Anatomy and physiology of the nervous system

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   The nervous system

Last medical review: January 2020

Diagram of the nervous system

The central nervous
system (CNS) is made up of the brain and spinal cord. The brain controls
most body functions, including awareness, movements, sensations, thoughts,
speech and memory. The spinal cord is connected to the brain at the brain stem
and is covered by the vertebrae of the spine. Nerves exit the spinal cord to both
sides of the body. The spinal cord carries signals back and forth between the
brain and the nerves in the rest of the body.

The peripheral
nervous system (PNS) is the part of the nervous system outside of the CNS.
It is made up of nerves and ganglia that send signals to and receive signals
from the CNS. The PNS is divided into the somatic nervous system and the
autonomic nervous system. The somatic nervous system controls body movements
that are under our control such as walking. The autonomic nervous system
controls involuntary functions that the body does on its own such as breathing
and digestion.

The autonomic nervous system is further divided into the
sympathetic and parasympathetic nervous systems. The sympathetic nervous system
prepares the body for situations that require strength and heightened awareness
or situations that arouse fear, anger, excitement or embarrassment. This is
called the fight-or-flight response. It causes the heart to beat faster, makes
you breathe quicker and more shallowly, dilates the pupils and increases
metabolism. The parasympathetic nervous system has a calming effect on the
body. It returns heart rate and breathing to normal, constricts the pupils and
slows down metabolism to conserve energy.

Diagram of the structure of the sympathetic nervous system

The sympathetic nervous system is made up of the following
parts.

The sympathetic chain is made of the sympathetic chain
ganglia that run in a chain from the head to the tailbone (coccyx), along both
sides of the spine. Ganglia are clusters of nerve cell bodies. The sympathetic
chain ganglia send messages to the head, neck, lower body (trunk) and
extremities during the fight-or-flight response.

The sympathetic chain ganglia affect spinal nerves and
nerves in the chest cavity. This helps to increase blood flow to skeletal
muscles and the brain, stimulate energy production for skeletal muscles to use,
release stored fats and stimulate the sweat glands. It also increases heart
rate, increases the pumping action of the heart and allows more air to move
into the lungs.

The 3 collateral ganglia are the celiac ganglion, the superior
mesenteric ganglion and the inferior mesenteric ganglion. They are in the abdomen
in front of the spine. The collateral ganglia send messages to organs in the
abdomen and pelvis.

The collateral ganglia affect nerves in the abdomen and
pelvis. Affecting these nerves lowers blood flow to organs, lowers activity in
the digestive system, stimulates the liver to release glucose to give the body
more energy, relaxes smooth muscle in the bladder wall and lowers urine
production.

The adrenal medulla is located in the centre of each adrenal
gland. These glands have specialized neurons. When these neurons are
stimulated, they release chemical messengers (called neurotransmitters) into
the blood that act as hormones.

The adrenal medulla is involved in releasing hormone-like
substances, such as epinephrine (adrenaline) and norepinephrine (noradrenaline),
into the blood. Cells that have receptors for epinephrine or norepinephrine
respond to these substances and take part in the flight-or-fight response.

• Meredith Irwin, MD

• Daniel Morgenstern, MD

• American Society of Clinical Oncology. Neuroblastoma. 2018: https://www.cancer.net/cancer-types/neuroblastoma-childhood/view-all.

• American Cancer Society. What is Neuroblastoma. 2018: https://www.cancer.org/.

• Martini FH, Timmons MJ, Tallitsch RB. Human Anatomy. 7th ed. San Francisco: Pearson Benjamin Cummings; 2012.

• PDQ® Pediatric Treatment Editorial Board. Neuroblastoma Treatment (PDQ®)–Patient Version. Bethesda, MD: National Cancer Institute; 2021: https://www.cancer.gov/types/neuroblastoma/patient/neuroblastoma-treatment-pdq.

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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:

1. Superior sagittal sinus

2. The confluence of sinuses

3. Transverse sinuses

4. Sigmoid sinuses

5. Jugular veins

6. Carotid arteries

7. Superior vena cava

8. 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.

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Figure

Illustration of peripheral and central nervous systems. Brain, spinal cord, nerves. Contributed by Chelsea Rowe

References

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Shipp S. Structure and function of the cerebral cortex. Curr Biol. 2007 Jun 19;17(12):R443-9. [PubMed: 17580069]

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Lanciego JL, Luquin N, Obeso JA. Functional neuroanatomy of the basal ganglia. Cold Spring Harb Perspect Med. 2012 Dec 01;2(12):a009621. [PMC free article: PMC3543080] [PubMed: 23071379]

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Rajmohan V, Mohandas E. The limbic system. Indian J Psychiatry. 2007 Apr;49(2):132-9. [PMC free article: PMC2917081] [PubMed: 20711399]

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Canedo A. Primary motor cortex influences on the descending and ascending systems. Prog Neurobiol. 1997 Feb;51(3):287-335. [PubMed: 9089791]

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Vrselja Z, Brkic H, Mrdenovic S, Radic R, Curic G. Function of circle of Willis. J Cereb Blood Flow Metab. 2014 Apr;34(4):578-84. [PMC free article: PMC3982101] [PubMed: 24473483]

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Fridriksson J, Fillmore P, Guo D, Rorden C. Chronic Broca’s Aphasia Is Caused by Damage to Broca’s and Wernicke’s Areas. Cereb Cortex. 2015 Dec;25(12):4689-96. [PMC free article: PMC4669036] [PubMed: 25016386]

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DeMaagd G, Philip A. Parkinson’s Disease and Its Management: Part 1: Disease Entity, Risk Factors, Pathophysiology, Clinical Presentation, and Diagnosis. P T. 2015 Aug;40(8):504-32. [PMC free article: PMC4517533] [PubMed: 26236139]

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Disclosure: Lauren Thau declares no relevant financial relationships with ineligible companies.

Disclosure: Vamsi Reddy declares no relevant financial relationships with ineligible companies.

Disclosure: Paramvir Singh declares no relevant financial relationships with ineligible companies.

Central Nervous System: Structure and Functions

Contents

• 1 Central Nervous System
  • 1.1 Functional Structure of the Central Nervous System
  • 1.2 Related Videos:
  • 1.3 Structure and Functions of the Brain 9 0008
  • 1.4 Anatomy and role of the spinal cord
  • 1.5 Somatic and visceral nervous system
  • 1.6 Sensory and motor functions of the CNS
  • 1.7 Limbic system and emotional processes
  • 1.8 Role of the CNS in the regulation of sleep and wakefulness
  • 1.9 Brain plasticity and learning
  • 1.10 Voice and speech control centers
  • 1.11 Role of the CNS in the process of coordination and balancing
  • 1.12 Influence of the C NS on the endocrine system
  • 1.13 Possible pathologies and diseases of the central nervous system
  • 1.14 Question-answer:
    • • 1.14.0.1 What is the structure of the central nervous system?
      • 1.14. 0.2 What are the functions of the central nervous system?
      • 1.14.0.3 What are the structures of the brain?
      • 1.14.0.4 How does the central nervous system regulate body movements?

The central nervous system is a complex structure of the body that includes the brain and spinal cord. It is responsible for the transmission and processing of information in the body, controls its functions and responds to external and internal stimuli. Knowledge of the work and characteristics of the central nervous system is key to understanding various diseases and diagnosing their treatment.

The central nervous system (CNS) is a complex of organs and tissues responsible for controlling and coordinating various body functions. It consists of the brain and spinal cord. The brain is in the cranium, and the spinal cord extends along the ridge inside the spinal canal. The structure of the CNS includes many nerve cells, nerve fibers, and glial cells, which play an important role in maintaining the structural and functional integrity of the system.

The brain is the main organ of the CNS, performing a number of important functions. It consists of various departments, each of which is responsible for certain activities. For example, the cerebral cortex is responsible for thinking, memory, speech, and perception, while deep brain structures control autonomic functions such as breathing, heart activity, and digestion.

The spinal cord, located inside the spinal canal, is the main transmission route for nerve impulses between the brain and the rest of the body. Information processing takes place in it, as well as reflex movements that can occur without the participation of consciousness.

The central nervous system plays an important role in the functioning of the body and is a complex and delicate system. Its structure allows for many functions, including information processing, regulation of motor activity, memory, emotions, and other aspects of human life.

Functional arrangement of the Central Nervous System

The Central Nervous System (CNS) is a highly organized system complex responsible for coordinating and regulating the work of various organs and body systems. It consists of the brain and spinal cord.

Neurons are one of the main functional elements of the central nervous system. Nerve cells form complex neural networks and transmit information in the form of electrical impulses. Synapses are points of contact between neurons that transmit electrical signals between them.

The central nervous system performs many functions, such as processing and analyzing information, regulating the internal environment of the body, controlling motor activity, implementing cognitive processes (perception, memory, thinking) and much more.

The structure of the CNS also includes protective elements – the meninges and cerebrospinal fluid, which protect the brain and spinal cord from damage and provide optimal conditions for their work.

The central nervous system plays an important role in the control and regulation of many processes in the body, ensuring its adaptation to external conditions and ensuring its survival and functioning.

Related videos:

Structure and functions of the brain

The brain is the largest and most complex structure of the central nervous system. It consists of various parts, each of which performs certain functions, ensuring the work of the whole organism.

The main structural components of the brain are the cerebrum, cerebellum, diencephalon and medulla oblongata. The brain consists of two hemispheres, left and right, which are responsible for thinking, speech, emotions, and auditory processing. The cerebellum controls motor coordination, while the diencephalon processes additional information about vision and hearing. The medulla oblongata is responsible for automatic bodily functions such as breathing and heartbeat.

The functions of the brain include processing information from various sensory organs (vision, hearing, smell, etc. ), control over movements, thinking, memory, regulation of emotions and coordination of other body systems. There are many neurons in the brain that exchange information and form complex networks that provide all these functions.

To ensure the normal functioning of the brain, it needs a constant supply of blood and oxygen. Poor blood supply or damage to brain structures can lead to dysfunction and various neurological diseases. Therefore, it is important to maintain health and take care of the proper functioning of the brain.

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Anatomy and role of the spinal cord

The spinal cord is one of the main parts of the human central nervous system. It is located in the spine and extends from the base of the head to the lumbar spine.

The spinal cord consists of many nerve cells – neurons, which form two sections: the anterior and posterior horns. The anterior horns contain motor neurons responsible for transmitting signals from the brain to the muscles and glands. The posterior horns contain sensory neurons that relay information from the senses to the brain.

The spinal cord plays a key role in the transmission of nerve impulses. It is a kind of “switch” between the brain and the body. The brain receives signals from the sense organs, and the spinal cord transmits messages from the brain to the muscles and glands, coordinating and controlling their work.

In addition, the spinal cord is responsible for the regulation of some automatic functions such as respiration, cardiac activity, intestinal peristalsis and urination. It also plays an important role in the processing and storage of information, allowing us to remember and recall various events and knowledge.

Thus, the anatomy of the spinal cord and its role in the human body are the main components of its nervous system. Thanks to the spinal cord, we can sense the world around us, control the movements of the body and maintain the vital functions of the body. This makes it an indispensable element of our body.

Somatic and visceral nervous system

Somatic nervous system is the part of the central nervous system responsible for controlling the movements and sensations of the outside world. It consists of peripheral nerves that transmit signals from the skin, muscles and stem ganglia to the spinal cord and brain, as well as neurons of the brain itself that control motor acts.

The visceral nervous system includes a network of nerve fibers and cells that controls the functions of internal organs. It regulates the activity of the heart, lungs, digestive system and other organs. Unlike the somatic nervous system, which controls conscious movements, the visceral nervous system operates automatically, without our conscious control.

Input signals from the internal organs enter the visceral nervous system through special sensors – receptors located in the organs and blood vessels. They recognize information about temperature, oxygen levels, pressure and other parameters and transmit it to the brain for analysis and reaction.

The visceral nervous system consists of two parts, the sympathetic and parasympathetic nervous systems. The sympathetic nervous system is activated in states of stress or danger, causing an increase in heart rate, bronchial dilatation, an increase in blood pressure, and other responses necessary to quickly respond to a threat.

The parasympathetic nervous system, on the other hand, is activated during resting states and allows the body to relax and recover. It reduces heart rate, stimulates digestion, and regulates other functions related to rest and digestion.

CNS sensory and motor functions

The central nervous system (CNS) plays an important role in sensory and motor functions. The sensory functions of the central nervous system are responsible for the perception and processing of information from the external and internal environment.

CNS sensory functions include various types of senses such as vision, hearing, smell, taste and touch. Each of these senses is associated with a specific system of perception in the body and the transmission of signals to the central nervous system.

Motor functions of the CNS are responsible for coordinating and controlling body movements. These functions include planning movements, activating muscles, controlling the strength and speed of movements, and maintaining balance.

The CNS controls motor functions by transmitting signals from nerve cells called motor neurons to the muscles of the body. This process involves coordination between different parts of the CNS, including the brain, spinal cord, and peripheral nervous system.

Sensory and motor functions of the CNS are interrelated processes that ensure the normal functioning of the body. Various diseases and damage to the central nervous system can lead to disruption of these functions and health problems.

Limbic system and emotional processes

The limbic system is a group of structures in the deep parts of the brain that are associated with the processing of emotional and motivational processes. It plays an important role in the formation of emotions, memory, behavior and regulation of instincts.

Hippocampus is a key structure of the limbic system. It is involved in the formation of long-term memory and spatial navigation. Damage to the hippocampus can lead to memory impairment and spatial orientation problems.

Amyndala is another important part of the limbic system that plays a key role in processing and recognizing emotions. It is especially important for the processing of fear reactions and the formation of associations between events and emotions. Damage to the amygdala can lead to changes in emotional behavior and impaired response to threats.

The limbic system also includes the hypothalamus , which regulates emotions and controls the body’s hormonal system. It is involved in the regulation of important processes such as sleep, appetite, sexual behavior and stress responses.

In general, the limbic system plays a fundamental role in emotional processes, memory and behavior. Its functioning is essential for our ability to feel, remember and respond to the world around us.

The role of the CNS in the regulation of sleep and wakefulness

The central nervous system (CNS) plays an important role in the regulation of sleep and wakefulness. It is responsible for controlling the rhythms of day and night, maintaining the sleep-wake cycle, and generating signals that regulate the transition between these states.

One of the key structures of the CNS responsible for sleep and wakefulness is the hypothalamus. It contains special cells called sleep-wake neurons. These neurons act as an internal clockwork and restore our biorhythm, keeping us asleep at night and awake during the day.

In the process of regulating sleep and wakefulness, the CNS interacts with other structures such as the reticular formation, which is responsible for awakening and maintaining wakefulness, and the thalamus, which regulates the transmission of information from sensory organs to the cerebral cortex.

Neurotransmitters, substances that transmit signals between neurons, also play an important role in the regulation of sleep and wakefulness. For example, serotonin is involved in the regulation of mood and sleep, and gamma-aminobutyric acid (GABA) reduces the activity of the nervous system, promoting relaxation and falling asleep.

The overall functioning of the CNS in the regulation of sleep and wakefulness is a complex and interrelated process involving various structures and neurotransmitters. Disruption of these mechanisms can lead to sleep problems such as insomnia or sleepiness at the wrong time.

Brain plasticity and learning

The human brain has an incredible ability to adapt and change its structure and functions under the influence of external and internal factors. This property of the nervous system is called plasticity. It is thanks to the plasticity of the brain that we are able to learn, remember new information and develop our skills.

Learning is one of the strongest stimulations for brain plasticity. In the learning process, our neurons actively interact with each other, creating new connections and strengthening existing ones. However, in order for the brain to be ready for learning, it is necessary to create favorable conditions: a healthy lifestyle, proper nutrition, sufficient sleep and physical activity.

One of the important characteristics of brain plasticity is its ability to regularly update neural connections. The acquisition of new knowledge and skills leads to changes in the structure of the brain, which allows us to adapt to a changing environment.

Scientific studies show that regular training and intellectual activity help to strengthen and improve the cognitive functions of the brain. Studying, reading, learning new languages, solving complex problems – all this trains our brain, making it more flexible and efficient.

It is important to note that brain plasticity persists throughout life. Even adults can change their thought patterns, learn new skills, and improve their memory. That is why it is never too late to start training and developing your brain!

Voice and speech control centers

Voice and speech control centers are located in the brain and play a key role in the production and understanding of speech.

One of the important voice control centers is located in the brain and is called the reticular formation. It plays a role in shaping the voice and controls its basic characteristics such as pitch, intensity and timbre. The reticular formation is also responsible for the regulation of breathing during speech.

Another important speech control center is located in the left hemisphere of the brain and is called the Brock center. It is located in the frontal cortex and is responsible for controlling the motor aspects of speech, such as articulation and coordination of tongue and mouth movements. Damage to this center can lead to broke aphasia, which is characterized by difficulty in pronouncing words and forming grammatically correct phrases.

Another important area related to the control of speech is located in the temporal region of the left hemisphere of the brain and is called the Wernicke center. This center is responsible for understanding and interpreting speech. The defeat of this center can lead to Wernicke’s aphasia, which is characterized by difficulty in understanding and interpreting speech, although the ability to pronounce words remains relatively normal.

Also in the brain there are other centers associated with speech processing, such as centers responsible for recognizing speech sounds, determining and understanding the rhythm and intonation of speech, as well as centers associated with the formation and understanding of semantic information.

The role of the CNS in the process of coordination and balancing

The central nervous system (CNS) plays an important role in coordinating and balancing body movements. It is the main control organ for all bodily functions, including motor skills and balance.

The CNS consists of the brain and spinal cord, which communicate with the rest of the body through nerve impulses. Much of the responsibility for motor coordination lies with the back of the brain, including the cerebellum and its nuclei. The cerebellum performs complex functions in the process of controlling and coordinating the movements of the whole body.

The CNS also plays an important role in maintaining balance and balance in the body. Involved in this process are such CNS structures as inner ear neurons and proprioceptors in muscles and joints. They transmit information about the position of the body and changes in the environment, which allows the CNS to respond and control the balance of the body.

In case of disorders in the CNS, such as injuries, infections or degenerative diseases, coordination and balance problems arise. People with these disorders may have difficulty with accurate and coordinated movement, as well as loss of balance when walking or standing.

Research on the functions of the CNS and its influence on coordination and balance helps develop rehabilitation methods and solve problems associated with motor and balance disorders. Understanding the role of the CNS in these processes allows the development of more effective methods of treatment and rehabilitation for people suffering from these problems.

Effects of the CNS on the Endocrine System

The Central Nervous System (CNS) plays a critical role in regulating the body’s endocrine system. The endocrine system, in turn, includes hormonal organs and produces hormones that regulate various bodily functions.

The CNS controls and regulates the endocrine system by transmitting information through neuroendocrine signals. The key structure in this process is the hypothalamus, which produces and releases founding hormones into the pituitary gland. The pituitary gland, in turn, produces and releases hormones that control the functioning of the endocrine glands.

Nerve impulses transmitted via neuroendocrine signals regulate the production and release of founder hormones and also control the rate of secretion of endocrine hormones. This allows the CNS to control functions such as growth, reproduction, metabolism, stress response, and others.

Possible pathologies and diseases of the central nervous system

The central nervous system (CNS) is subject to various pathological conditions that can seriously impair its functions and lead to health problems. Here are some of the most common CNS diseases:

• Stroke : is a condition resulting from an interrupted blood supply to the brain, resulting in tissue necrosis. A stroke can be caused by embolism or thrombosis of cerebral vessels.
• Epilepsy : is a chronic neurological disease characterized by recurrent and unpredictable seizures caused by temporary disturbances in the electrical activity of the brain.
• Alzheimer’s disease : is a neurodegenerative disease that progresses with age and leads to memory loss, changes in thinking and behavior.
• Parkinsonism : is a chronic neurological disease characterized by incoordination, trembling and slowness of muscle movements.
• Myasthenia gravis : is a rare autoimmune disorder in which antibodies attack neuromuscular junctions and cause muscle weakness and fatigue.

These are just a few examples of CNS pathologies, and there are many other diseases that can affect the normal functioning of the nervous system. Early detection and treatment of these diseases is an important aspect for maintaining health and preventing possible complications.

Q&A:

What is the structure of the central nervous system?

The central nervous system consists of the brain and spinal cord, as well as the spinal and brain nerves.

What are the functions of the central nervous system?

The central nervous system performs a number of important functions, including the transmission of signals between organs and tissues, the control of movements, the regulation of internal organs, and the processing of information.

What are the structures of the brain?

The brain includes such structures as the brain stem, diencephalon, deep brain structures (thalamus, hypothalamus) and cerebral cortex.

How does the central nervous system regulate body movements?

The central nervous system regulates body movements through special signals that are transmitted from the brain to the muscles. The brain generates commands for movements, which are then transmitted through the spinal cord to the appropriate muscles.

What is the nervous system – its functions, structure and facts

The nervous system is a complex network of cells and tissues that transmits messages between the brain and the rest of the body. The nervous system controls every action of the body, from breathing and heartbeat to movement, thoughts and emotions.

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The nervous system consists of two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord. The PNS includes all the nerves that branch from the spinal cord to other parts of the body.

Peripheral Nervous System

Peripheral Nervous System The peripheral nervous system transmits messages between the central nervous system and other parts of the body. The PNS is divided into the somatic and autonomic nervous systems.

The peripheral nervous system consists of the following systems:

Somatic nervous system

The somatic nervous system (SNS) controls the body’s voluntary functions, muscle movement, and sensory organs. Examples are walking, touch and sight.

Autonomic Nervous System

The autonomic nervous system (ANS) controls the involuntary activities of the body, such as heart rate and digestion. The ANS can be divided into the sympathetic nervous system and the parasympathetic nervous system.

Sympathetic nervous system

The sympathetic nervous system (SNS) is responsible for the fight or flight response. It is the body’s emergency response system that prepares us to either fight or flee when we are in danger. The SNS increases heart rate, blood pressure and respiration. It also diverts blood from the digestive system to the muscles so they can be used for physical activity.

Parasympathetic nervous system

The parasympathetic nervous system (PNS) is responsible for the rest-digestion response. This is a normal, relaxed state of the body in which heart rate and blood pressure are lowered and the digestive system is active. The parasympathetic nervous system slows down the heart rate and increases blood flow to the digestive system.

There is a third component of the autonomic nervous system called the enteric nervous system (ENS). ENS acts independently and controls the functions of digestion, but the sympathetic and parasympathetic divisions are carried out.

Central Nervous System (CNS)

Central Nervous System The central nervous system consists of the brain and spinal cord and is responsible for processing and responding to information from the peripheral nervous system.

Brain

The brain is the control center for all activities of the body. It receives information from the senses and sends signals to the rest of the body. The cerebrum, cerebellum and brainstem are the three important parts of the brain.

Cerebrum

The brain is the largest part of the brain and is responsible for our higher level functions such as thinking, reasoning and planning. It is also responsible for our sense organs such as sight, hearing and touch. The brain is divided into two halves called hemispheres. Each hemisphere controls the opposite side of the body.

Cerebellum

The cerebellum is located under the brain at the base of the skull. Its main duty is to coordinate our movements, helping us to keep our balance, walk and stand upright.

Brain stem

The brain stem is the part of the brain that connects the cerebrum and cerebellum to the spinal cord. It controls many automatic functions such as breathing, heart rate and blood pressure.

Spinal Cord

The spinal cord is a long, thin bundle of nerve fibers that runs from the brainstem down the center of the back. The vertebral column, or spine, surrounds it. The spinal cord relays messages between the brain and the rest of the body. It also controls some reflexes, such as the knee jerk.

Nerves

Nerves are the arteries of the nervous system. They carry messages back and forth between the brain and spinal cord and the rest of the body. Nerves are made up of nerve fibers, which are long, thin threads that extend from nerve cells. There are two types of nerve fibers: axons and dendrites.

Nerve cell, or neuron

Nerve cells, or neurons, are the basic units of the nervous system. They are responsible for receiving and transmitting messages. Each neuron has a cell body containing a nucleus. A membrane, called the cell membrane, surrounds the nucleus. The cell body also contains other organelles such as mitochondria and lysosomes.

Axons

Axons are long, thin fibers extending from the cell body. Axons carry messages from the cell body to other neurons, muscles, or glands. They are usually covered in a white fatty substance called myelin. Myelin helps protect the axon and increases the speed of messages.

Dendrites

Dendrites are short, thin fibers that carry messages that extend from the cell body. They receive messages from other neurons and relay them to the cell body. They are usually shorter and thinner than axons.

The synapse is the space between the axon of one neuron and the dendrites of another. Messages are transmitted across the synapse from one neuron to another using electrical impulses and chemical neurotransmitters.

Types of neurons

There are three types of neurons: motor, sensory and interneurons. Some neurons perform both motor and sensory functions.

Sensory neurons

Sensory neurons are responsible for transmitting messages from the sense organs to the brain. They are also known as afferent neurons. Many sensory neurons include touch, temperature, and pain receptors.

Motor neurons

Motor neurons are responsible for transmitting messages from the brain to the muscles. They are also known as efferent neurons. There are both somatic and autonomic motor neurons.

Interneurons

Interneurons are neurons located in the brain and spinal cord. They are responsible for passing messages between other neurons. They also participate in reflexes, passing information directly from sensory neurons to motor neurons, bypassing the brain.

Nerve damage

Nerve damage can result from injury, illness, or exposure to certain toxins. Symptoms of nerve damage are called neuropathy and include numbness, tingling, and pain. Nerve damage can be treated with medication, surgery, or physical therapy. Other options such as flossing, yoga, and acupuncture may also be helpful.

Nerve filament, also called neurodynamic modulation, is a way to treat neuropathy by relieving tension from damaged nerves. The axis of the nerve and the surrounding joints are stretched and stretched, essentially disconnecting the nerve from the surrounding soft tissue.

• Neuropathy around the hip and pelvis often occurs in hemophilia due to a buildup of blood putting pressure on the femoral nerve. A study in teenage boys with hemophilia found that 12 weeks of nerve cord training significantly improved femoral nerve signaling and reduced pain compared to conventional physical therapy.

• Another study showed that four weeks of nerve cord training significantly reduced spasticity (abnormal stiffness) in the wrist and fingers and improved upper limb function in tetraplegic patients after traumatic spinal cord injury.

Peripheral neuropathy is a common side effect of chemotherapy. The results of using yoga to reduce chemotherapy-induced neuropathy have been studied in human survivors of breast, ovarian, and endometrial cancer. The study found that practicing yoga for 60 minutes a day for eight weeks significantly reduced neuropathic pain compared to a non-yoga control group.

Acupuncture can also significantly reduce sensory symptoms and pain and improve the quality of life of patients with chemotherapy-induced neuropathy.

Nervous system disorders

Many different disorders can affect the nervous system. Some of these disorders are temporary and may be caused by stress or lack of sleep. Other diseases, such as Alzheimer’s and Parkinson’s, are permanent and progressive. Treatment for nervous system disorders often includes medication, therapy, and lifestyle changes.

Alzheimer’s disease

Alzheimer’s disease is a degenerative disease that affects the brain. The most common cause of dementia is cognitive decline. Symptoms of Alzheimer’s disease include memory loss, confusion, difficulty with language and motor skills. The disease progresses slowly and can eventually lead to death. There is no cure for Alzheimer’s disease, but there are treatments to help manage the symptoms.

Parkinson’s disease

Parkinson’s disease is a degenerative disease that affects the brain. It is the second most common cause of dementia. Symptoms of Parkinson’s disease include tremors, rigidity, slow movements, and difficulty with balance. The disease progresses slowly and can eventually lead to death. There is no cure for Parkinson’s disease, but there are treatments to help manage the symptoms.

Multiple sclerosis

Multiple sclerosis is a degenerative disease that affects the brain and spinal cord. It is characterized by the presence of areas of damage, called lesions, in the myelin sheath. The myelin sheath is a fatty substance that surrounds and protects nerve fibers. When the myelin sheath becomes damaged, nerve impulses are disrupted and symptoms can occur. Symptoms of multiple sclerosis include fatigue, weakness, muscle spasms, and difficulty with balance. The disease can be mild or severe, and multiple sclerosis cannot be cured. However, there are treatments available to help manage the symptoms.

Cerebral palsy

Cerebral palsy is a disorder that affects movement and muscle tone.