impulses to the thalamus and cerebellum. Lastly, third-order neurons pick up these impulses in the thalamus and relay it to the somatosensory portion of the cerebrum. Somatosensory sensations are pressure, pain, temperature, and the body’s senses.
Descending pathway: Descending tracts send motor signals from the brain to lower motor neurons. These efferents neurons then produce muscle movement.[6]
Embryology
The adult brain and spinal cord begin to form during week 3 of embryological development. The ectoderm begins to thicken, forming the neural plate. The neutral place then folds inwards, creating the neural groove. Neural folds that migrate laterally flank the neural groove. The neural groove then develops into the neural tube, which forms the CNS structures.
The neural tube gets separated into an anterior and posterior end. The anterior end forms the primary brain vesicles, prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain), while the posterior end becomes the spinal cord. The primary brain vesicles continue to differentiate, creating secondary brain vesicles. The forebrain separates to form the telencephalon and diencephalon, and the hindbrain splits to form the metencephalon and the myelencephalon (spinal brain).[7] The midbrain does not divide and stays the mesencephalon. The development of the secondary brain vesicles produces the adult brain structures
Telencephalon to cerebrum
Diencephalon to hypothalamus, thalamus, retina
Mesencephalon to the brain stem (midbrain)
Metencephalon to the brain stem (pons), cerebellum
Myelencephalon to the brain stem (medulla oblongata)
The central part of the neural tube forms continuous, hollow cavities known as ventricles. During month 6 of gestation, the cerebral cortex changes from a smooth to wrinkled, convoluted appearance; this is due to the continued growth of the cerebral hemispheres. The elevated parts of the ridges are gyri, while the grooves have the name sulci. The convolutions allow for the increased surface area of the brain to fit within the skull. Throughout the brain, there are areas of white and gray matter. The gray matter contains neuronal cell bodies, dendrites, glia, and unmyelinated neurons. Contrary, white matter is composed of myelinated axons.[7]
The spinal cord, formed from the caudal portion of the neural tube, is composed of both gray and white matter. At 6 weeks of gestation, the gray matter begins to aggregate, forming the dorsal alar plate and ventral basal plate. Interneurons form from the alar plate, while motor neurons form from the basal plate. Dorsal root ganglia, which brings information from the periphery to the spinal cord, arise for the neural crest cells.
Blood Supply and Lymphatics
Due to the importance and delicate nature of the central nervous system, the body closely monitors the blood traveling to and from it. The cardiovascular system ensures continuous, oxygenated blood as a drop-in oxygenation level can be detrimental. The common carotid arteries branch off of the aorta, which carries oxygen-rich blood from the heart for distribution. The common carotid further branches into right and left internal and external carotid arteries, which supply the cranium with blood. Vertebral arteries begin in the neck and branch as they enter into the skull through the foramen magnum. They supply the anterior portion of the spinal cord. The vertebral arteries then merge into the basilar artery. The basilar artery is responsible for delivering blood to the brainstem and cerebellum. The circle of Willis ensures that blood will continue to circulate even if one of the arteries is not working appropriately. The internal carotid and vertebral arteries compose the circle of Willis.[8] After being used in the CNS, blood then travels back to the lungs for oxygenation. Multiple dural venous sinuses do this:
Superior sagittal sinus
The confluence of sinuses
Transverse sinuses
Sigmoid sinuses
Jugular veins
Carotid arteries
Superior vena cava
Lungs
Surgical Considerations
Anesthesia is a controlled state of temporary loss of sensation that allows the performance of painful medical procedures that would otherwise be unfeasible. There are many types of anesthesia, such as general, sedation, and local. However, they are all used to disrupt the cellular and intracellular communication in the central and peripheral nervous system.
General anesthesia involves the use of an analgesic, paralytic, and amnesia, which all work together to render the patient unconscious. Under general anesthesia, the activity of the central nervous system undergoes complete suppression, and there is a total loss of sensation. Neuromuscular blockers are used, requiring intubation and subsequent mechanical ventilation. Depolarizing neuromuscular blockers, such as succinylcholine, binds to the postsynaptic cholinergic receptors causing depolarization. However, the removal of succinylcholine from the receptors is much slower, which inhibits the binding of acetylcholine and therefore, prevents future depolarizations. Non-depolarizing neuromuscular blockers, like vecuronium, act as an acetylcholine inhibitor blocking the postsynaptic cholinergic receptors. However, when these neuromuscular blockers bind, they do not change the permeability of the ion channels.[9]
During regional anesthesia, the anesthesiologist numbs only the portion of the body that is the target of the operation. Spinal and epidurals are used as a local anesthetic medication and get injected into the vertebral canal. Spinal anesthesia targets the spinal fluid, while the epidural injection is into the epidural space.
As with any surgical procedures, there is always a risk when going under anesthesia. Conditions that increase the risk of having a complication are obesity, diabetes, hypertension, and any disease process of the respiratory and cardiovascular system.[10]
Neurosurgeons have received training in the diagnosis and treatment of patients with injuries or diseases affecting the central nervous system. They provide operative management of neurological disorders, such as tumors, stroke, head, and spinal injuries, chronic pain, etc. Any surgical procedures have risks, especially when dealing with delicate nervous tissue in the brain and spinal cord. Complications of brain surgery, including bleeding in the brain, speech, memory, coordination issues, stroke, brain swelling, and possible coma.
Clinical Significance
Wernicke aphasia: Wernicke aphasia occurs most commonly as a result of a hemorrhagic or ischemic stroke. Strokes that occur in the left middle cerebral artery prevent oxygenated blood from reaching the Wernicke area. In Wernicke aphasia, a person can speak clearly and produce speech. However, their speech has no meaning. They have difficulty understanding language.
Broca aphasia: Broca aphasia, also known as expressive aphasia, is caused by a stroke, brain tumor, or brain trauma. When a stroke occurs in the Broca area, oxygen is cut off to that part of the brain. The hypoxia causes irreversible damage. During Broca aphasia, the person has difficulty producing speech. They can comprehend and know what they want to say; however, they are unable to form the words to communicate the message.[11]
Traumatic brain injuries: Traumatic brain injuries (TBI) occur when there is a disruption to normal brain activity, which can occur during a sports injury, a car accident, by a penetrating object, or even a blunt object. TBI symptoms can vary depending on the severity of the injury. For example, a concussion can cause temporary dizziness or loss of consciousness, while a contusion causes lasting neurological damage. Contusions to the brain stem resulting in a coma. TBI can cause subdural or subarachnoid hemorrhage and cerebral edema. When the brain sustains a trauma, the blood vessels in the brain break. The blood begins to pool, increasing the intracranial pressure, and compressing the brain tissue. As the brain pushes through the skull onto the spinal cord, autonomic nervous system functions are lost.
Cerebrovascular Accidents: Cerebrovascular accidents, also known as strokes, occur when the brain is not able to get oxygenated blood. The lack of oxygen causes hypoxia, and tissues in the brain start to die. Commonly, strokes are caused by a blood clot that has traveled from one location in the body to the cerebral artery in the brain. Dependent on where the clot lands, determine the symptoms of the stroke. For example, some people may experience left-sided paralysis, while others might have slurred speech. Transient ischemic attacks are considered small strokes as their symptoms are more temporary. In any CVA, time is crucial. If necessary, doctors can administer tissue plasminogen activator which breaks down the clot or can surgically remove it. The severity of symptoms directly correlates to how long the brain’s oxygen supply has been cut off.
Alzheimer’s disease: Alzheimer’s disease (AD) is a common type of dementia in which one’s brain cells and neural connections begin to degenerate and die. This condition presents with loss of memory and cognitive decline. Alzheimer’s is progressive, with symptoms worsening over time.[12] Scientists have found aggregations of beta-amyloid plaques and neurofibrillary tangles made of tau within the neurons in AD patients. These plaques and tangles result in the death of brain cells and form because of the misfolding of proteins within them. AD patients have a decrease in neural activity in the parietal cortex, hippocampus, and basal forebrain.
Parkinson’s disease: Parkinson’s disease is a nervous system disorder that results in the deterioration of dopamine-releasing neurons in the substantia nigra.[13] The drop-in dopamine levels create tremors, unsteady movements, and loss of balance. Parkinson’s disease is progressive as it usually starts as a tremor in one hand. Many patients exhibit a pill-rolling movement in their hand, bradykinesia, stiffness, and a mask life face as symptoms progress. A Parkinson’s disease diagnosis results from looking at the patient’s symptoms, medical history, and a neurological and physical exam. While no cure exists for the disease, the severity of the symptoms can be controlled. Levodopa can pass through the blood-brain and undergo conversion into dopamine for CNS use. Deep brain stimulation is a surgical option that can stop the abnormal brain activity and thus control the tremors. However, deep brain stimulation does not keep the disease from progressing.
Huntington disease: Huntington disease is a hereditary, progressive brain disorder that is caused by a mutation in the huntingtin gene, HTT. The CAG segment in the HTT gene normally repeats up to 35 times. However, in someone with Huntington’s disease, the CAG segment is repeated up to 120 times. This large CAG segment causes the huntingtin protein to accumulate in the brain cells, which eventually leads to cell death. Initially, Huntington disease causes chorea, involuntary jerking, and hand-flapping movements. As the disease progresses, cognitive decline occurs. Fatally follows within 15 years of diagnosis.
Spinal cord traumas: Symptoms of spinal cord injuries is dependent on where the injury occurs. If damage to the sensory tracts occurs, the sensation can be affected. However, if the ventral roots or ventral horns are damaged, paralysis occurs. Flaccid paralysis is when nerve impulses do not reach the intended muscles. Without stimulation, the muscles are unable to contract. Spastic paralysis is when the motor neurons undergo irregular stimulation, causing involuntary contraction. Paraplegia, paralysis of the lower limbs, occurs when the spinal cord gets cut between T1 and L1. Quadriplegia, paralysis of all limbs, is a result of an injury in the cervical region.
Poliomyelitis: Poliomyelitis is an inflammation of the spinal cord due to the virus, Polio. Poliovirus spreads from human to human or through infected food and water. It demolishes the neurons in the ventral horn of the spinal cord leading to paralysis. The infection of the poliovirus is preventable through the administration of the vaccine.[14]
Amyotrophic Lateral Sclerosis: Amyotrophic lateral sclerosis, known also as ALS and Lou Gehrig disease, destroys motor neurons that control voluntary and involuntary movements like breathing, speaking, and swallowing. The cause of ALS is not known, and unfortunately, there is no cure. Scientists believe that cell death is related to the excess amount of extracellular glutamate in ALS patients. Riluzole, which can disrupt the formation of glutamate, is used to slow down the progression and reduce the painful symptoms of ALS.
Multiple sclerosis: Multiple sclerosis is an autoimmune disease, in which the body attacks the myelin proteins of the central nervous system, disrupting the communication between the brain and the body. MS has a high prevalence in young adults and presents as pain, weakness, vision loss, and loss in coordination. The severity of symptoms varies from patient to patient. Medication is used to suppress the body’s immune system and can help control the adverse effects of this disease.
Continuing Education / Review Questions
The Central Nervous System | Anatomy and Physiology
Learning Objectives
- Describe the 3 protective coverings of the brain: blood-brain barrier, meninges, cerebrospinal fluid
- Name the major regions of the brain
- Describe the connections between the cerebrum and brain stem through the diencephalon, and from those regions into the spinal cord
- Describe the functions of the major regions of the brain
- Describe the basic anatomy and physiology of the spinal cord
The CNS is crucial to the operation of the body, and any compromise in the brain and spinal cord can lead to severe difficulties. The function of the tissue in the CNS is crucial to the survival of the organism, so the contents of the blood cannot simply pass into the central nervous tissue. To protect the brain and spinal cord from external injuries due to physical trauma and internal damage caused by the toxins and pathogens that may be traveling through the blood stream, there are various protective structures surrounding the brain and spinal cord. The cranial bones and vertebrae are obvious structures that protect the nervous tissue of the brain and spinal cord from external trauma. There are other internal structures, however, that play a large role in protecting and maintaining homeostasis of nervous tissue. In this section, you will learn about the blood supply to the brain, the meninges, and cerebrospinal fluid.
Blood-brain Barrier
The CNS has a privileged blood supply, and there are multiple routes for blood to get into the CNS, with specializations to protect that blood supply. As discussed earlier, the neuroglial cells called astrocytes form a barrier between capillaries and neurons within the brain. Further, the capillaries within the brain are some of the most impermeable capillaries within the body, only allowing the most essential nutrients and minerals to enter the tissue. These capillaries along with the activity of the astrocytes form the blood-brain barrier.
Meninges
The outer surface of the CNS is covered by a series of membranes composed of connective tissue called the meninges, which protect the brain. The dura mater is a thick fibrous layer and a strong protective sheath over the entire brain and spinal cord. It is anchored to the inner surface of the cranium and vertebral cavity. The arachnoid mater is a membrane of thin fibrous tissue that forms a loose sac around the CNS. Beneath the arachnoid is a thin, filamentous mesh called the arachnoid trabeculae, which looks like a spider web, giving this layer its name. Cerebrospinal fluid circulates below the arachnoind mater in an area called the subarachnoid space. Directly adjacent to the surface of the CNS is the pia mater, a thin fibrous membrane that follows the convolutions of gyri and sulci in the cerebral cortex and fits into other grooves and indentations (Figure 8.18).
Figure 8.18. Meningeal Layers of Superior Sagittal Sinus The layers of the meninges in the longitudinal fissure of the superior sagittal sinus are shown, with the dura mater adjacent to the inner surface of the cranium, the pia mater adjacent to the surface of the brain, and the arachnoid and subarachnoid space between them. An arachnoid villus is shown emerging into the dural sinus to allow CSF to filter back into the blood for drainage.
Disorders of the Meninges
Meningitis is an inflammation of the meninges, the three layers of fibrous membrane that surround the CNS. Meningitis can be caused by infection by bacteria or viruses. The particular pathogens are not special to meningitis; it is just an inflammation of that specific set of tissues from what might be a broader infection. Bacterial meningitis can be caused by Streptococcus, Staphylococcus, or the tuberculosis pathogen, among many others. Viral meningitis is usually the result of common enteroviruses (such as those that cause intestinal disorders), but may be the result of the herpes virus or West Nile virus. Bacterial meningitis tends to be more severe. The symptoms associated with meningitis can be fever, chills, nausea, vomiting, light sensitivity, soreness of the neck, or severe headache. More important are the neurological symptoms, such as changes in mental state (confusion, memory deficits, and other dementia-type symptoms). A serious risk of meningitis can be damage to peripheral structures because of the nerves that pass through the meninges. Hearing loss is a common result of meningitis. The primary test for meningitis is a lumbar puncture. A needle inserted into the lumbar region of the spinal column through the dura mater and arachnoid membrane into the subarachnoid space can be used to withdraw the fluid for chemical testing. Fatality occurs in 5 to 40 percent of children and 20 to 50 percent of adults with bacterial meningitis. Treatment of bacterial meningitis is through antibiotics, but viral meningitis cannot be treated with antibiotics because viruses do not respond to that type of drug. Fortunately, the viral forms are milder.
Interactive Link
Watch this video that describes the procedure known as the lumbar puncture, a medical procedure used to sample the CSF. Because of the anatomy of the CNS, it is a relative safe location to insert a needle. Why is the lumbar puncture performed in the lower lumbar area of the vertebral column?
Cerebrospinal Fluid
Cerebrospinal fluid (CSF) circulates throughout and around the CNS. The fluid is a clear solution with a limited amount of the constituents of blood. It is essentially water, small molecules, and electrolytes. Oxygen and carbon dioxide are dissolved into the CSF, as they are in blood, and can diffuse between the fluid and the nervous tissue. In the brain, CSF is produced by special capillaries called the choroid plexus and flows through the nervous tissue of the CNS. Specifically, CSF circulates to remove metabolic wastes from the interstitial fluids of nervous tissues and return them to the blood stream. The ventricles are the open spaces within the brain where CSF circulates. The CSF circulates through all of the ventricles to eventually emerge into the subarachnoid space where it will be reabsorbed into the blood. There are four ventricles within the brain. The first two are named the lateral ventricles and are deep within the cerebrum. The third ventricle is the space between the left and right sides of the diencephalon, which opens into the cerebral aqueduct that passes through the midbrain. The aqueduct opens into the fourth ventricle, which is the space between the cerebellum and the pons and upper medulla (Figure 8.19).
Figure 8.19. Cerebrospinal Fluid Circulation The choroid plexus in the four ventricles produce CSF, which is circulated through the ventricular system and then enters the subarachnoid space through the median and lateral apertures. The CSF is then reabsorbed into the blood at the arachnoid granulations, where the arachnoid membrane emerges into the dural sinuses.
Interactive Link
Watch this animation that shows the flow of CSF through the brain and spinal cord, and how it originates from the ventricles and then spreads into the space within the meninges, where the fluids then move into the venous sinuses to return to the cardiovascular circulation. What are the structures that produce CSF and where are they found? How are the structures indicated in this animation?
The Brain
The brain and the spinal cord are the central nervous system, and they represent the main organs of the nervous system. The spinal cord is a single structure, whereas the adult brain is described in terms of four major regions: the cerebrum, the diencephalon, the brain stem, and the cerebellum. A person’s conscious experiences are based on neural activity in the brain. The regulation of homeostasis is governed by a specialized region in the brain. The coordination of reflexes depends on the integration of sensory and motor pathways in the spinal cord.
The Cerebrum
The iconic gray mantle of the human brain, which appears to make up most of the mass of the brain, is the cerebrum (Figure 8.20). The wrinkled portion is the cerebral cortex, and the rest of the structure is beneath that outer covering. There is a large separation between the two sides of the cerebrum called the longitudinal fissure. It separates the cerebrum into two distinct halves, a right and left cerebral hemisphere. Deep within the cerebrum, the white matter of the corpus callosum provides the major pathway for communication between the two hemispheres of the cerebral cortex.
Figure 8.20. The Cerebrum The cerebrum is a large component of the CNS in humans, and the most obvious aspect of it is the folded surface called the cerebral cortex.Many of the higher neurological functions, such as memory, emotion, and consciousness, are the result of cerebral function. The cerebrum is covered by an outer area of gray matter called the cerebral cortex. This thin, extensive region of wrinkled gray matter is responsible for the higher functions of the nervous system. A gyrus (plural = gyri) is the ridge of one of those wrinkles, and a sulcus (plural = sulci) is the groove between two gyri. The pattern of these folds of tissue indicates specific regions of the cerebral cortex. The folding of the cortex maximizes the amount of gray matter in the cranial cavity. The surface of the brain can be mapped on the basis of the locations of large gyri and sulci. Using these landmarks, the cortex can be separated into four major regions, or lobes (Figure 8.19). The lateral sulcus that separates the temporal lobe from the other regions is one such landmark. Superior to the lateral sulcus are the parietal lobe and frontal lobe, which are separated from each other by the central sulcus. The posterior region of the cortex is the occipital lobe, which has no obvious anatomical border between it and the parietal or temporal lobes on the lateral surface of the brain. From the medial surface, an obvious landmark separating the parietal and occipital lobes is called the parieto-occipital sulcus. The fact that there is no obvious anatomical border between these lobes is consistent with the functions of these regions being interrelated.
Figure 8.21. Lobes of the Cerebral Cortex The cerebral cortex is divided into four lobes. Extensive folding increases the surface area available for cerebral functions.The lobes of the cortex exhibit functional differences. Areas within the occipital lobe are responsible for primary visual perception, 17 and 18 on the Brodmann’s figure below (Fig. 8.20). That visual information is complex, so it is processed in the temporal and parietal lobes as well. The temporal lobe is associated with primary auditory sensation, area 22 on Brodmann’s figure. Because regions of the temporal lobe are part of the limbic system, memory is an important function associated with that lobe also. Structures in the temporal lobe, such as the hippocampus, are responsible for establishing long-term memory, but the ultimate location of those memories is usually in the region in which the sensory perception was processed. The main sensation associated with the parietal lobe is somatosensation, meaning the general sensations associated with the body. Posterior to the central sulcus is the postcentral gyrus, the primary somatosensory cortex, which is identified as Brodmann’s areas 1, 2, and 3. All of the tactile senses are processed in this area, including touch, pressure, tickle, pain, itch, and vibration, as well as more general senses of the body such as proprioception and kinesthesia, which are the senses of body position and movement, respectively. Anterior to the central sulcus is the frontal lobe, which is primarily associated with motor functions. The precentral gyrus is the primary motor cortex. Cells from this region of the cerebral cortex are the upper motor neurons that instruct cells in the spinal cord to move skeletal muscles. Anterior to this region are a few areas that are associated with planned movements. The premotor area is responsible for thinking of a movement to be made. The frontal eye fields are important in eliciting eye movements and in attending to visual stimuli. Broca’s area is responsible for the production of language, or controlling movements responsible for speech; in the vast majority of people, it is located only on the left side. Anterior to these regions is the prefrontal lobe, which serves cognitive functions that can be the basis of personality, short-term memory, and consciousness. The prefrontal lobotomy is an outdated mode of treatment for personality disorders (psychiatric conditions) that profoundly affected the personality of the patient.
Figure 8.22. Brodmann’s Areas of the Cerebral Cortex Brodmann mapping of functionally distinct regions of the cortex was based on its cytoarchitecture at a microscopic level.Everyday Connections:
The Myth of Left Brain/Right Brain
There is a persistent myth that people are “right-brained” or “left-brained,” which is an oversimplification of an important concept about the cerebral hemispheres. There is some lateralization of function, in which the left side of the brain is devoted to language function and the right side is devoted to spatial and nonverbal reasoning. Whereas these functions are predominantly associated with those sides of the brain, there is no monopoly by either side on these functions. Many pervasive functions, such as language, are distributed globally around the cerebrum. Some of the support for this misconception has come from studies of split brains. A drastic way to deal with a rare and devastating neurological condition (intractable epilepsy) is to separate the two hemispheres of the brain. After sectioning the corpus callosum, a split-brained patient will have trouble producing verbal responses on the basis of sensory information processed on the right side of the cerebrum, leading to the idea that the left side is responsible for language function. However, there are well-documented cases of language functions lost from damage to the right side of the brain. The deficits seen in damage to the left side of the brain are classified as aphasia, a loss of speech function; damage on the right side can affect the use of language. Right-side damage can result in a loss of ability to understand figurative aspects of speech, such as jokes, irony, or metaphors. Nonverbal aspects of speech can be affected by damage to the right side, such as facial expression or body language, and right-side damage can lead to a “flat affect” in speech, or a loss of emotional expression in speech—sounding like a robot when talking.
The Diencephalon
The diencephalon is the one region of the adult brain that retains its name from embryologic development. The etymology of the word diencephalon translates to “through brain.” It is the connection between the cerebrum and the rest of the nervous system, with one exception. The rest of the brain, the spinal cord, and the PNS all send information to the cerebrum through the diencephalon. Output from the cerebrum passes through the diencephalon. The single exception is the system associated with olfaction, or the sense of smell, which connects directly with the cerebrum. The diencephalon is deep beneath the cerebrum and can be described as any region of the brain with “thalamus” in its name. The two major regions of the diencephalon are the thalamus itself and the hypothalamus (Figure 8.23).
Thalamus
The thalamus is a collection of nuclei that relay information between the cerebral cortex and the periphery, spinal cord, or brain stem. All sensory information, except for the sense of smell, passes through the thalamus before processing by the cortex. Axons from the peripheral sensory organs synapse in the thalamus, and thalamic neurons project directly to the cerebrum. It is a requisite synapse in any sensory pathway, except for olfaction. The thalamus does not just pass the information on, it also processes that information. For example, the portion of the thalamus that receives visual information will influence what visual stimuli are important, or what receives attention. The cerebrum also sends information down to the thalamus, which usually communicates motor commands.
Hypothalamus
Inferior and slightly anterior to the thalamus is the hypothalamus, the other major region of the diencephalon. The hypothalamus is a collection of nuclei that are largely involved in regulating homeostasis. The hypothalamus is the executive region in charge of the autonomic nervous system and the endocrine system through its regulation of the anterior pituitary gland. Other parts of the hypothalamus are involved in memory and emotion as part of the limbic system.
Figure 8.23. The Diencephalon The diencephalon is composed primarily of the thalamus and hypothalamus, which together define the walls of the third ventricle. The thalami are two elongated, ovoid structures on either side of the midline that make contact in the middle. The hypothalamus is inferior and anterior to the thalamus, culminating in a sharp angle to which the pituitary gland is attached.Brain Stem
The midbrain, pons, and the medulla oblongata are collectively referred to as the brain stem (Figure 8.24). The structure connects the brain to the spinal cord. Attached to the brain stem, but considered a separate region of the adult brain, is the cerebellum. The midbrain coordinates sensory representations of the visual, auditory, and somatosensory perceptual spaces. The pons is the main connection with the cerebellum. The pons and the medulla regulate several crucial functions, including the cardiovascular and respiratory systems and rates. The cranial nerves connect through the brain stem and provide the brain with the sensory input and motor output associated with the head and neck, including most of the special senses. The major ascending and descending pathways between the spinal cord and brain, specifically the cerebrum, pass through the brain stem.
Figure 8.24. The Brain Stem The brain stem comprises three regions: the midbrain, the pons, and the medulla.Midbrain
The midbrain is the most superior portion of the barinstem. It is located posterior to the hypothalamus and superior to the pons. It contains reflex centers for the head, eye, and body movements in response to visual and auditory stimuli. For example, reflexively turning the head to hear better or see better is activated by the midbrain.
Pons
The word pons comes from the Latin word for bridge. It is visible on the anterior surface of the brain stem as the thick bundle of white matter attached to the cerebellum. The pons is the main connection between the cerebellum and the brain stem. The bridge-like white matter is only the anterior surface of the pons; the gray matter beneath that is a continuation of the tegmentum from the midbrain. Gray matter in the tegmentum region of the pons contains neurons receiving descending input from the cerebrum and thalamus that is sent to the cerebellum. The pons works closely with the medulla to regulate respiratory activities.
Medulla
The medulla oblongata is the most inferior portion of the brain, and it’s connecting link with the spinal cord. It consists of ascending and descending tracts that are entering the brain for sensory integration and exiting the brain for motor responses. The medulla contains 3 integration centers that are vital for homeostasis: (1) the respiratory center that controls the rhythm of breathing and reflexes such as coughing and sneezing (2) the cardiac control center that regulates the rate and force of hear contractions (3) the vasomotor center that regulates blood pressure through vasoconstriction of blood vessels and vasodilation of blood vessels. Another area that spreads throughout the brain stem from the medulla up to the thalamus is the the reticular formation. The reticular formation is responsible for regulating general brain activity and attention. It is related to sleep and wakefulness.
The Cerebellum
The cerebellum, as the name suggests, is the “little brain.” It is covered in gyri and sulci like the cerebrum, and looks like a miniature version of that part of the brain (Figure 8.25). The cerebellum is largely responsible coordinating the interactions of skeletal muscles. It controls posture, balance, and muscle coordination during movement. Descending fibers from the cerebrum have branches that connect to neurons in the pons. Those neurons project into the cerebellum, providing a copy of motor commands sent to the spinal cord. Sensory information from the periphery, which enters through spinal or cranial nerves, is copied to a nucleus in the medulla known as the inferior olive. Fibers from this nucleus enter the cerebellum and are compared with the descending commands from the cerebrum. If the primary motor cortex of the frontal lobe sends a command down to the spinal cord to initiate walking, a copy of that instruction is sent to the cerebellum. Sensory feedback from the muscles and joints, proprioceptive information about the movements of walking, and sensations of balance are sent to the cerebellum through the inferior olive and the cerebellum compares them. If walking is not coordinated, perhaps because the ground is uneven or a strong wind is blowing, then the cerebellum sends out a corrective command to compensate for the difference between the original cortical command and the sensory feedback. Damage to the cerebellum may result in a loss of equilibrium, muscle contractions, and muscle tone.
Figure 8.25. The Cerebellum The cerebellum is situated on the posterior surface of the brain stem. Descending input from the cerebellum enters through the large white matter structure of the pons. Ascending input from the periphery and spinal cord enters through the fibers of the inferior olive. Output goes to the midbrain, which sends a descending signal to the spinal cord.The Spinal Cord
The description of the CNS is concentrated on the structures of the brain, but the spinal cord is another major organ of the system. The spinal cord is continuous with the brain. It descends from the medulla through the foramen magnum of the occipital bone and extends to the lumbar vertebrae. A cross-sectional view of the spinal cord reveals both gray matter and white matter (Fig. 8.26). The gray matter has the shape of a butterfly with outstretched wings and is centrally located to the white matter. The spinal cord has two basic functions. It transmits nerve impulses to and from the brain, and it serves as a reflex center for spinal reflexes.
Figure 8.26. Cross-section of Spinal Cord The cross-section of a thoracic spinal cord segment shows the posterior, anterior, and lateral horns of gray matter, as well as the posterior, anterior, and lateral columns of white matter. LM × 40. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)
Interactive Link
Watch this video to learn about the gray matter of the spinal cord that receives input from fibers of the dorsal (posterior) root and sends information out through the fibers of the ventral (anterior) root. As discussed in this video, these connections represent the interactions of the CNS with peripheral structures for both sensory and motor functions. The cervical and lumbar spinal cords have enlargements as a result of larger populations of neurons. What are these enlargements responsible for?
Disorders of the Basal Nuclei
Parkinson’s disease is a disorder of the basal nuclei, specifically of the substantia nigra, that demonstrates the effects of the direct and indirect pathways. Parkinson’s disease is the result of neurons in the substantia nigra pars compacta dying. These neurons release dopamine into the striatum. Without that modulatory influence, the basal nuclei are stuck in the indirect pathway, without the direct pathway being activated. The direct pathway is responsible for increasing cortical movement commands. The increased activity of the indirect pathway results in the hypokinetic disorder of Parkinson’s disease. Parkinson’s disease is neurodegenerative, meaning that neurons die that cannot be replaced, so there is no cure for the disorder. Treatments for Parkinson’s disease are aimed at increasing dopamine levels in the striatum. Currently, the most common way of doing that is by providing the amino acid L-DOPA, which is a precursor to the neurotransmitter dopamine and can cross the blood-brain barrier. With levels of the precursor elevated, the remaining cells of the substantia nigra pars compacta can make more neurotransmitter and have a greater effect. Unfortunately, the patient will become less responsive to L-DOPA treatment as time progresses, and it can cause increased dopamine levels elsewhere in the brain, which are associated with psychosis or schizophrenia.
Interactive Link
Visit this site for a thorough explanation of Parkinson’s disease.
The Central Nervous System in Your Body
The central nervous system (CNS) is comprised of the brain and spinal cord. The CNS receives sensory information from the nervous system and controls the body’s responses. The CNS is differentiated from the peripheral nervous system, which involves all of the nerves outside of the brain and spinal cord that carry messages to the CNS.
The central nervous system plays a primary role in receiving information from various areas of the body and then coordinating this activity to produce the body’s responses.
Central Nervous System Structure
The CNS has three main components: the brain, the spinal cord, and the neurons (or nerve cells).
The Brain
The brain controls many of the body’s functions including sensation, thought, movement, awareness, and memory. The surface of the brain is known as the cerebral cortex. The surface of the cortex appears bumpy thanks to the grooves and folds of the tissue. Each groove is known as a sulcus, while each bump is known as a gyrus.
The largest part of the brain is known as the cerebrum and is responsible for things such as memory, speech, voluntary behaviors, and thought.
The cerebrum is divided into two hemispheres, a right hemisphere, and a left hemisphere. The brain’s right hemisphere controls movements on the body’s left side, while the left hemisphere controls movements on the body’s right side.
While some functions do tend to be lateralized, researchers have found that there are not “left brained” or “right brained” thinkers, as the old myth implies. Both sides of the brain work together to produce various functions.
Each hemisphere of the brain is then divided into four interconnected lobes:
- Frontal lobes are associated with higher cognition, voluntary movements, and language.
- Occipital lobes are associated with visual processes.
- Parietal lobes are associated with processing sensory information.
- Temporal lobes are associated with hearing and interpreting sounds as well as the formation of memories.
Spinal Cord
The spinal cord connects to the brain via the brain stem and then runs down through the spinal canal, located inside the vertebra. The spinal cord carries information from various parts of the body to and from the brain. In the case of some reflex movements, responses are controlled by spinal pathways without involvement from the brain.
Neurons
Neurons are the building blocks of the central nervous system. Billions of these nerve cells can be found throughout the body and communicate with one another to produces physical responses and actions.
Neurons are the body’s information superhighway. An estimated 86 billion neurons can be found in the brain alone.
Protective Structures
Since the CNS is so important, it is protected by a number of structures. First, the entire CNS is enclosed in bone. The brain is protected by the skull, while the spinal cord is protected by the vertebra of the spinal column. The brain and spinal cord are both covered with a protective tissue known as meninges.
The entire CNS is also immersed in a substance known as cerebrospinal fluid, which forms a chemical environment to allow nerve fibers to transmit information effectively as well as offering yet another layer of protection from potential damage.
Human brain | Polyclinic “Medical Complex – Yelets”
The human nervous system is represented by the brain located in the cranial cavity; the spinal cord, located in the cavity of the spine, and the branched system of nerves that extend from the brain (cranial nerves) and innervate the organs of the head; a system of nerves that branch off from the spinal cord and innervate the arms, legs, trunk, and internal organs. The brain and spinal cord represent the central nervous system, and the nerve system represents the peripheral nervous system.
All formations of the nervous system consist of many neurons (cells of the nervous system) and their processes, along which nerve impulses are transmitted in ascending and descending directions due to the diverse connections that exist between neurons.
Despite the fact that different neurons perform different functions, and have differences in structure, they all have a body, a perceiving structure, and a process, a dendrite, a conducting structure.
According to their functional characteristics, neurons are divided into motor – executive, and sensitive – perceiving, as well as interneurons that interact between them.
The nerve cell performs two main functions: 1) processing of incoming information, transmission of nerve impulses and 2) biosynthetic, aimed at maintaining its life.
This is how the structure of a neuron looks schematically.
This is what the human brain looks like.
This is a very complex structure, consisting of many different entities that are in close interaction; carrying out conducting, analyzing, regulating and coordinating functions.All body movements, human feelings, the work of internal organs, his mind, intellect, memory, consciousness, sleep, wakefulness, everything is controlled by the brain. The human brain can be compared to a very complex computer with programs embedded in it, which are constantly being modified during a person’s life.
Schematically, the brain can be divided into lobes: frontal, occipital, temporal, parietal; cerebellum, brain stem. The lobes of the brain are covered with a cortex, which is a collection of highly differentiated neurons that carry out higher integrative activity.
In the frontal lobes there are centers for the regulation of voluntary movements, with the defeat of which weakness develops in the arms, legs on one side, or only the arms or legs. In the frontal lobes there are also centers of “arbitrary” rotation of the eyes and head, with the defeat of which there is a deviation of the eyes and head towards the pathological focus. In the frontal lobes there are also centers of coordination of movements, with the defeat of which there are disturbances in standing and walking.And, finally, with damage to the frontal lobe cortex, behavioral and mental disorders develop.
The parietal lobes are responsible for a person’s ability to recognize objects by touch, the ability to perform complex purposeful actions, the ability to decipher written signs and the ability to write.
The temporal lobes bear the auditory, gustatory and olfactory centers, the centers of understanding and reproduction of speech, the centers of coordination of movements.
In the visual lobes are the centers of perception of visual images, visual memory.The cerebellum is one of the main coordination centers.
In the brain stem are the centers of regulation of the life-supporting systems of organs, respiratory, cardiovascular, intermediate centers of regulation of cranial nerves, conducting pathways of the motor and sensory systems.
In the brain stem, in its lining, there are the nuclei of the cranial nerves, the bodies of the nerve cells responsible for the innervation of the organs of the head, the face, providing the function of the gustatory, auditory, visual, vestibular and olfactory analyzer.
There are cranial nerves of the caudal group: 1) Accessory nerve, pair 11, innervates the muscle that turns the head to the side. 2) Hyoid nerve, 12 pair, innervating tongue. 3) Glossopharyngeal nerve, 9 pair, innervating the pharyngeal muscles, tongue, palate, middle ear, salivary glands. 4) Vagus nerve, 10 pair, innervating the muscles of the pharynx, soft palate, larynx, smooth muscles of the bronchi, trachea, esophagus, stomach, intestines.
Further, the cranial nerves of the pontine-cerebellar angle are distinguished: 1) Facial nerve, 7 pair, innervating the muscles of the face.2) Vestibulo-cochlear nerve, 8 pair, innervating the inner ear. 3) Trigeminal nerve, 3 pairs, innervating the skin of the face, jaw, chewing muscles.
This is followed by a group of oculomotor nerves: 3, 4, 6 pairs.
And finally, the optic nerve, 2 pair, innervating the retina, and the olfactory nerve, 1 pair, innervating the nasal mucosa.
CENTRAL NERVOUS SYSTEM • Great Russian Encyclopedia
Book version
Volume 34.Moscow, 2017, pp. 287-288
Copy bibliographic reference:
Authors: N.P. Veselkin
CENTRAL NERVOUS SYSTEM (CNS), the central part of the nervous system of animals and humans; receives information from the environment, from all organs and systems of the body, processes and stores it, regulates and coordinates the responses of all systems of the body and its behavior.In vertebrates and humans, it consists of the brain and spinal cord; in invertebrates, it consists of a chain of ganglia. In the early stages of evolution, multicellular organisms developed a diffuse nervous system (for the first time in coelenterates). Subsequently, as a result of centralization, the central nervous system develops with the formation of nerve ganglia in invertebrates (annelids) and the predominant development of the head ganglia (cephalization). In molluscs and arthropods, as a result of the fusion of the cerebral ganglia, a single brain or cephalothoracic nerve mass (in spiders) arises.The nervous system of chordates developed in a different way: a segmented neural tube (spinal cord) is formed in them, as a result of cephalization, a brain is formed from its anterior end, which, as it evolves, undergoes a meaning. changes, although DOS. the principle of its division into departments remains.
Located in the vertebral canal, the spinal cord provides ascending and descending connections with the brain.It carries out a number of monosynaptic reflexes (without the participation of an intercalary neuron), when signals from a neuron of the spinal ganglion are switched directly to the motor. neuron and polysynaptic (including interneurons) reflexes (including tendon and flexion reflexes, stretch reflex). Under certain conditions, the spinal cord, without the participation of higher brain regions, is capable of reproducing a number of coordinated motor acts (walking, maintaining a posture).Located in the cranial cavity, the brain in higher mammals and humans is subdivided into the rhomboid (includes the medulla oblongata, pons varoli and cerebellum), middle (cerebral peduncles and quadruple), and anterior (diencephalon and terminal) brain. According to some researchers, the retina and the olfactory epithelium should also be attributed to the central nervous system, based on data on their embryonic development and structure.
Maincellular elements of the central nervous system – neurons with processes and glial cells. The former are linked by synapses that transmit information; there is also a synaptic between neurons and glial cells of a certain type. contacts. Neurons connected in series form neural chains, groups of neurons, united functionally, can make up neural networks. Neurons that receive information from the periphery, send fibers to the effector organ, and often intercalary neurons form a reflex arc.Groups of nerve fibers that connect certain parts of the central nervous system and are combined functionally and anatomically are designated as pathways. Through peripheral. the nervous system of the central nervous system is connected with all organs, receives and sends information along the spinal and cranial nerves.
The formation of the central nervous system – the main integrative system of the body – led to the development of fast-acting pathways both within the central nervous system and connecting the central nervous system with all organs and tissues of the body.This function is carried out by the peripheral nervous system, including the cranial and spinal nerves in vertebrates. Afferent (sensory) nerve fibers transmit excitation to the central nervous system from the peripheral. receptors, and efferent (motor) nerve fibers – from the central nervous system to the executive organs. Structural and functional features of the reflex arc determine the main. patterns of activity of the central nervous system. Diverse and numerous.body receptors perceive decomp. irritations, transform them into nervous excitement, which is transmitted to the executive organs, causing targeted reactions. The continuous flow of information from the executive organs is processed in the central nervous system, resulting in the correction and regulation of functions in accordance with the needs of the body. This process of reflex self-regulation is carried out according to the principle of feedback.For the center. departments of the reflex arc, capable of changing the rhythm of stimuli, are characterized by a relatively slow onset and flow of excitation and phase fluctuations in the level of excitability. Under the action of strong and prolonged stimuli, the nerve centers can come into a state of inhibition. The interaction of excitation and inhibition underlies all mechanisms of the central nervous system. The CNS carries out many different reflexes in a certain sequence according to the needs of the body.The coordination activity of the central nervous system is due to its structural (divergence and convergence of nerve pathways) and functional features. So, excitation processes can activate some synaptic. contacts and pathways in the central nervous system while blocking other synaptic inhibition. contacts and paths in a wide variety of combinations and space-time relationships. The activity of the central nervous system is based on a certain subordination (hierarchy) of its individual structures.In the process of evolution, the autonomy of some parts of the central nervous system decreases and the control role of others increases. Due to the close connection with the sensory organs, the center. department (cerebral ganglia, brain) becomes capable of integrating and coordinating the activity of the entire nervous system, and in mammals it is a material substrate of higher nervous activity. See also Nervous system.
Anatomy and Physiology of the nervous system
Development of the nervous system
The nervous system is divided into central and peripheral.The peripheral nervous system includes roots, plexuses, and nerves. The central nervous system consists of the brain and spinal cord. The study of the ontogeny of the central nervous system made it possible to establish that the brain is formed from cerebral vesicles resulting from the uneven growth of the anterior sections of the medullary tube. These bubbles form the forebrain, midbrain, and rhomboid brain. Later, from the forebrain, the telencephalon and diencephalon are formed, and the rhomboid brain is also divided into the hindbrain and medulla oblongata, respectively.
From the telencephalon, the cerebral hemispheres, basal ganglia, respectively, are formed from the diencephalon, the thalamus, epithalamus, hypothalamus, metathalamus, optic tracts and nerves, and the retina. The optic nerves and the retina are parts of the central nervous system, as it were, outside the brain. From the midbrain, the plate of the quadruple and the legs of the brain are formed. The pons and cerebellum are formed from the hindbrain. The brain bridge is bordered by the medulla oblongata below. The back of the medullary tube forms the spinal cord, and its cavity becomes the central canal of the spinal cord.In the endbrain, the lateral ventricles are located, in the diencephalon – the third ventricle, in the midbrain – the aqueduct of the brain, connecting the third and fourth ventricles; IV ventricle is located in the posterior and medulla oblongata.
Nerve cell morphology
Nerve cells form the basis of the nervous system. In addition to nerve cells, the nervous system contains glial cells and connective tissue elements.
The structure of nerve cells is different. There are numerous classifications of nerve cells based on the shape of their body, the length and shape of the dendrites, and other features.
According to their functional significance, nerve cells are subdivided into motor (motor), sensory (sensory) and interneurons.
The nerve cell performs two main functions: a) specific – the processing of information arriving at the neuron and the transmission of nerve impulses; b) biosynthetic, aimed at maintaining its life. This is also expressed in the ultrastructure of the nerve cell. The transfer of information from one nerve cell to another, the unification of nerve cells into systems and complexes of varying complexity determine the characteristic structures of a nerve cell – axons, dendrites and synapses.Organelles associated with the provision of energy metabolism, the protein-synthesizing function of the cell, etc., are found in most cells, in nerve cells they are subordinated to the performance of their main functions – the processing and transmission of information.
The body of a nerve cell in electron microscopic photographs is a rounded and oval formation. The nucleus is located in the center of the cell (or slightly eccentrically). It contains a nucleolus and is surrounded by external and internal nuclear membranes about 70 A each thick, separated by a variable perinuclear space.Lumps of chromatin are distributed in the karyoplasm, which tend to accumulate at the inner nuclear membrane. The amount and distribution of chromatin in the karyoplasm is variable in different nerve cells.
Elements of granular and non-granular cytoplasmic reticulum, polysomes, ribosomes, mitochondria, lysosomes, multibubble bodies and other organelles are located in the cytoplasm of nerve cells.
The structure of a nerve cell is represented by: mitochondria, which determine its energy metabolism; nucleus, nucleolus, granular and non-granular endoplasmic reticulum, lamellar complex, polysomes and ribosomes, which mainly provide the protein-synthesizing function of the cell; lysosomes and phagosomes are the main organelles of the “intracellular digestive tract”; axons, dendrites and synapses, providing morphofunctional communication of individual cells.The polymorphism of the structure of cells is determined by the different role of individual neurons in the systemic activity of the brain as a whole.
It is not possible to understand the structural and functional organization of the brain as a whole without analyzing the distribution of dendrites, axons and interneuronal connections.
Dendrites and their ramifications determine the receptive field of a particular cell. They are highly variable in shape, size, ramified and ultrastructure. Usually, several dendrites extend from the cell body.The number of dendrites, the form of their departure from the neuron, the distribution of their branches are decisive in the classifications of neurons based on silvering methods.
Electron microscopic examination reveals that the body of the nerve cells gradually turns into a dendrite, no sharp boundary and pronounced differences in the ultrastructure of the neuron soma and the initial section of a large dendrite are observed.
Axons, like dendrites, play an important role in the structural and functional organization of the brain and the mechanisms of its systemic activity.As a rule, one axon departs from the body of the nerve cell, which can then give off numerous branches.
Axons are covered with myelin sheath, forming myelin fibers. Bundles of fibers (which may contain individual unmyelinated fibers) make up the white matter of the brain, cranial and peripheral nerves.
When an axon passes into a presynaptic ending filled with synaptic vesicles, the axon usually forms a flask-like extension.
Interlacing of axons, dendrites and processes of glial cells creates complex, non-repeating patterns of the neuropil.However, it is the distribution of axons and dendrites, their mutual arrangement, afferent-efferent relationships, and the patterns of synapticarchitectonics that are decisive in the mechanisms of the closure and integrative functions of the brain.
Interconnections between nerve cells are carried out by interneuronal contacts, or synapses. Synapses are divided into axosomatic, formed by an axon with the body of a nerve cell, axodendritic, located between the axon and dendrite, and axo-axonal, located between two axons.Dendro-dendritic synapses located between dendrites are much less common.
In the synapse, a presynaptic process containing presynaptic vesicles and a postsynaptic part (dendrite, cell body or axon) are isolated. The active zone of the synaptic contact, in which the release of the mediator and the transmission of the impulse take place, is characterized by an increase in the electron density of the presynaptic and postsynaptic membranes, separated by the synaptic cleft. According to the mechanisms of impulse transmission, synapses are distinguished in which this transmission is carried out with the help of mediators, and synapses in which impulse transmission occurs electrically, without the participation of mediators.
An essential point in synaptic transmission is that different neurotransmitters are used in different systems of interneuronal connections. Currently, about 30 chemically active substances are known (acetylcholine, dopamine, norepinephrine, serotonin, GABA, etc.), which play a role in the synaptic transmission of impulses from one nerve cell to another.
Recently, numerous neuropeptides have been actively studied as intermediaries in synaptic transmission, among which enkephalins and endorphins, substance R.The release of a mediator or modulator of synaptic transmission from the presynaptic process is closely related to the structure of the postsynaptic receptive membrane.
Axonal transport plays an important role in interneuronal connections. Its principle is that a number of enzymes and complex molecules are synthesized in the body of a nerve cell, which are then transported along the axon to its terminal sections – synapses.
The axonal transport system is the main mechanism that determines the renewal and supply of mediators and modulators in the presynaptic terminals, and also underlies the formation of new processes, axons and dendrites.
According to the concept of the plasticity of the brain as a whole, two interrelated processes take place in the brain: 1) the formation of new processes and synapses; 2) destruction and disappearance of some of the pre-existing interneuronal contacts.
Mechanisms of axonal transport, associated processes of synaptogenesis and growth of the finest branching of axons underlie learning. adaptation, compensation for impaired functions. Disorder of axonal transport leads to the destruction of synaptic endings and changes in the functioning of certain brain systems.
By acting with a number of medicinal substances and biologically active substances, it is possible to influence the metabolism of neurons, which determines their axonal transport, stimulating it and thereby increasing the possibility of compensatory and restorative processes.
Strengthening axonal transport, the growth of the thinnest branches of axons and synaptogenesis play a positive role in the normal functioning of the brain. In pathology, these phenomena underlie the reparative, compensatory-restorative processes.
In addition to the mechanisms of axonal transport of biologically active substances that go from the body of the nerve cell to the synapses, there is the so-called retrograde axonal transport of substances from the synaptic endings to the body of the nerve cell. These substances are necessary to maintain the normal metabolism of the bodies of nerve cells and, in addition, carry information about the state of their terminal apparatus.
Disruption of retrograde axonal transport leads to changes in the normal functioning of nerve cells, and in severe cases – to retrograde degeneration of neurons.
Spinal cord –
medulla spinalis
General characteristics
The spinal cord is located in the vertebral canal. It looks like a strand squeezed in the dorsoventral direction, covered with meninges.
Fig. 1. Dachshund’s spinal cord in the spinal canal.
Topographically, the spinal cord is subdivided into cervical (C1 – C8), thoracic (Th2 – Th23), lumbar (L1 – L7), sacral (S1 – S3), and caudal (Ca1 – Ca5). The anterior border of the spinal cord corresponds to the cranial edge of the arch of the atlas, and the posterior border: in dogs it reaches the cranial edge of the 7th lumbar vertebra, in cats – the third (last) sacral vertebra.Along the entire length of the spinal cord in dogs, there are two thickenings in the places where the nerves run to the extremities: cervical (from C6 to Th3), lumbar (from L4 to S2). In cats, in addition to the cervical thickening in the C6 region and the lumbar in the L5 region, there is also a thoracic thickening in the Th22 region. After lumbar thickening, the spinal cord sharply narrows, forming a spinal cone, which passes into the filum terminale. The initial section of the filum terminale contains the nerve tissue of the spinal cord, represented by the ependymal tube or its extension – the terminal ventricle (continuation of the central spinal canal), reaching L7 / S1 in the dog and Ca1 in the cat.The terminal section of the terminal filament, terminating in the dog at the Ca1-Ca3 level, and in the cat at the Ca4-Ca6 level, is represented by the dura mater of the spinal cord. The spinal cone, terminal filament, and caudal nerves form a cauda equina.
- a – conus medullaris
- b – end thread
- s- subarachnoid space of the spinal cord
- d- dura mater
- e- thin end thread of a hard sheath
- f- cavum epidurale epidural cavity.
Due to the advancing growth of the spinal column, the boundaries of the spinal cord segments do not coincide with the boundaries of the vertebrae of the corresponding sections. In a dog, the 3rd sacral neurosegment and the spinal cone, which includes the tail neurosegments, lie in the region of the 6-7 lumbar vertebra, and in cats – in the region of the sacral bone. The spinal cord of a cat is about 40cm long and weighs 8-9g, a small dog (dachshund) – 48cm and weighs 14g, a large dog (German shepherd) – 78cm and weighs 33g. Spinal cord membranes.(Fig. 2) The dura mater ( dura mater spinalis, s. Pachymeninx ) is external, built of dense connective tissue. Covers the spinal cord and spinal nerves up to their exit from the intervertebral foramen. Attaching to the arches of the Atlantean, the epistropheus tooth, along the edges of the intervertebral foramen and tail vertebrae, the hard spinal membrane keeps the spinal cord in suspension on a kind of stretch marks. Between the hard shell and the periosteum of the spinal canal there is an epidural space filled with adipose tissue and venous plexus.It protects the spinal cord from mechanical shocks and ensures its mobility in the spinal canal. The presence of the epidural space makes it possible to carry out anesthesia of the spinal nerve roots on their way to the intervertebral foramen. Epidural anesthesia is performed in a dog and a cat between the 7 lumbar and 1 sacral vertebrae, between the sacrum and 1 caudal vertebra, or between the next 2-3 caudal vertebrae, depending on the goal pursued.
Arachnoid membrane ( arachnoidea spinalis ) – middle, built of loose connective tissue, separated from the dura mater by an insignificant subdural space filled with tissue fluid (some authors claim that dogs and cats do not have this space).
The pia mater (choroid) ( pia mater spinalis ) – internal, consists of dense connective tissue. Blood vessels pass through it, which, entering the brain tissue, provide a strong connection between the soft membrane and the spinal cord. From the soft membrane in each segment of the spinal cord, the odontoid ligaments extend, which, piercing the arachnoid membrane, attach to the hard spinal cord, suspending the spinal cord inside it. The soft membrane is separated from the arachnoid membrane by the subarachnoid (subarachnoid) space filled with cerebrospinal fluid.
Fig. 2. The membranes of the brain.
The structure of the spinal cord
The ventral median fissure (the location of the central spinal artery and vein) and two lateral ventral grooves (the exit point of the ventral roots of the spinal nerves) run along the ventral surface of the spinal cord. The dorsal median groove and dorsal lateral grooves (the place of entry of the dorsal roots of the spinal nerves) run along the dorsal surface.
The spinal cord consists of a white medulla located along the periphery and a gray medulla lying in the center. The gray medulla in cross section resembles the outline of the letter H or the wings of a butterfly. The central canal of the spinal cord passes through the bridge connecting both legs of the H-shaped gray matter, the gray commissure (central intermediate). At the border of the spinal cord and medulla oblongata, the central canal expands and passes into the 4th cerebral ventricle.In the area of the lumbar thickening of the spinal cord, the central canal also expands, forming the terminal ventricle,
which, in turn, narrowing, blindly ends in a terminal thread. The shape of the central canal is in the form of an elongated oval, about 100 µm in height in cats and dogs and about 50 µm in width.
In each half of the spinal cord, the gray matter occurs in the form of dorsal and ventral columns, separated by a lateral and central intermediate substance. In the lower part of the dorsal pillars, a reticular formation is located laterally, which is represented by a transverse network of nerve fibers.It is most pronounced in the cervical region, and least pronounced in the thoracic and lumbar regions.
Centers that control unconditioned reflexes are located in the gray matter of the spinal cord. At the level of the thoracic segments there is a center that controls the muscles of the spinal column and chest, at the level of the lumbar segments are the centers of the musculature of the pelvic limbs, at the level of the last lumbar segments are the centers of defecation and urination. Morphologically, the centers are represented by the nuclei of the gray medulla.The nucleus is formed by the bodies of nerve cells according to the principle of a single origin, structure and function. The dorsal column contains its own dorsal nucleus (relay in the conduction of impulses of pain sensitivity) and the thoracic nucleus (participates in the control of proprioceptive sensitivity from skeletal muscles to the cerebellum). In the middle part there are vegetative nuclei: sympathetic – in the thoracolumbar region from C8 / Th2 to L4 / L5 (intermediate medial nucleus) and parasympathetic – in the sacral region from S1 to S3 (intermediate lateral nucleus).In the ventral column is the motor nucleus, from the cells of which somatomotor fibers extend. In addition to these nuclei, there are switch neurons, adhesion cells and associative cells (provide communication between the nuclei), cord cells (form their axons with paths connecting the spinal cord and brain). The white medulla consists of nerve fibers and forms the pathways. It is more in the cranial part of the spinal cord, and in the caudal direction the amount of white matter gradually decreases.Columns of the gray medulla divide the white matter of the spinal cord into paired dorsal, lateral and ventral cords. The white medulla located between the dorsal columns is completely divided into 2 halves by the median dorsal septum. Both ventral cords are connected by a white commissure located ventrally from the gray commissure. The corresponding structure is absent on the dorsal side. Ascending fibers pass in the dorsal cord, which conduct sensory impulses (tactile and compression sensitivity) without switching in the spinal cord from the periphery to the medulla oblongata.Fibers from the posterior part of the body, especially from the hind limb, form a thin bundle ( fasciculus cracilis ), which adjoins the dorsal median septum in the midline. Fibers from the front of the body, especially from the forelimbs, attach laterally to the thin bundle, while forming a wedge-shaped bundle ( fasciculus cuneatus ). Both bundles on the dorsal surface of the spinal cord are noticeable as cords, and upon transition to the medulla oblongata are combined into the medulla oblongata ( tractus spinobulbaris ).Ascending and descending paths pass in the lateral cord. The ascending pathways are located in the outer part of the cord and are represented by the dorsal spinal cord fasciculus ( fasciculus spinocerebralis dorsalis ), the ventral spinal cord fasciculus ( fasciculus spinocerebralis ventralis ), the ascending fasciculus spinocerebralis ventralis ), the ascending fasciculus spinocerebralis ventralis in cats, it is dorsolateral and is a conductor of pain sensitivity. The descending pathways consist of a lateral bundle emerging from the red nucleus ( fasciculus rubrospinalis ), a vestibulospinal bundle ( fasciculus vestibulospinalis ), which lies ventral to the previous and lateral pyramidal bundle ( tractus corticospinalis later-alis s.piramidalis ), which is better expressed in dogs and cats than in other domestic animals. It is formed by the descending fibers of the sigmoid, coronary and ectosylvian gyri of the cerebral cortex and ends on the intermediate neurons of the spinal cord. Only a small fraction of the fibers in dogs and cats terminate in motor spinal neurons. The intersection of the pyramidal path near the medulla oblongata in dogs and cats has little effect on motor functions. The greatest changes occur when the motor centers in the cerebral cortex are damaged.The ventral cord is a descending path and includes a ventral or straight pyramidal bundle ( fasciculus corticospinalis ventralis ) and a quadruple bundle ( fasciculus tectospinalis ). The ascending and descending pathways do not directly adjoin the gray matter. A narrow strip of white matter in the form of its own bundles connects the ascending and descending segments on one side (associative cells) or the right and left sides of the spinal cord (commissural cells).
Spinal cord vessels
Arteries of the spinal cord are the spinal branches of the vertebral, intercostal, lumbar and sacral arteries.All these branches penetrate into the spinal canal along the roots of the spinal nerves and form three longitudinal highways on the spinal cord:
1. Unpaired ventral spinal artery – lies together with the artery of the same name in the ventral median fissure, gives off branches to the gray medulla,
2. Paired dorsal spinal arteries – lie along the dorsal nerve roots, and the corresponding veins – along the ventral roots. All three arterial lines anastomose each other in each segment, forming a vascular crown.Branches branch off from it into the white medulla, connecting inside the brain with the arteries of the gray matter. From the veins, blood flows into the venous plexus and the paired vertebral ventral sinus. It lies in the epidural space and connects to the segmental veins of the trunk.
1. Aorta
2. Intercostal arteries
3. Dorsal branch
4. Musculocutaneous branch
5. Spinal branch
6. Ventral radiculomedular artery (the place of transition to the ventral spinal artery)
7.Dorsal radiculo – medullary artery 8 dorsal spinal artery.
Sulcocomisural artery
Dogs do not have Adamkevich’s artery, this artery is present only in humans and primates, this is a significant difference in the blood supply to the spinal cord
– Peripheral nerves
– Brain
1. Medulla oblongata
2. Brain bridge
3. Midbrain
4. Cerebellum
5. Diencephalon
6. Cerebral cortex
– Liquor circulation
– Blood supply to the central nervous system.
Interactive functions of the spinal cord (MEDULLA SPINALIS)
Spinal cord – the most caudal part of the central nervous system
A feature of the spinal cord is a clearly defined segmental structure
The total number of segments corresponds to the number of body metameres (a metamere is a segment that receives sensory fibers from one separate pair of dorsal roots). The skin area that is innervated by these sensory nerves is called the dermatome.
One pair of anterior or ventral roots and one pair of posterior or dorsal roots extend from each segment. The functional significance of these roots is different. Bell and Magendie found that the ventral roots are composed of efferent, “motor” fibers, the dorsal – of afferent, “sensitive” fibers. The established pattern is defined as “Bella-Magendie law”. The anterior and posterior roots outward from the spinal nodes in the intervertebral foramen are connected to the mixed spinal nerve, which, when leaving the spine, is divided into dorsal, ventral branches and a branch heading to the sympathetic trunk (rammus communicans).
The spinal cord is divided into sections:
– cervical,
– thoracic,
– lumbar,
– sacral caudal.
There are two fusiform thickenings along the spinal cord. The cervical thickening is formed by four cervical segments and the first thoracic segments, the lumbar thickening is formed by four lumbar segments and three sacral segments. These thickenings correspond to the exit sites of the nerve roots for the fore and hind limbs from the spinal cord.The spinal cord is composed of white matter, made up of myelinated nerve fibers, and gray matter, containing nerve cells. The gray matter of the spinal cord lies inside and is surrounded by white matter on all sides. The column of gray matter forms three protrusions: ventral, dorsal and lateral, which are horn-shaped on transverse sections of the brain. Accordingly, a distinction is made between ventral, dorsal and lateral. The cross-sectional view of the gray matter, according to many researchers, resembles the letter “H” or a butterfly with open wings.the ventral horn has a rounded shape and contains cells that give rise to the anterior motor roots. The dorsal horn is narrower and longer than the anterior horn, contains cells that give rise to the posterior sensory roots. The lateral horn is determined throughout the last cervical, all thoracic and I-II lumbar segments of the spinal cord. The lateral horn forms a small triangular projection of the lateral edge of the gray matter. It contains small neurons, the axons of which exit from the spinal cord together with the ventral and partly dorsal nerve roots.The neural composition of the gray matter of the spinal cord is complex.
The following types of neurons are distinguished:
- Efferent neurons, which are subdivided into alpha motor neurons and gamma motor neurons.
- Preganglionic neurons. Their axons form preganglionic nerve fibers that travel to the ganglia of the border nerve column.
- Interneurons are the largest group of neurons involved in the integration of excitation and inhibition processes.The processes of these neurons mainly provide intrasegmental and intersegmental connections.
- Afferent neurons. Neurons of this type have one axon, which divides in a T-shape. One branch of such a neuron transmits excitation from the receptor to the body of the nerve cell, the other branch provides the conduction of excitation from the body of the spinal neuron to other spinal neurons. Efferent neurons are located in the anterior horn and are the motor centers of the spinal cord. Afferent neurons are located in the dorsal horn and are the centers that receive afferentation from receptors.The nerve cells of the lateral horn are the autonomic centers of the spinal cord.
In 1925, the American anatomist B. Rexed proposed to divide the gray matter of the spinal cord into ten plates or layers, the surfaces of which are located parallel to the dorsal or ventral surface of the spinal cord. Plates are designated by Roman numerals. Essentially, Rexed proposed a ten-plate functional topography of the spinal cord neurons. They are as follows: I-IV plates form the head of the dorsal horn of the gray matter – this is the primary sensory area.Most of the afferent fibers from the trunk and limbs are projected into this area. From here originate several tracts of the spinal cord that go to the brain. V-VI plates form the neck of the dorsal horn. Here, the fibers from the sensorimotor area of the cerebral cortex and fibers that carry proprioceptive sensitivity from the trunk and limbs end. Plate VII represents the area of termination of propriospinal and visceral connections, as well as afferent and efferent connections of the spinal cord with the cerebellum and midbrain.That part of the VII plate, which is located in the region of the ventral horn, contains Renshaw cells. Plate VIII is characterized by bulbospinal and propriospinal connections. The X plate is the primary motor area and is composed of motor neurons. The motoneurons of this area are combined into functional groups, pools (English – a set). The X plate occupies the space around the spinal canal and is composed of neurons, glial cells, and commissural fibers.
Rexed Plates
– Plate I is the most superficial layer of the dorsal horn, it is also called the marginal layer.It contains large, flat “marginal cells” and intermediate-sized neurons.
– Plate II is called “gelatinous” because of its gelatinous appearance on a fresh cut of the spinal cord. It consists of small densely spaced cells.
– Plate III contains large loose cells.
– Plate IV, the thickest located in the posterior horn, is composed of large neurons with dendrites extending into other plates. Together, plates III and IV form their own nucleus (nucleus proprius).
– Plate V consists of small neurons.
– Plate VI is localized at the very base of the dorsal horn and can be traced only in the areas of thickening of the spinal cord (cervical and lumbar regions). The entire dorsal horn is formed by plates I-VI.
– Plate VII occupies an irregular area in the center of the gray matter of the spinal cord.
– Plate VIII covers the inner half of the anterior horn in the region of its cervical and lumbar thickenings.
– Plate IX corresponds to the location of a group of motor neurons in the ventral horn, and
– Plate X surrounds the central canal.Thus, the ventral horn is formed by plates VII-X.
The white matter of the spinal cord consists of nerve fibers, which are divided into endogenous, or own, fibers, and exogenous, or foreign. Endogenous fibers include those originating in the spinal cord; they can be long or short. The long ones are sent to the brain, the short ones form intersegmental connections.
The main long endogenous fibers, or bundles that run in an upward direction, are as follows:
- Gaulle beam.This path carries fibers from the lower limbs and lower torso.
- Burdakh’s bundle carries fibers from the forelimbs and the front half of the trunk. These bundles occupy the dorsal cords of the spinal cord and end in the region of the medulla oblongata.
- In the lateral columns of the spinal cord, the dorsolateral pathway passes through the pain and temperature afferentation.
- Straight cerebellar bundle, or Flexig bundle. This pathway begins in the cells of the posterior horn and ends in the structures of the cerebellum.
- Hovers’ crossed cerebellar bundle. It originates from the cells of the posterior horn of the opposite side, part of the fibers of the Govers bundle ends in the cerebellum ( tr.spino-cerebellaris ), in the nuclei of the medulla oblongata ( tr.spino-bulbaris ), in the tubercles of the quadruple ( tr.spino-tectalis ), visual tubercle ( tr.spino-talamicus lat. ).
- The dorsal-olivary fascicle passes at the border of the ventral and lateral columns. This bundle originates from the cells of the dorsal horn and ends in the region of the olives of the medulla oblongata.
Of the downstream beams, note:
- Pyramidal path ( tr. Cortico-spinalis ), which, after crossing the fibers in the medulla oblongata, is divided into two bundles. One of them goes in the lateral column of the opposite side of the spinal cord (crossing pyramidal path) and ends in the cells of the anterior horn of its side. Another pyramidal bundle goes in the anterior column of the same side of the spinal cord and ends in the cells of the anterior horn of the opposite side (straight pyramidal path).
- Monakov’s bundle ( tr. Rubro-spinalis ) originates in the red nuclei of the midbrain, after leaving which it crosses (Trout’s cross) and ends in the cells of the ventral horn.
- The reticulo-spinal pathway ( tr. Reticulo-spinalis ) originates from the reticular formation of the opposite or its side and ends in the cells of the ventral horn.
- Vestibulospinal bundle (vestibular-spinal path, tr.vestibulo-spinalis ) originates from the cells of the Deiters nucleus and ends in the cells of the ventral horn.
- Helveg’s bundle ( tr. Praeolivaris ) originates from the tegmental area and ends in the cells of the ventral horn of the cervical spinal cord.
- Posterior longitudinal fascicle ( fasc.longitudinalis dorsalis ) starts from various cells of the brain stem and ends in the cells of the ventral horn
- Pre-dusky bundle ( tr.tecto-spinalis ) originates in the tubercles of the quadruple, forms a cross and ends in the cells of the ventral horn.
- Fasc. praepyramidalis Thomas begins in the reticular formation of the trunk and ends in the cells of the ventral horn of the cervical spinal cord.
The system of the ascending pathways carries out the function of conducting impulses from receptors that receive information from the external world and the internal environment of the body. Depending on the type of sensitivity that they conduct, the ascending conductors are divided into paths of extero-, proprio- and interoceptive sensitivity.The system of descending pathways carries out the function of conducting impulses from various parts of the brain to the motor nuclei (cells) of the spinal cord. In functional terms, the descending conductors can be characterized mainly as a system of fibers that carry out a motor function. It should be noted that in recent years, the possibility of conducting afferentation to such centers of the medulla oblongata as respiratory, vasomotor and digestive [Merkulova N.A., Inyushkin A.N., Belyakov V.I., Zainulin R.A. etc.
Reflex functions of the spinal cord
The study and analysis of the reflex functions of the spinal cord should be carried out on a “spinal animal”. A “spinal animal” is an animal in which, among all the parts of the central nervous system, only the spinal cord is preserved. To “prepare” a “spinal animal” it is necessary to cut the brain caudal to the medulla oblongata. In all vertebrates, transection of the brain under the medulla oblongata completely or significantly suppresses the reflex activity of the spinal cord.The state of suppression of the reflex activity of the brain is known as shock (meaning shock, concussion).
This name was given by the English scientist Marshal Hall (1835). The phenomenon of shock is found in various vertebrates to varying degrees. The higher the evolutionary stage that an animal occupies, the longer the state of shock. In humans and higher apes, after cutting the spinal cord, the state of shock continues for several years, and sometimes the ability to reflex activity is lost forever [Beritov, 1948].In cats and dogs, reflex activity is restored after a few days or weeks; in rabbits – after a few hours; for amphibians, in one to ten minutes. In lower mammals, in all lower vertebrates, a state of shock is observed mainly in relation to skeletal muscles. Of the vegetative organs, only the organs of the vascular system are exposed to shock.
But in higher vertebrates, shock equally affects both the somatic and the vegetative systems: paralysis of motor reflex reactions, respiratory arrest, a sharp drop in blood pressure, “paralysis” of the intestines, bladder, and a decrease in body temperature are observed.The state of shock during brain transection is not manifested to the same extent in all elements of the spinal cord. Analysis of the bioelectrical activity of spinal cord neurons revealed that the state of shock after spinal cord transection is mainly affected by motor neurons. It should be noted that the depression of the nerve elements is more pronounced in the caudal direction than in the cranial direction. The depressed state of reflex activity of each section of the spinal cord depends on its proximity to the section of the brain.For example, if the spinal cord is cut in the cervical region, then the state of shock manifests itself on the front (upper) limbs more than on the hind (lower) limbs. There are a number of opinions regarding the nature of the shock. For the first time, the German physiologist Goltz (1896) expressed the opinion that the cause of shock is the inhibition of the nerve elements of the spinal cord caused by trauma. However, the English physiologist Sherrington (1906), who carefully studied the phenomenon of spinal shock, showed that shock cannot be explained by inhibition of the spinal cord structures.
The following facts can be cited in favor of Sherrington’s opinion:
- If the shock were inhibition of the structures of the spinal cord, then it would be detected in the cranial region with the same force as in the caudal one.
- After cutting the spinal cord under the medulla oblongata, a vivid picture of spinal shock develops.
If, after the reflex activity of the spinal cord is restored, the spinal cord is cut again below the previous level of the cut, then the phenomena of spinal shock do not appear.Taking into account the two above facts, the unequal duration of shock in different representatives of the animal world, as well as electrophysiological studies of spinal shock, in recent years a modern view of the nature of spinal shock has been formulated. Its essence is as follows: one of the main factors causing the phenomenon of shock when the spinal cord is cut is the rupture of long pathways descending from the brain, which leads to a sudden cessation of diverse afferentation from the structures of the brain to the centers of the spinal cord.Cessation of the flow of afferentation from the brain upsets (inhibits) the reflex activity of the spinal cord. Another factor also plays a role in the origin of the shock. The transection of the brain causes a rather long-term mechanical irritation of the spinal cord. Not only nerve cells are irritated, but also ascending and descending pathways, which ultimately leads to inhibition of reflex activity. After the phenomena of spinal shock disappear, the following reflexes of the spinal cord can be observed: protective reflexes, stretching reflexes, reflexes of antagonistic muscles, visceromotor and autonomic reflexes.The frog’s defense reflexes usually manifest themselves in withdrawing the paw with weak irritation of the skin receptors; with more severe painful irritation, the animal can be observed “running away”. Stretch reflexes manifest as muscle shortening as it stretches. The reflexes of the antagonistic muscles underlie the locomotor acts of walking and running. Visceral reflexes are manifested when the afferent fibers of the internal organs are irritated. Vegetative reflexes are manifested mainly when preganglionic sympathetic fibers are excited in response to the excitation of sympathetic and somatic sensitive cells.With damage to the upper cervical spinal cord, paralysis of the cervical muscles, diaphragm, anesthesia in the neck and occiput occurs. With the defeat of the cervical thickening, paralysis of the forelimbs develops, their anesthesia. When the thoracic region is affected, paresis (partial paralysis) of the muscles of the back, chest or abdominal wall occurs with segmental anesthesia. With the defeat of the lumbar thickening, paralysis of the hind limbs, anesthesia in the lower limbs, and disorder of the pelvic organs are observed. Lesion of the cone (cauda equina; CI-III segments) causes anesthesia in the perineal region and disorder of the pelvic organs.
The following most important autonomic centers are located in the spinal cord:
- In the lateral horns of the thoracic spinal cord are the vasomotor centers and the centers of the sweat glands.
- At the level of the cranial lumbar segments and in the third, fourth and fifth sacral segments, the centers of urination and defecation are laid.
- At the level of the sacral segments are the centers of erection and ejaculation.
- At the level of the VII cervical – IV lumbar segments are the centers of the sympathetic nervous system.
- At the level 1-III – sacral segments of the spinal cord are the centers of the parasympathetic nervous system. With the defeat of the centers of urination, paralysis of the sphincter and detrusor occurs, as a result of which urine is constantly released drop by drop. With the defeat of the centers of defecation, incontinence of feces and gases occurs, there is no anal reflex. With the defeat of the centers of sexual reflexes, erection and ejaculation are disturbed.
Segmental structure of the brain
Integrative functions of the medulla oblongata
The medulla oblongata is the lowest part of the brain, located between the pons varoli and the spinal cord.The medulla oblongata is of great functional importance.
Its main functions are as follows:
– Conducting function.
– The medulla oblongata includes a number of important, vital reflex centers.
– The centers of some cranial nerves are located in the medulla oblongata.
– The nerve centers of the medulla oblongata are involved in the regulation of muscle tone and some setting reflexes.
– The medulla oblongata contains the reticular formation.
Characterizing the conduction function of the medulla oblongata, it should be noted that it contains fibers that carry impulses from various structures of the brain to the periphery and from the periphery to the structures of the brain. In the medulla oblongata, there are fibers of the reticular formation. The paths of the ascending and descending directions are described above. Of the vital reflex centers, the respiratory and vasomotor (vasomotor) centers should be mentioned first of all. Thanks to the studies of several generations of Russian and foreign physiologists, the position that the leading role in the regulation of respiration belongs to the structures of the medulla oblongata has become generally accepted.The respiratory center is considered as a set of respiratory neurons, the activity of which is synchronous with the phases of the respiratory cycle. In accordance with the nature of the activity pattern, respiratory neurons are divided into six main types (Bianchi et al., 1995): early inspiratory, inspiratory with an increasing pattern of activity, late inspiratory, post-inspiratory, expiratory with an increasing pattern of activity, pre-inspiratory.
Respiratory neurons are concentrated mainly in five functionally different areas of the respiratory center:
- Dorsal respiratory group of neurons located in the ventrolateral part of the nucleus of the solitary tract.
- Rostral (inspiratory) part of the ventral respiratory group, located in the area of n. Ambiguus .
- Caudal (expiratory) part of the ventral respiratory group, located in the area of n. Retroambigualis .
- Pre-Betzinger complex located in the rostral part of n. ambiguus and ventrolateral region of the reticular formation caudal to n. retrofacialis and rostral n. lateralis reticularis (3 mm rostral obex, 3.2-4 mm lateral to the midline).This complex contains a unique variety of types of respiratory neurons. A large number of propriobulbar neurons are present here, there are bulbospinal neurons and cranial motor neurons, neurons involved in the generation of the respiration rhythm (pre-inspiratory and neurons with pacemaker properties), pre- and post-inspiratory neurons have been identified.
- Betzinger complex. This section of the respiratory center is located in the area n. retrofacialis.
Most of the cells of the Betzinger complex are expiratory neurons.Such neurons form monosynaptic inhibitory projections in the direction of the bulbospinal inspiratory neurons of the dorsal and ventral respiratory groups, and the caudal group of suture nuclei. The Betzinger complex also contains pacemaker neurons. At the beginning of the 19th century, Flourans (1824) expressed the opinion that the medulla oblongata plays the most important role in the regulation of blood circulation. In 1853 Budg and then in 1855 Shiff established that cutting the spinal cord under the medulla oblongata caused a sharp drop in blood pressure.In this regard, they concluded that the center regulating the amount of blood pressure is located in the medulla oblongata. The most fundamental studies on the analysis of the location of the cardiovascular center were carried out by Ya.A. Dedyulin (1868) on cold-blooded animals and Dittmar (1873) and F.V. Ovsyannikov (1871) on warm-blooded animals.
Particularly noteworthy are the works of F.V. Ovsyannikov. He found that in the area, the upper border of which is located 1-2 mm caudal to the quadruple, and the lower one is 4-5 mm rostral to the penis, there is a center that regulates the activity of the cardiovascular system.With the destruction of this area, an irreversible pronounced decrease in blood pressure occurs. Further studies of the localization of the vasomotor center showed the following. Lafon (Laffont, 1880) established that with local mechanical stimulation of various parts of the bottom of the fourth ventricle of the medulla oblongata, pressor and depressor reactions can occur. S.A. Brushtein (1901) showed that the vasomotor center, which causes pressor and depressor reactions, is located under the bottom of the rhomboid fossa, in its middle and lower third, in the reticular formation of the medulla oblongata.The concept of localization in the medulla oblongata of two vasomotor centers (the pressor center, which increases pressure, and the depressor center, which lowers the pressure) was developed in the works of Beilis (1893-1923). Porter (Porter, 1915) believed that there are two centers in the medulla oblongata: vasotonic, which controls vascular tone, and vasoreflex, which integrates cardiovascular reflex reactions. Ranson and Billingsley (1916) suggested that the pressor center is located in the forea inferior region, at the ala cineria apex, and the depression center is located in the area postrema, somewhat lateral to the obex.Different localization of the pressor and depressor centers is shown in the works of many researchers (Scott, Roberts, 1923; Wang, Ranson, 1939; Sklyarsky, 1941, etc.). In 1946, Alexander expressed the opinion that there is only one center in the medulla oblongata – the vasomotor center. It is a single functional formation with efferent pathways that run as part of the dorsolateral cords of the spinal cord.
The above ideas about a clear differentiation of the pressor and depressor structures of the medulla oblongata have not been confirmed in the works of many researchers.Currently, it is believed that the main vasomotor center is located in the medulla oblongata, which maintains vascular tone and provides reflex regulation of blood pressure. This opinion was first substantiated by F.V. Ovsyannikov in 1871. He showed that the destruction of only the medulla oblongata causes an irreversible “catastrophic” drop in blood pressure. But a clear anatomical localization of the vasomotor center in the medulla oblongata has not yet been established.It is possible that the neurons that regulate the level of blood pressure are diffusely located in the medulla oblongata.
There is also an opinion that the vasomotor center consists of three main types of neurons: pressor, depressor and cardioinhibitory. Pressor neurons (group, zone) increase blood pressure as a result of an increase in peripheral vascular resistance and an increase in cardiac output; depressor neurons (group, zone) lower blood pressure, causing inhibition of tonic discharges of vasoconstrictors; cardio-inhibiting neurons (group, zone) decrease the amount of cardiac output by stimulating the cardiac center of the vagus nerve.In the structures of the medulla oblongata are located: the digestive center, consisting of several components, the centers of salivation, sweating, centers of protective respiratory reflexes, vomiting, regulation of carbohydrate metabolism.
Regarding the center of carbohydrate metabolism, it should be noted that for the first time in 1849, the French physiologist Claude Bernard performed an experiment called “sugar injection”, and this laid the foundation for studies of the bulbar regulation of carbohydrate metabolism. It was found that irritation of the posterior part of the dorsal nucleus of the vagus nerve causes hyperglycemia and glycosuria, and irritation of the anterior part of the nucleus leads to a decrease in blood and urine sugar.On this basis, it was suggested that there are two centers in the medulla oblongata, one of which increases the sugar content in the blood and urine, the other lowers it. In the medulla oblongata is the bulbar section of the parasympathetic nervous system. It is represented by cell groups of the nuclei of the facial, hypoglossal, glossopharyngeal and vagus nerves. Parasympathetic fibers of the facial nerve innervate the lacrimal gland, submandibular and sublingual salivary glands. The parasympathetic fibers of the vagus nerve innervate the thyroid and thymus glands, bronchi, lungs, heart, esophagus, stomach, small and large intestines up to and including the transverse colon, liver and kidneys.Parasympathetic fibers of the glossopharyngeal nerve innervate the submandibular and parotid salivary glands.
The medulla oblongata contains the nuclei of many cranial nerves. VIII pair – the auditory nerve (n. Acusticus). The nuclei of this nerve lie at the bottom of the rhomboid fossa. They consist of two roots of different function: n. cochlearis, the cochlear nerve, is the auditory nerve; n. vestibularis, the vestibular nerve, is the center of proprioceptive sensitivity that regulates body balance and coordination of movements.IX pair – glossopharyngeal nerve (n. Glossopharyngeus) – mixed nerve, consisting of motor and sensory (mainly taste) fibers.
The motor nucleus of this nerve is located in the medulla oblongata. The flavoring fibers originate from ganglion jugulare et ganglion petrosum. The glossopharyngeal nerve conducts gustatory afferentation from the receptors of the mucous membrane of the posterior third of the tongue and the soft palate with its anterior arches. X pair – vagus nerve, n. vagus is a mixed nerve.It contains sensory and motor fibers. Motor fibers originate in the dorsal nucleus (n. Dorsalis) and the ventral nucleus (n. Ambiguus). They innervate the palatine muscles, the stylopharyngeal muscles, the muscles of the larynx, as well as all the organs of the chest and abdominal cavities. Sensory fibers of the vagus nerve originate from the cells of ganglion jugulare et ganglion nodosum. Sensory fibers of the vagus nerve conduct afferentation from the receptors of all internal organs, as well as from the receptors of the skin of the external auditory canal and the auricle.XI pair – accessory nerve, n. accessorius Willissii. Some of the fibers of this nerve exit from the caudal part of the medulla oblongata. Most of the cells that give rise to the accessory nerve are located in the cervical spinal cord. Another part of the cells is adjacent to the motor nucleus of the vagus nerve. The accessory nerve consists only of motor fibers. It innervates two muscles: m. sterno-cleido-mastoideus et m. trapezius. XII pair – hypoglossal nerve, n. hypoglossus. The nerve contains only motor fibers.It innervates the muscles of the tongue.
One of the structures of the medulla oblongata is the paired nucleus of Deiters, which, along with the red nuclei and tubercles of the quadruple, takes part in the regulation of muscle tone. This participation is most clearly manifested in “decerebrational rigidity”. Decerebration is the separation of a part of the brain from another. Decerebration was first performed in 1896 by the English physiologist Charles Sherrington. In the case of “decerebrational rigidity”, the brain is usually cut between the anterior and posterior tubercles of the quadruple, less often between the posterior tubercles of the quadruple and the medulla oblongata.After the operation, as the anesthesia weakened, decerebral rigidity develops. It manifests itself in the fact that all limbs unbend and convulsively stretch, the head and neck rise up, the tail rises up and the back “arches”. During the rigid state, the flexor muscles also contract, however, the mechanical action of the extensors on the joints is stronger than the flexors, so the extensor position is maintained. It should be noted that during a strong rigid state, the flexor muscles of the limbs experience strong tonic inhibition.Over time, the decerebral extensor tone weakens and may change to a general flexion tone. The mechanism of decerebrational rigidity is as follows: the Deiters nuclei of the medulla oblongata are under the constant inhibitory influence of the red nuclei of the midbrain. The red nuclei not only have a constant tonic, inhibitory effect on the Deiters nuclei, but also provide an even distribution of afferentation between the flexor and extensor muscles. After the separation of the red nuclei from the Deiters nuclei, the inhibitory and other influences of the red nuclei on the Deiters nuclei cease, which leads to the development of extensor hypertonicity.The cerebellum (through the fastigial nucleus) also has an inhibitory effect on the Deiters nuclei, so removal of the cerebellum leads to an increase in decerebrational rigidity. On decerebrate animals, posture adjusting reflexes, phase reflexes of sneezing, “walking” can be observed. Many complex centers are located in the reticular formation of the medulla oblongata.
Studies have shown that certain areas of the medulla oblongata affect the motor neurons of the spinal cord. These bulbar neurons, in turn, are influenced by the overlying regions of the brain.In the ventrolateral part of the reticular formation of the medulla oblongata, a group of cells has been identified that has an inhibitory effect on spinal reflexes. In the dorsal part of the reticular formation of the medulla oblongata, there is a group of cells that provide for the implementation of spinal reflexes. One of the nuclei of the reticular formation, the giant cell nucleus, deserves special attention. The work of the staff of the Department of Human and Animal Physiology of the Samara State University (N.A. Merkulova, A.N. Inyushkin, V.Belyakova, R.A. Zainulina) led to the following conclusion: the respiratory effects of the sensorimotor cortex of the brain, cerebellum, as well as structures of the extrapyramidal system are realized through the reticular giant cell nucleus. This nucleus, with a certain degree of probability, can be regarded as a collector of diverse afferentation, which comes to the respiratory center from various suprabulbar parts of the brain.
Integrative functions of the hindbrain
The hindbrain consists of two sections: the pons varoli and the cerebellum.
The Varoliev bridge, or simply the bridge (pons), is a thick white shaft on the side of the base of the brain, bordering caudally with the rostral end of the medulla oblongata, and cranially with the legs of the brain.
The nuclei of the V-VIII pair of cranial nerves are located in the pons.
V pair – abducens nerve ( n. Abducens ), the nucleus of this nerve is located in the cranial part of the pons. This nerve innervates only one muscle – the muscle that takes the eye outward.
VI pair – the trigeminal nerve ( n. Trigeminus ), which consists of motor and sensory fibers. Sensory fibers innervate the cranial region of the head, the skin of the forehead and upper eyelid, the conjunctiva of the eyeball, the cornea and the iris, and the mucous membrane of the frontal sinus and upper part of the nose. The trigeminal nerve innervates the skin, the lower parts of the nose, upper jaw and palate, as well as the upper and lower teeth, the mucous membrane of the cheeks, lower jaw, floor of the mouth, tongue; supplies the anterior two-thirds of the tongue with taste fibers.
VII pair – facial nerve (n. Facialis). This nerve innervates the muscles of the front of the muzzle. Irritation of the vestibular nuclei of the pons varoli causes an increase in blood pressure, an increase in peripheral vascular resistance and a decrease in cardiac output. Along with hemodynamic changes during electrical stimulation of various parts of the vestibular nuclei of the pons, a variety of changes in respiration are noted: a decrease or increase in the depth of breathing, an increase or decrease in respiration.On the basis of these data, it can be assumed that the varoli bridge is involved in the regulation of respiration, vascular tone and heart activity.
The cerebellum is an outgrowth of the bridge. It appears at the early stages of vertebrate phylogenesis. The cerebellum can be different in size – from a small “lump” to a large formation. In some fish it reaches a considerable size, but in amphibians and reptiles it is small. The cerebellum is significantly developed in mammals, animals and humans.A. Larcel divides the entire surface of the cerebellum into several sections, mainly depending on the phylogenetic age.
These departments are as follows:
- Architserebellum (ancient cerebellum) is represented by a small clumpy-nodular lobule.
- Paleocerebellum (old cerebellum) includes the anterior lobe, the area of the worm corresponding to the anterior lobe, pyramids, uvula, paraflocular lobe.
- Neocerebellum (new cerebellum) includes the hemispheres and the part of the worm that is located caudal to the area of the worm corresponding to the anterior lobe.
Noteworthy is the structure of the cerebellar cortex. It has a distinct three-layer structure.
The first surface layer is molecular. Consists of basket-shaped and star-shaped cells.
The second layer – granular – is represented by Purkinje cells, which are found only in the cerebellum.
The third layer – granular – consists of granular and Golgi cells.
According to Fanarjian, there are five types of cells in the cerebellar cortex:
- Purkinje cells,
- basket cages,
- star cages,
- Golgi cells,
- granular cells.
According to Schmid, in the cerebellar cortex, along with the aforementioned types of cells, there is a sixth type of cells – Lugaro cells.
The cerebellum has widely developed connections, in essence, with all structures of the brain, as well as with the spinal cord.
The main afferent pathways of the cerebellum are as follows:
- Dorsal spinal cord.
- Ventral spinal cord, which carries proprioceptive afferentation from the back of the body.
- Rostral spinal cord tract conducting proprioceptive afferentation from the anterior part of the body.
- Dorsal-olive-cerebellar tract.
- Cerebro-cerebellar connections. According to these connections, afferentation enters the cerebellum from the “motor” region of the cerebral cortex.
- Cortico-reticulo-cerebellar pathway.
- Olive-cerebellar tract. This pathway conducts afferentation from the olive region to the cerebellum.
- The vestibulo-cerebellar pathway transmits afferentation from the vestibular nuclei to the cerebellum.
- Rubro-cerebellar connections transmitting afferentation from the red nuclei to the cerebellum.
- Reticulo-cerebellar connections conduct afferentation to the cerebellar cortex from the lateral, paramedial nuclei of the medulla oblongata, from the nucleus of the pons tegum, from the reticular giant cell nucleus.
- The pathways from the structures of the basal ganglia to the cerebellum were identified.
All afferent pathways end in three types of fibers. Mossy fibers come from the nuclei of the pons and end in the granular layer of the cerebellar cortex.Liana-like, or climbing, fibers come from the lower olives. These fibers represent a unique component of the organization of the cerebellar cortex. One liana-shaped fiber makes synaptic contact with only one Purkinje cell.
At the level of the Purkinje cell layer, these fibers lose myelin and run parallel to the body and dendrites of Purkinje cells. Liana-shaped fibers, passing through the granular layer, give off collaterals to the synapses of granular cell dendrites, soma of Golgi cells, Lugaro cells.The third afferent system is monoaminoergic connections. This system includes noradrenergic, serotonergic, and dopaminergic fibers. The source of noradrenergic fibers is the blue spot. Fibers from the blue spot go to all the nuclei of the cerebellum, pass through the granular layer, and then braid the Purkinje cells and enter the molecular layer. Dopaminergic fibers enter the cerebellum from the lining of the midbrain. These fibers form synaptic contacts with Purkinje cells and granular cells.The source of serotonergic fibers are the nuclei of the medulla oblongata, midbrain and pons.
The main efferent pathways of the cerebellum are as follows. It has been established that the axons of Purkinje cells, which are inhibitory neurons, constitute the only efferent pathway. But the fibers that make up this efferent pathway carry out predominantly, if not exclusively, inhibitory influences to numerous structures of the central nervous system: the spinal cord, to the nuclei of the medulla oblongata, midbrain and diencephalon, the centers of the extrapyramidal system, the “motor” region of the cerebral cortex.It should be noted that mossy fibers carry out excitatory afferentation. Liana-shaped fibers, mediated through Purkinje neurons, partly through basket and stellate neurons, conduct inhibitory afferentation. Thus, the cerebellum can have a variety of effects – excitatory and inhibitory on various parts of the central nervous system.
An important functional role is played by the cerebellar nuclei.
The following paired nuclei are located in the white matter of the cerebellum:
tent kernels, corky, spherical and toothed kernels.
The noted nuclei have connections with numerous structures of the central nervous system (spinal cord, medulla oblongata, pons, midbrain and diencephalon, motor area of the cerebral cortex). Various methods are used to study the functions of the cerebellum.
The main ones are: the method of clinical observation, the method of extirpation (removal), irritation, electrophysiological methods. Removal of the cerebellum made it possible, first of all, to reveal its special role in the integration of information necessary for the regulation of motor reactions (Luciani, 1893; Levandovsky, 1907; Orbeli, 1935; Aleksanyan, 1948; Karamyan, 1956, 1970; Moruzzi, 1958; Arshavsky, 1976; Grigoryan , 1976, etc.).
The main functions of the cerebellum in the regulation of motor activity have been established:
- regulation of posture and muscle tone;
- correction of slow targeted movements;
- Ensuring the execution of fast, targeted movements.
After removal of the cerebellum, the following disorders (symptoms of impaired cerebellar function) are detected:
- Asynergy – the lack of sending the proper number of impulses to the various muscles performing the movements.This leads to the fact that movements are performed either in excess or insufficient volume. There is an irregular gait with widely spaced legs and an excessive volume of motor reactions. This symptom was first described by Babinsky in 1899.
- Astasia – oscillatory movements of the head and trunk. The tremor increases during physical activity; at rest, the tremor disappears.
- Ataxia – violation of the magnitude, strength, speed, direction of motor reactions.Movements lose smoothness and stability, dysmetria develops (incorrect distance estimation).
- Hypotension – decreased muscle tone. More often, wave-like changes in tone develop: hypotension is replaced by an increase in muscle tone, then a decrease in muscle tone occurs again, and so on.
- Nystagmus – involuntary movements of the eyeballs.
- Dizziness.
- Asthenia – fatigue.
The variety of symptoms that develop after removal of the cerebellum is apparently explained by the abundance of efferent connections of this structure with various parts of the central nervous system. Perhaps the cerebellum coordinates the work of various structures into a single system that determines the adequacy and perfection of motor reactions. There are also other opinions about the role of the cerebellum in the regulation of motor reactions. So, Winner (1961) believes that the cerebellum plays the role of a system that prevents the occurrence of oscillatory modes when performing movements.Rukh (1951) considers the cerebellum as a kind of block that provides a comparison of the commands sent by the cortical centers of regulation of movements with the real course of their implementation. Based on this comparison, the cerebellum corrects the work of the executive motor centers. Breitenberg (1967) believes that the cerebellum provides an accurate measurement of the time intervals between afferent signals.
Since the 30s of the twentieth century, systematic studies have been undertaken by L.A. Orbeli, dedicated to the role of the cerebellum in the regulation of autonomic functions.The role of the cerebellum in the regulation of many autonomic functions has been established: digestion, respiration, vascular tone, heart activity, thermoregulation, metabolism, and others.
At the Department of Human and Animal Physiology, Samara State University, studies were carried out to analyze the importance of the cerebellum in the regulation of respiration (N.A. Merkulova, A.N. Inyushkin, V.I.Belyakov). Comparative analysis of respiratory reactions caused by electrical stimulation of various parts of the cerebellar structures made it possible to reveal the inhibition of the rhythm-generating function of the respiratory center.It was found that the regions of the rat cerebellum, most active in relation to the regulation of respiration, overlap topically with the regions of the motor representation of the vibrissal apparatus and the forelimbs. The GABAergic neurotransmitter system is involved in the mechanism of realization of the respiratory influences of the cerebellum. The ambigual and reticular giant cell nuclei of the medulla oblongata are the “targets” for the implementation of the respiratory reactions of the cerebellum.
Integrative functions of the midbrain
The midbrain includes the legs of the brain and the quadruple.The brain stem is a massive cord of longitudinal nerve fibers extending from the anterior edge of the pons to the mass of the cerebral hemisphere. Due to the divergence of the legs between them, a fossa is formed, the bottom of which is dotted with numerous holes that serve to pass the vessels from the base of the brain into the depths of the cerebral hemispheres.
The dorsal part of the midbrain is formed by a quadruple plate overlying the sylvian aqueduct. The plate has four elevations: two anterior ones form the anterior colliculus (anterior tubercles of the quadruple), two posterior elevations form the posterior colliculus (posterior tubercles of the quadruple).
At the level of the anterior hillocks of the quadruple, at the bottom of the Sylvian aqueduct lies the nucleus of the III pair of cranial nerves of the oculomotor nerves ( n. Oculomotorius ).
At the level of the posterior hillocks of the quadruple, also at the bottom of the Sylvian aqueduct, lies the nucleus of the IV pair of cranial nerves of the trochlear nerves ( n. Trochlearis ). In the pedicle of the brain, a base and a tectum are distinguished. The border between the base and the tire is formed by the Semmering black substance ( substantia nigra Soemmeringi ).In the operculum of the cerebral peduncle lies a red nucleus ( n. Ruber ).
Analysis of the morphological features of the midbrain makes it possible to distinguish the following main structures that provide many important functions: the nucleus of the oculomotor nerve, the nucleus of the trochlear nerve, the red nucleus, the substantia nigra.
Giving a general description of the functions of the midbrain, it should be noted:
- conductive function;
- The presence in the midbrain of the centers of many reflex reactions, especially locomotor ones.
90,000 Brain Areas – Learn more about the different parts of your brain
What is our brain made of? The brain is one of the most complex organs of the human body. It consists of various parts or structures, each of which has its own function, but they work together and in a coordinated manner through the thousands of connections that form between them and all other parts of our body. Below will be shown the structure of the brain, its region and the function of each zone.
The structure of the brain
The central nervous system consists of the brain and spinal cord.
- The brain is the main part of the central nervous system and is located in the skull.
- The spinal cord is a long, whitish cord located in the spine that connects the brain to the entire body. It acts as a kind of information highway between the brain and the body, transmitting information from the brain to the body.
So the brain and the brain are not the same thing. To understand the difference between the brain and the brain, one should study how the CNS (central nervous system) of the embryo develops.In general terms, during development , the human brain is divided into three different “brains” according to their level of phylogenetic development: the rhomboid brain (rhombencephalon), mesencephalon (“midbrain”), and proencephalon (“forebrain”).
ROMBOID BRAIN: The oldest and least developed brain structure found in all vertebrates. The structure and organization of the diamond-shaped brain is the simplest. Responsible for regulating basic survival functions and controlling movement.Damage to this part of the brain can lead to death or serious damage. Located in the upper part of the spinal cord and consists of several sections:
- Medulla oblongata or bulb : helps control automatic functions such as breathing, blood pressure, heart rate, digestion … etc.
- Varoliyev bridge or bridge : the part of the brain stem located between the medulla oblongata and midbrain. It connects the spinal cord and medulla oblongata to the upper cortex and / or cerebellum.It controls the automatic functions of the body, and also regulates consciousness and levels of arousal (anxiety), sleep.
- Cerebellum : Located under the occipital lobes of the cerebral hemispheres, it is the second largest structure in the brain. The cerebellum integrates all the information coming from the senses and the motor area of the brain, and therefore its main function is to control movement. It also controls posture and coordination of movements, which allows us to move, walk, ride a bicycle… Damage to this region leads to problems associated with movement, coordination and postural control, as well as impairments of a number of higher cognitive processes.
MEZENCEPHALON or MEDIUM BRAIN – is a structure that connects the back of the brain with the front, directing motor and sensory impulses between them. Its correct functioning is necessary for the implementation of conscious actions. Injuries to this part of the brain cause a number of movement disorders, such as tremors, rigidity, and strange movements…
FRONT BRAIN or PROSENCEPHALON: is the most developed and evolved part of the brain with the most complex organization. Consists of two main divisions:
- Diencephalon: is located inside the brain and consists of such important structures as the thalamus and hypothalamus.
- Thalamus: is a kind of transmission station of the brain: it transmits most of the perceived sensory signals (visual, auditory and tactile) and makes them possible for other parts of the brain to process them.Also involved in motor control.
- Hypothalamus: This gland located in the central base of the brain plays a critical role in regulating emotions and many other bodily functions such as appetite, thirst and sleep.
- Terminal or large brain: is known as the brain that covers the entire cerebral cortex (a thin layer of gray matter collected in folds that form the grooves and gyrus), the hippocampus and the basal ganglia.
Anatomy and function of the brain
In this section, we will look in detail at the anatomy of the brain and the functions of its departments.
BASAL GANGLES: subcortical neural structures responsible for motor functions. They receive information from the cortex and brain stem, process it and re-project it into the cortex, medulla oblongata and the brain stem, ensuring coordination of movements. They consist of several departments:
- The caudate nucleus is a nucleus in the shape of the letter C, involved in the control of conscious movements, as well as in the processes of learning and memory.
- Shell
- Pallidum
- Tonsil, which plays a key role in controlling emotions, especially fear.The amygdala helps to store and classify memories triggered by emotions.
HIPPOCAMP: A small subcrustal structure in the shape of a seahorse. Plays a critical role in the formation of memory – both in the classification of information and the organization of long-term memory
BRAIN CORTEX: A thin layer of gray matter collected in folds that form grooves and convolutions that give the brain a characteristic appearance. The convolutions are separated by grooves and cerebral grooves, the deepest of which are called slits.The cortex is divided into two hemispheres, right and left, separated by an interhemispheric fissure and interconnected by the corpus callosum, through which information is transmitted from one hemisphere to another. Each hemisphere controls one side of the body, while control is asymmetric: the left hemisphere controls the right side, and the right one controls the left side of the body. This phenomenon is called brain lateralization.
EACH HEMISPHERE, IN ITS ORIGIN, DIVIDED INTO 4 SHARES: these lobes are limited by four cerebral grooves (central or Roland’s groove, lateral or Sylvian groove, parieto-occipital groove and cingulate groove
5 lobe lobe): 9000 the largest lobe of the cerebral cortex.Located in front of the skull, behind the forehead. Extends from the front to the Roland furrow. This is the center of command and control of the brain, the conductor of the orchestra. It is closely related to executive functions (Miller, 2000; Miller and Cohen, 2001), i.e. responsible for planning, reasoning, problem solving, judgment, impulse control, as well as regulating emotions such as empathy and generosity, behavior. Squire, L.R. (1992) Memory and the hippocampus: a synthesis from findings with rats, monkeys and humans. Psychol Rev, 99, pp. 195-231. Miller, E. K. (2000). The prefrontal cortex and cognitive control. Nat Rev Neurosci, 1 (1), 59-65. Miller, E. K. y Cohen, J. D. (2001). An integrative theory of prefrontal cortex function. Annu Rev Neurosci, 24, 167-202. Kosslyn, S.M. (1994) Image and brain: thre resolution of the imaginery debate.Cambridge, Mass; MIT Press. Complexity: one Complexity: one Complexity: four Complexity: 2 Complexity: one Complexity: 3 Complexity: 2 Complexity: four Complexity: one Complexity: one Complexity: one The nervous system is a system of specialized cells responsible for maintaining the body’s internal environment and coordinating the body’s interaction with the outside world – from controlling basic functions such as heart rate and breathing, to moving to avoid danger. The vertebrate nervous system is divided into two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS).The CNS includes the brain, spinal cord, and retina – the sensory tissue of the visual system. The PNS contains sensory receptor cells for all other sensory systems, such as sensory receptors in the skin, as well as nerves that carry information between the CNS and the rest of the body. In addition, part of the CNS and PNS contribute to the autonomic nervous system (also known as the visceral locomotor system). The autonomic nervous system controls smooth muscles, heart muscles, and glands, which regulate involuntary actions such as digestion. The vertebrate brain is mainly divided into the brain, cerebellum and brainstem. The brain is the largest, most prominent part of the brain, which is divided into the left and right hemispheres. Each hemisphere is further divided into four lobes: frontal, parietal, occipital, and temporal. The outer layer of the brain is called the cortex, which is involved in processing complex sensory information and most cognitive functions. Deeper within the brain are other critical components, including the hippocampus, hypothalamus, thalamus, and basal ganglia.The cerebellum (“small brain”) is located posterior to and below the brain and is responsible for coordinating muscle movement. The brain stem connects the brain to the spinal cord and has important centers for vital functions such as breathing and swallowing. The spinal cord lies below the brain and goes into the brainstem. It contains bodies of neuronal cells and axon bundles that connect the brain and various parts of the body. In addition to being an important channel for transmitting information, the spinal cord can perform some functions without the involvement of the brain, such as locomotion and other reflexes.PNS nerves transmit motor commands from the CNS to muscles and sensory information from receptor cells to the CNS for interpretation. In addition to the movement of skeletal muscles, nerves regulate the activity of internal organs, such as the lungs and intestines, through the sympathetic and parasympathetic divisions of the autonomic nervous system. The nervous system is made up of two main types of cells: neurons and glial cells. Neurons are the strongest link in the central nervous system – they are responsible for communicating with each other and transmitting information from the nervous system to the rest of the body.It is estimated that the human brain contains about 100 billion neurons and a staggering 100 trillion connections between them. They come in a variety of morphologies and perform a wide range of functions. Neurons use a set of neurochemicals and ions to communicate at connections called synapses. Another major cell type in the nervous system is part of a group called glial cells. They include a diverse group of cells that contribute to neuronal function and are roughly equal to the number of neurons in the brain.The main types of glial cells include astrocytes, microglia, oligodendrocytes, and ependymal cells of the central nervous system; Schwann cells and satellite cells are located in the PNS. The nervous system governs virtually every experience we have, and disruption from trauma, disease, genetics, or exposure to harmful chemicals can have serious consequences for health and quality of life. Mental illnesses that result from such consequences are surprisingly common throughout the world.Our deepening understanding of neurological and neurodevelopmental disorders continues to provide potential treatments and therapies for many who suffer from mental illness. The World Health Organization (W.H.O.) and the National Institutes of Mental Health (N.I.M.H) in the United States, among others, provide valuable resources for both studying these conditions and tracking their impact on society. Literature for additional reading Purves, Dale, George J.Augustine, David Fitzpatrick, Lawrence C. Katz, Anthony-Samuel LaMantia, James O. McNamara, and S. Mark Williams. “Neural Systems.” Neuroscience. 2nd Edition , 2001. [Source] Structure and function of the central nervous system. Biology, Human (grade 8): lessons, tests, assignments.
one. central nervous system
lung 2. Brain stem
lung 3. Sign brain regions
lung four. Brain zones
average five. Diencephalon functions
average 6. Cerebellum
average 7. Parts of the brain and their functions
average eight. The structure and function of the spinal cord
complicated nine. Human brain
complicated 10. Cortex
complicated eleven. Spinal cord
complicated What is a Nervous System?
eighteen.1: What is the nervous system?
Review
Parts of the nervous system
Cells of the nervous system
Mental health is a global problem
Neurology
Neurology is a science that studies all manifestations of the normal development and pathology of the human nervous system, as well as changes in the nervous system due to diseases of other organs and systems of the body or harmful external influences.
The main role of the nervous system is the perception and analysis of all signals outside the body and inside the body, further translation, processing and response. Thus, it is a watchdog who signals about trouble in the body or in the environment.
The human nervous system is subdivided into the central nervous system – the brain and spinal cord and the peripheral nervous system, i.e. all nerve fibers and nodes, plexuses of nerve fibers that are outside the central nervous system.The most common signal of unhappiness is pain.
The main symptoms to look out for are related to possible damage to the central nervous system, namely the brain, are:
- headache, numbness, dizziness, unsteadiness, asymmetry in the face, face distortion, squint, double vision, difficulty swallowing, choking, difficulty speaking, naughty tongue, awkwardness when performing normal movements, gait disturbance, weakness or numbness in an arm or leg, there may be convulsions, loss of consciousness, etc.d.
There may also be symptoms of a violation of higher mental functions:
- impaired memory, intelligence, irritability, tearfulness, rapid mood swings, depression, anxiety, obsessive thoughts, actions, reduced criticism of the situation, yourself, your illness, etc.
In diseases of the spinal cord, most often there is pain, weakness, and numbness in the trunk, arms, legs, cramps, muscle twitching, muscle atrophy, urinary disorders, constipation, etc.d.
The most common reason for patients to visit a neurologist at an outpatient appointment is the pathology of the peripheral nervous system. Most of them are patients with spinal pathology, this is the so-called vertebral neurology. This is due to the pathology of bone structures, discs, joints, muscle and tendon formations of the spinal column.
Today, damage to the intervertebral disc, vertebra, intervertebral joints and ligamentous apparatus, i.e.That is, the so-called degenerative-dystrophic lesions of the spine are called osteochondrosis.
There are many theories explaining the occurrence of degenerative changes in the spine. But along with them, there are factors that accelerate the development of osteochondrosis. You can get information on how to move properly, how to eat, a complex of preventive gymnastics and other recommendations from our specialists.
Appointment with a neurologist is carried out through a district therapist, via the Internet, self-recording.
Basic functions of an outpatient neurologist:
- consultation, diagnostics, medical assistance to patients with diseases of the nervous system
- examination of temporary disability
- selection and referral of patients to a hospital, day hospital, OVL, high-tech examination of the nervous systems
- dispensary observation of patients
- primary prevention of diseases of the nervous system
OUR TEAM
| GP No. 86 | Dzhurakulova Lola Mikhailovna neurologist of the first category | Even: 14.00 – 20.00 Odd: 08.00 – 14.00 Wednesday – dispensary day |
| GP # 86 | Shimanskaya Irina Borisovna neurologist | Daily: 09.00 – 15.00 Wednesday – dispensary day |
| GP # 86 | Zosina Maria Sergeevna neurologist | Even: 08.00 – 14.00 Odd: 14.00 – 20.00 Wednesday – dispensary day |
| p / o No. 57 | Ionochkina Marina Ivanovna Neurologist of the highest category | Even: 14.00 – 20.00 Odd: 08.00 – 14.00 Tuesday – dispensary day |
| p / o No. 57 | Amirov Jamal Gadzhimagomedovich neurologist | Even: 08.00 – 14.00 Odd: 14.00 – 20.00 Tuesday – dispensary day |
| p / o No. 57 | Mallakurbanova Dinara Alimuradovna neurologist | Daily: 08. |