Author: Jana Vasković•Reviewer: Nicola McLaren MScLast reviewed: September 16, 2021Reading time: 20 minutes

Nervous system (anterior view)

The nervous system is a network that neurons whose main attribute is come generate, modulate and also transmit information between all the various parts of the human body. This property permits many crucial functions of the nervous system, such as regulation of an essential body features (heartbeat, breathing, digestion), sensation and also body movements. Ultimately, the nervous mechanism structures preside over whatever that renders us human; our consciousness, cognition, behaviour and also memories.

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The worried system consists of 2 divisions; 

Key facts around the worried system
DefinitionA network of neurons the sends, receives and also modulates neural impulses in between different human body parts.
DivisionsCentral concerned systemPeripheral nervous system
Central nervous systemBrain and also spinal cord
Peripheral worried systemSpinal and cranial nerves.Functional divisions:- Somatic worried system- Autonomic nervous system; sympathetic, parasympathetic and also enteric divisions

Understanding the nervous mechanism requires knowledge of its assorted parts, therefore in this write-up you will certainly learn about the nervous system break down and all its assorted divisions.

Cells that the worried system Peripheral worried systemAutonomic worried systemClinical notes
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Neurons, or nerve cell, space the key structural and functional devices of the worried system. Every neuron consists of a body (soma) and a number of processes (neurites). The nerve cabinet body includes the moving organelles and also is whereby neural impulses (action potentials) space generated. The procedures stem from the body, they attach neurons with each other and with various other body cells, enabling the circulation of neural impulses. There are two species of neural processes that differ in structure and function; 

Axons are long and also conduct impulses far from the neuronal body. Dendrites room short and also act to receive impulses from other neurons, conducting the electric signal towards the nerve cell body.

Every neuron has actually a solitary axon, when the variety of dendrites varies. Based on that number, there are four structural types of neurons; multipolar, bipolar, pseudounipolar and unipolar. 

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There space two species of neurons, named according to even if it is they send an electric signal towards or far from the CNS;

Afferent neurons (sensory or ascending) conduct impulses from the peripheral organization to the CNS. These impulses save sensory information, describing the tissue"s environment.

The website where one axon connect to one more cell to pass the neural impulse is called a synapse. The synapse doesn"t connect to the following cell directly. Instead, the impulse triggers the relax of chemicals called neurotransmitters from the an extremely end of an axon. These neurotransmitters bind to the effector cell membrane, causing biochemical events to take place within the cell follow to the orders sent out by the CNS.

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Glial cells


Glial cells, additionally called neuroglia or merely glia, are smaller sized non-excitatory cells the act to assistance neurons. They perform not propagate action potentials. Instead, castle myelinate neurons, maintain homeostatic balance, administer structural support, protection and nutrition for neurons throughout the worried system. 

This set of functions is detailed for by four different varieties of glial cells;

Myelinating glia produce the axon-insulating myelin sheath. These are dubbed oligodendrocytes in the CNS and also Schwann cells in the PNS. Mental these easily with the mnemonic "COPS" (Central - Oligodendrocytes; Peripheral - Schwann)Astrocytes (CNS) and satellite glial cells (PNS) both re-superstructure the function of supporting and protecting neurons. 

Most axons space wrapped through a white insulating substance referred to as the myelin sheath, created by oligodendrocytes and Schwann cells. Myelin encloses an axon segmentally, leaving unmyelinated gaps in between the segments referred to as the nodes that Ranvier. The neural impulses propagate v the Ranvier nodes only, omitted the myelin sheath. This considerably increases the rate of neural advertise propagation. 

White and gray matter


The white color of myelinated axons is identified from the gray fancy neuronal bodies and also dendrites. Based upon this, nervous organization is separated into white matter and gray matter, both the which has a certain distribution; 

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Nervous mechanism divisions

Nervous system break down (diagram)

So concerned tissue, comprised of neurons and also neuroglia, creates our nervous offal (e.g. The brain, nerves). This organs unite according to their usual function, forming the evolution perfection that is our nervous system. 

The nervous system (NS) is structurally broken down into two divisions; 

Central nervous mechanism (CNS) - consists of the brain and spinal cordPeripheral nervous mechanism (PNS) - gathers all neural tissue exterior the CNS

Functionally, the PNS is further subdivided right into two sensible divisions; 

Somatic nervous mechanism (SNS) - informally explained as the spontaneous systemAutonomic nervous system (ANS) - defined as the involuntary system. 

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Although split structurally into main and peripheral parts, the worried system departments are actually interconnected through each other. Axon bundles happen impulses in between the brain and spinal cord. This bundles within the CNS are referred to as afferent and also efferent neural pathways or tracts. Axons that prolong from the CNS to attach with peripheral tissues belong to the PNS. Axons bundles within the PNS are dubbed afferent and efferent peripheral nerves.

Central concerned system

The central nervous device (CNS) is composed of the mind and spinal cord. This are found housed in ~ the skull and also vertebral tower respectively.

The brain is made of 4 parts; cerebrum, diencephalon, cerebellum and also brainstem. With each other these parts process the incoming information from peripheral tissues and generate commands; telling the tissues how to respond and function. These commands tackle the most facility voluntary and also involuntary human being body functions, from breathing to thinking.

The spinal cord proceeds from the brainstem. It additionally has the ability to create commands however for involuntary processes only, i.e. Reflexes. However, the main duty is to pass information between the CNS and periphery. 

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The PNS consists the 12 bag of cranial nerves, 31 bag of spinal nerves and also a number of small neuronal swarm throughout the body dubbed ganglia.Peripheral nerves deserve to be sensory (afferent), engine (efferent) or blended (both). Relying on what structures they innervate, peripheral nerves can have the complying with modalities;

General - supplying every little thing except one-of-a-kind senses

Cranial nerves

12 cranial nerves (diagram)

Cranial nerves space peripheral nerves that arise from the cranial nerve nuclei the the brainstem and also spinal cord. Lock innervate the head and neck. Cranial nerves are numbered one come twelve follow to your order of departure through the skull fissures. Namely, castle are: olfactory nerve (CN I), optic nerve (CN II), oculomotor nerve (CN III), trochlear nerve (CN IV), trigeminal nerve (CN V), abducens nerve (VI), facial nerve (VII), vestibulocochlear nerve (VIII), glossopharyngeal nerve (IX), vagus nerve (X), accessory nerve (XI), and hypoglossal nerve (XII). These nerves room motor (III, IV, VI, XI, and XII), sensory (I, II and also VIII) or blended (V, VII, IX, and X).

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Spinal nerves

Spinal nerves (diagram)

Spinal nervesemerge native the segment of the spinal cord. They are numbered follow to their details segment that origin. Hence, the 31 pairs that spinal nerves are separated into 8 cervical pairs, 12 thoracic pairs, 5 lumbar pairs, 5 sacral pairs, and 1 coccygeal spinal nerve. All spinal nerves space mixed, containing both sensory and also motor fibers.

Spinal nerves innervate the whole body, through the exemption of the head. They perform so by either straight synapsing v their target guts or by interlacing v each other and forming plexuses. There space four major plexuses that supply the human body regions; 

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Ganglia (sing. Ganglion) space clusters the neuronal cabinet bodies exterior of the CNS, definition that they are the PNS equivalents to subcortical nuclei the the CNS. Ganglia can be sensory or visceral motor (autonomic) and their distribution in the body is clearly defined.

Dorsal root ganglia space clusters that sensory nerve cabinet bodies located surrounding to the spinal cord, They room a component of the posterior root of a spinal nerve.

Autonomic ganglia room either sympathetic or parasympathetic. Sympathetic ganglia are found in the thorax and abdomen, grouped right into paravertebral and also prevertebral ganglia. Paravertebral ganglia lie on either next of vertebral pillar (para- method beside), consisting of two ganglionic chains that prolong from the base of the skull come the coccyx, dubbed sympathetic trunks. Prevertebral ganglia (collateral ganglia, preaortic ganglia) are found anterior come the vertebral obelisk (pre- method in prior of), closer to your target organ. Castle are more grouped follow to which branch of abdominal muscle aorta lock surround; celiac, aorticorenal, superior and also inferior mesenteric ganglia.

Parasympathetic ganglia are found in the head and pelvis. Ganglia in the head are connected with pertinent cranial nerves and are the ciliary, pterygopalatine, otic and also submandibular ganglia. Pelvic ganglia lie close to the reproductive organs making up autonomic plexuses for innervation the pelvic viscera, such as prostatic and also uterovaginal plexuses.

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Somatic concerned system

The somatic worried system is the voluntary ingredient of the peripheral nervous system. It consists of all the fibers in ~ cranial and also spinal nerves that enable us to do voluntary body activities (efferent nerves) and also feel emotion from the skin, muscles and joints (afferent nerves). Somatic emotion relates to touch, pressure, vibration, pain, temperature, stretch and position sense from these three types of structures. 

Sensation native the glands, smooth and cardiac muscles is conveyed by the autonomic nerves.

Autonomic concerned system

The autonomic nervous system is the involuntary component of the peripheral concerned system. Further split into the forgiveness (SANS), parasympathetic (PANS) systems, it is consisted of exclusively that visceral engine fibers. Nerves from both these departments innervate all involuntary structures of the body; 

Balanced to work of this two equipment plays a an essential role in preserving homeostasis, definition that the SANS and PANS do not oppose every other but rather, they enhance each other. They execute so through potentiating the task of different organs under assorted circumstances; for example, the PSNS will stimulate greater intestine activity after food intake, while SANS will stimulate the love to boost the output throughout exercise.

Autonomic nerves synapse in ~ autonomic ganglia prior to reaching your target organ, thus all of them have presynaptic and also postsynaptic parts. Presynaptic fibers originate native CNS and also end by synapsing with neurons that the peripheral autonomic ganglia. Postsynaptic fibers room the axons the ganglion neurons, extending from the ganglion to peripheral tissues. In sympathetic nerves, the presynaptic fiber is short as the ganglia room located really close come the spinal cord, if the postsynaptic fiber is much longer in bespeak to reach the target organ. In parasympathetic nerves the the opposite; the presynaptic fiber is much longer than the postsynaptic.

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Sympathetic worried system

The sympathetic system (SANS) adjusts our bodies for situations of raised physical activity. Its actions are typically described together the “fight-or-flight” response as that stimulates responses such as much faster breathing, raised heart rate, elevated blood pressure, dilated pupils and redirection of blood flow from the skin, kidneys, stomach and intestines to the heart and muscles, whereby it’s needed. 

Sympathetic nerve fibers have actually a thoracolumbar origin, definition that lock stem native the T1-L2/L3 spinal cord segments. Lock synapse with prevertebral and also paravertebral ganglia, from which the postsynaptic fibers take trip to it is provided the target viscera.

Parasympathetic nervous system

The parasympathetic nervous system (PSNS) adjusts our bodies for power conservation, activating “rest and digest” or “feed and breed” activities. The nerves the the PSNS slow-moving down the action of cardiovascular system, draw away blood far from muscles and increase peristalsis and gland secretion. 

Parasympathetic fibers have actually craniosacral outflow, an interpretation that castle originate native the brainstem (cranio-) and S2-S4 spinal cord segment (-sacral). This fibers travel to thoracic and abdominal muscle organs, where they synapse in ganglia situated close come or in ~ the target organ.

Enteric concerned system

Enteric nervous system comprises the SANS and PANS yarn that regulate the task of the cradle tract. This system is do of parasympathetic yarn of the vagus nerve (CN X) and sympathetic yarn of the thoracic splanchnic nerves. These fibers type two plexuses within the wall surface of the intestinal tube which room responsible for modulating intestinal peristalsis, i.e. Propagation of spend food from esophagus to rectum;

Submucosal plexus (of Meissner) found in the submucosa of the intestines and contains just parasympathetic fibersMnemonic

You can easily remember these two plexuses making use of a an easy mnemonic! " SMP & MAPS", i m sorry stands for:


Clinical notes


Vagotomy because that gastric ulcers is an old procedure which is offered as surgical monitoring in patients with recurrent gastric ulcers as soon as there is no effect of diet alterations or antiulcer drugs. The vagus nerve stimulates the cheap of gastric acid. Three species of vagotomy can be performed i beg your pardon would greatly diminish this effect.

Cranial nerve palsies

The 12 cranial nerves every leave/enter the skull through assorted foramina. Narrowing of these foramina or any constriction follow me the nerves course results in nerve palsy. Because that example, Bell’s palsy affect the face nerve. On the influenced side that the face, the patience has:

hemiplegiadry eyesan absent corneal reflex, overloud hearing and influenced taste in the anterior 2/3 the the lacking corneal reflexoverloud hearing

affected taste in the anterior 2/3 of the tongue

Limb nerve lesions

Limb nerve palsies often result from fracture, constriction or overuse. Because that example, carpal tunnel syndrome affects the typical nerve, and occurs once the nerve is compressed within the tunnel. This is as result of enlargement the the flexor tendons within the tunnel or swelling because of oedema. It regularly occurs in pregnancy and also acromegaly.

Hirschsprung’s disease

This is colonic atony second to a fail of the ganglion cells (described in the enteric nervous device section) to migrate into the enteric concerned system. This outcomes in a severely constipated and also malnourished child, i m sorry is in desperate need of corrective surgery.

Spina bifida

Failure the normal development of the meninges and/or vertebral neural arch results in a defect commonly in the lumbar spine, where component of the spinal cord is covered just by meninges and therefore sits exterior the body. Both environmental and also genetic factors add to that cause. Folate supplements space now provided to all pregnant mother in beforehand pregnancy for its prevention.

Parkinson’s disease

Dopamine is important for the exactly functioning that the basal ganglia, structures in the brain that manage our cognition and movement. Parkinson’s patient suffer destruction of these dopaminergic neurons in the substantia nigra, result in:

difficulty initiating movementshuffling gaitmasked faciescog-wheel/lead-pipe rigidity in the limbs



Blumenfeld, H. (2018). Neuroanatomy v clinical cases. Sunderland, MA: Sinauer.Goodfellow, J., Collins, D., Silva, D., Dardis, R., & Nagaraya, S. (2016). Neurology & neurosurgery. Brand-new Delhi, India: Jp medical pub.Patestas, M. A., & Gartner, L. P. (2016). A textbook that neuroanatomy. Hoboken: Wiley BlackwellWaxman, S. G. (2010). Clinical neuroanatomy. New York: McGraw-Hill Medical.

Author, review and layout:


Nervous system (anterior view) - Begoña Rodriguez12 cranial nerves (diagram) - Paul Kim

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