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A nerve is an enclosed, cable-like bundle of nerve fibers (called
axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action p ...
s) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the electrochemical nerve impulses called
action potential An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...
s that are transmitted along each of the
axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action p ...
s to peripheral organs or, in the case of sensory nerves, from the periphery back to the
central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...
. Each axon, within the nerve, is an extension of an individual neuron, along with other supportive cells such as some
Schwann cell Schwann cells or neurolemmocytes (named after German physiologist Theodor Schwann) are the principal glia of the peripheral nervous system (PNS). Glial cells function to support neurons and in the PNS, also include satellite cells, olfactory en ...
s that coat the axons in myelin. Within a nerve, each axon is surrounded by a layer of connective tissue called the
endoneurium The endoneurium (also called endoneurial channel, endoneurial sheath, endoneurial tube, or Henle's sheath) is a layer of delicate connective tissue around the myelin sheath of each myelinated nerve fiber in the peripheral nervous system. Its co ...
. The axons are bundled together into groups called fascicles, and each fascicle is wrapped in a layer of connective tissue called the
perineurium The perineurium is a protective sheath that surrounds a nerve fascicle. This bundles together axons targeting the same anatomical location. The perineurium is composed from fibroblasts. In the peripheral nervous system, the myelin sheath of e ...
. Finally, the entire nerve is wrapped in a layer of connective tissue called the epineurium. Nerve cells (often called neurons) are further classified as sensory, motor, or
mixed nerve A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the ...
s. In the
central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...
, the analogous structures are known as
nerve tract A nerve tract is a bundle of nerve fibers (axons) connecting nuclei of the central nervous system. In the peripheral nervous system this is known as a nerve, and has associated connective tissue. The main nerve tracts in the central nervous syst ...
s.


Structure

Each nerve is covered on the outside by a dense sheath of connective tissue, the epineurium. Beneath this is a layer of fat cells, the
perineurium The perineurium is a protective sheath that surrounds a nerve fascicle. This bundles together axons targeting the same anatomical location. The perineurium is composed from fibroblasts. In the peripheral nervous system, the myelin sheath of e ...
, which forms a complete sleeve around a bundle of axons. Perineurial septae extend into the nerve and subdivide it into several bundles of fibres. Surrounding each such fibre is the
endoneurium The endoneurium (also called endoneurial channel, endoneurial sheath, endoneurial tube, or Henle's sheath) is a layer of delicate connective tissue around the myelin sheath of each myelinated nerve fiber in the peripheral nervous system. Its co ...
. This forms an unbroken tube from the surface of the spinal cord to the level where the axon synapses with its muscle fibres, or ends in
sensory receptor Sensory neurons, also known as afferent neurons, are neurons in the nervous system, that convert a specific type of stimulus, via their receptors, into action potentials or graded potentials. This process is called sensory transduction. The cel ...
s. The endoneurium consists of an inner sleeve of material called the glycocalyx and an outer, delicate, meshwork of collagen fibres. Nerves are bundled and often travel along with
blood vessels The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away f ...
, since the neurons of a nerve have fairly high energy requirements. Within the endoneurium, the individual nerve fibres are surrounded by a low-protein liquid called endoneurial fluid. This acts in a similar way to the
cerebrospinal fluid Cerebrospinal fluid (CSF) is a clear, colorless body fluid found within the tissue that surrounds the brain and spinal cord of all vertebrates. CSF is produced by specialised ependymal cells in the choroid plexus of the ventricles of the b ...
in the
central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...
and constitutes a blood-nerve barrier similar to the
blood–brain barrier The blood–brain barrier (BBB) is a highly selective semipermeable border of endothelial cells that prevents solutes in the circulating blood from ''non-selectively'' crossing into the extracellular fluid of the central nervous system where neu ...
. Molecules are thereby prevented from crossing the blood into the endoneurial fluid. During the development of nerve edema from nerve irritation (or injury), the amount of endoneurial fluid may increase at the site of irritation. This increase in fluid can be visualized using magnetic resonance neurography, and thus MR neurography can identify nerve irritation and/or injury.


Categories

Nerves are categorized into three groups based on the direction that signals are conducted: *
Afferent nerve A sensory nerve, or afferent nerve, is a general anatomic term for a nerve which contains predominantly somatic afferent nerve fibers. Afferent nerve fibers in a sensory nerve carry sensory information toward the central nervous system (CNS) fro ...
s conduct signals from
sensory neuron Sensory neurons, also known as afferent neurons, are neurons in the nervous system, that convert a specific type of stimulus, via their receptors, into action potentials or graded potentials. This process is called sensory transduction. The ...
s to the
central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...
, for example from the
mechanoreceptors A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanoreceptors are innervated by sensory neurons that convert mechanical pressure into electrical signals that, in animals, ...
in skin. *
Efferent nerve Efferent nerve fibers refer to axonal projections that ''exit'' a particular region; as opposed to afferent projections that ''arrive'' at the region. These terms have a slightly different meaning in the context of the peripheral nervous syste ...
s conduct signals from the central nervous system along motor neurons to their target muscles and
gland In animals, a gland is a group of cells in an animal's body that synthesizes substances (such as hormones) for release into the bloodstream ( endocrine gland) or into cavities inside the body or its outer surface ( exocrine gland). Structure ...
s. *
Mixed nerve A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the ...
s contain both afferent and efferent axons, and thus conduct both incoming sensory information and outgoing muscle commands in the same bundle. All spinal nerves are mixed nerves, and some of the cranial nerves are also mixed nerves. Nerves can be categorized into two groups based on where they connect to the central nervous system: *
Spinal nerve A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the ...
s innervate (distribute to/stimulate) much of the body, and connect through the vertebral column to the spinal cord and thus to the
central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...
. They are given letter-number designations according to the
vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
through which they connect to the spinal column. *
Cranial nerves Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and f ...
innervate parts of the head, and connect directly to the brain (especially to the
brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is conti ...
). They are typically assigned Roman numerals from 1 to 12, although cranial nerve zero is sometimes included. In addition, cranial nerves have descriptive names.


Terminology

Specific terms are used to describe nerves and their actions. A nerve that supplies information to the brain from an area of the body, or controls an action of the body is said to "innervate" that section of the body or organ. Other terms relate to whether the nerve affects the same side ("ipsilateral") or opposite side ("contralateral") of the body, to the part of the brain that supplies it.


Development

Nerve growth normally ends in adolescence, but can be re-stimulated with a molecular mechanism known as "
Notch signaling The Notch signaling pathway is a highly conserved cell signaling system present in most animals. Mammals possess four different notch receptors, referred to as NOTCH1, NOTCH2, NOTCH3, and NOTCH4. The notch receptor is a single-pass transmem ...
".


Regeneration

If the axons of a neuron are damaged, as long as the cell body of the neuron is not damaged, the axons can regenerate and remake the synaptic connections with neurons with the help of
guidepost cells Guidepost cells are cells which assist in the subcellular organization of both neural axon growth and migration. They act as intermediate targets for long and complex axonal growths by creating short and easy pathways, leading axon growth cones tow ...
. This is also referred to as
neuroregeneration Neuroregeneration refers to the regrowth or repair of nervous tissues, cells or cell products. Such mechanisms may include generation of new neurons, glia, axons, myelin, or synapses. Neuroregeneration differs between the peripheral nervous syst ...
. The nerve begins the process by destroying the nerve
distal Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
to the site of injury allowing Schwann cells, basal lamina, and the neurilemma near the injury to begin producing a regeneration tube. Nerve growth factors are produced causing many nerve sprouts to bud. When one of the growth processes finds the regeneration tube, it begins to grow rapidly towards its original destination guided the entire time by the regeneration tube. Nerve regeneration is very slow and can take up to several months to complete. While this process does repair some nerves, there will still be some functional deficit as the repairs are not perfect.


Function

A nerve conveys information in the form of electrochemical impulses (as nerve impulses known as
action potential An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...
s) carried by the individual neurons that make up the nerve. These impulses are extremely fast, with some myelinated neurons conducting at speeds up to 120 m/s. The impulses travel from one neuron to another by crossing a synapse, where the message is converted from
electrical Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described ...
to chemical and then back to electrical. Nerves can be categorized into two groups based on function: * An
afferent nerve fiber Afferent nerve fibers are the axons (nerve fibers) carried by a sensory nerve that relay sensory information from sensory receptors to regions of the brain. Afferent projections ''arrive'' at a particular brain region. Efferent nerve fibers a ...
conducts sensory information from a
sensory neuron Sensory neurons, also known as afferent neurons, are neurons in the nervous system, that convert a specific type of stimulus, via their receptors, into action potentials or graded potentials. This process is called sensory transduction. The ...
to the central nervous system, where the information is then processed. Bundles of fibres or
axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action p ...
s, in the peripheral nervous system are called nerves, and bundles of afferent fibers are known as ''sensory nerves''. * An efferent nerve fiber conducts signals from a motor neuron in the central nervous system to muscles. Bundles of these fibres are known as ''efferent nerves''.


Nervous system

The nervous system is the part of an
animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...
that coordinates its actions by transmitting
signals In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The ''IEEE Transactions on Signal Processing'' ...
to and from different parts of its body. In vertebrates it consists of two main parts, the
central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...
(CNS) and the peripheral nervous system (PNS). The CNS consists of the brain,
brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is conti ...
and spinal cord. The PNS consists mainly of nerves, which are enclosed bundles of the long fibers or
axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action p ...
s, that connect the CNS to all remaining body parts. Nerves that transmit signals from the CNS are called '' motor'' or '' efferent'' nerves, while those nerves that transmit information from the body to the CNS are called ''sensory'' or ''afferent''.
Spinal nerve A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the ...
s serve both functions and are called ''mixed'' nerves. The PNS is divided into three separate subsystems, the
somatic Somatic may refer to: * Somatic (biology), referring to the cells of the body in contrast to the germ line cells ** Somatic cell, a non-gametic cell in a multicellular organism * Somatic nervous system, the portion of the vertebrate nervous syst ...
, autonomic, and
enteric The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...
nervous systems. Somatic nerves mediate voluntary movement. The autonomic nervous system is further subdivided into the sympathetic and the parasympathetic nervous systems. The sympathetic nervous system is activated in cases of emergencies to mobilize energy, while the parasympathetic nervous system is activated when organisms are in a relaxed state. The enteric nervous system functions to control the gastrointestinal system. Both autonomic and enteric nervous systems function involuntarily. Nerves that exit from the cranium are called
cranial nerves Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and f ...
while those exiting from the spinal cord are called spinal nerves.


Clinical significance

Cancer can spread by invading the spaces around nerves. This is particularly common in head and neck cancer, prostate cancer and
colorectal cancer Colorectal cancer (CRC), also known as bowel cancer, colon cancer, or rectal cancer, is the development of cancer from the colon or rectum (parts of the large intestine). Signs and symptoms may include blood in the stool, a change in bowel m ...
. Nerves can be damaged by physical injury as well as conditions like carpal tunnel syndrome and repetitive strain injury.
Autoimmune disease An autoimmune disease is a condition arising from an abnormal immune response to a functioning body part. At least 80 types of autoimmune diseases have been identified, with some evidence suggesting that there may be more than 100 types. Nearly a ...
s such as Guillain–Barré syndrome,
neurodegenerative disease A neurodegenerative disease is caused by the progressive loss of structure or function of neurons, in the process known as neurodegeneration. Such neuronal damage may ultimately involve cell death. Neurodegenerative diseases include amyotrophic ...
s,
polyneuropathy Polyneuropathy ( poly- + neuro- + -pathy) is damage or disease affecting peripheral nerves (peripheral neuropathy) in roughly the same areas on both sides of the body, featuring weakness, numbness, and burning pain. It usually begins in the hand ...
, infection,
neuritis Neuritis () is inflammation of a nerve or the general inflammation of the peripheral nervous system. Inflammation, and frequently concomitant demyelination, cause impaired transmission of neural signals and leads to aberrant nerve function. Neu ...
, diabetes, or failure of the blood vessels surrounding the nerve all cause
nerve damage Nerve injury is an injury to nervous tissue. There is no single classification system that can describe all the many variations of nerve injuries. In 1941, Seddon introduced a classification of nerve injuries based on three main types of nerve ...
, which can vary in severity. Multiple sclerosis is a disease associated with extensive nerve damage. It occurs when the macrophages of an individual's own immune system damage the myelin sheaths that insulate the axon of the nerve. A pinched nerve occurs when pressure is placed on a nerve, usually from swelling due to an injury, or pregnancy and can result in pain, weakness, numbness or paralysis, an example being carpal tunnel syndrome. Symptoms can be felt in areas far from the actual site of damage, a phenomenon called referred pain. Referred pain can happen when the damage causes altered signalling to other areas.
Neurologists Neurology (from el, νεῦρον (neûron), "string, nerve" and the suffix -logia, "study of") is the branch of medicine dealing with the diagnosis and treatment of all categories of conditions and disease involving the brain, the spinal ...
usually diagnose disorders of nerves by a physical examination, including the testing of
reflex In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus. Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...
es, walking and other directed movements,
muscle weakness Muscle weakness is a lack of muscle strength. Its causes are many and can be divided into conditions that have either true or perceived muscle weakness. True muscle weakness is a primary symptom of a variety of skeletal muscle diseases, includi ...
, proprioception, and the sense of
touch In physiology, the somatosensory system is the network of neural structures in the brain and body that produce the perception of touch (haptic perception), as well as temperature (thermoception), body position (proprioception), and pain. It is ...
. This initial exam can be followed with tests such as nerve conduction study, electromyography (EMG), and computed tomography (CT).


Other animals

A neuron is called ''identified'' if it has properties that distinguish it from every other neuron in the same animal—properties such as location, neurotransmitter, gene expression pattern, and connectivity—and if every individual organism belonging to the same species has exactly one neuron with the same set of properties. In vertebrate nervous systems, very few neurons are "identified" in this sense. Researchers believe humans have none—but in simpler nervous systems, some or all neurons may be thus unique. In vertebrates, the best known identified neurons are the gigantic
Mauthner cell The Mauthner cells are a pair of big and easily identifiable neurons (one for each half of the body) located in the rhombomere 4 of the hindbrain in fish and amphibians that are responsible for a very fast escape reflex (in the majority of animals ...
s of fish. Every fish has two Mauthner cells, located in the bottom part of the brainstem, one on the left side and one on the right. Each Mauthner cell has an axon that crosses over, innervating (stimulating) neurons at the same brain level and then travelling down through the spinal cord, making numerous connections as it goes. The synapses generated by a Mauthner cell are so powerful that a single action potential gives rise to a major behavioral response: within milliseconds the fish curves its body into a C-shape, then straightens, thereby propelling itself rapidly forward. Functionally this is a fast escape response, triggered most easily by a strong sound wave or pressure wave impinging on the lateral line organ of the fish. Mauthner cells are not the only identified neurons in fish—there are about 20 more types, including pairs of "Mauthner cell analogs" in each spinal segmental nucleus. Although a Mauthner cell is capable of bringing about an escape response all by itself, in the context of ordinary behavior other types of cells usually contribute to shaping the amplitude and direction of the response. Mauthner cells have been described as command neurons. A command neuron is a special type of identified neuron, defined as a neuron that is capable of driving a specific behavior all by itself. Such neurons appear most commonly in the fast escape systems of various species—the squid giant axon and
squid giant synapse The squid giant synapse is a chemical synapse found in squid. It is the largest chemical junction in nature. Anatomy The squid giant synapse (Fig 1) was first recognized by John Zachary Young in 1939. It lies in the stellate ganglion on each side ...
, used for pioneering experiments in neurophysiology because of their enormous size, both participate in the fast escape circuit of the squid. The concept of a command neuron has, however, become controversial, because of studies showing that some neurons that initially appeared to fit the description were really only capable of evoking a response in a limited set of circumstances. In organisms of radial symmetry,
nerve net A nerve net consists of interconnected neurons lacking a brain or any form of cephalization. While organisms with bilateral body symmetry are normally associated with a condensation of neurons or, in more advanced forms, a central nervous syst ...
s serve for the nervous system. There is no brain or centralised head region, and instead there are interconnected neurons spread out in nerve nets. These are found in
Cnidaria Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter. Their distinguishing feature is cnidocytes, specialized cells that th ...
,
Ctenophora Ctenophora (; ctenophore ; ) comprise a phylum of marine invertebrates, commonly known as comb jellies, that inhabit sea waters worldwide. They are notable for the groups of cilia they use for swimming (commonly referred to as "combs"), and ...
and Echinodermata.


History

Herophilos Herophilos (; grc-gre, Ἡρόφιλος; 335–280 BC), sometimes Latinised Herophilus, was a Greek physician regarded as one of the earliest anatomists. Born in Chalcedon, he spent the majority of his life in Alexandria. He was the first sc ...
335–280 BC, described the
optic nerve In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived from ...
and the
oculomotor nerve The oculomotor nerve, also known as the third cranial nerve, cranial nerve III, or simply CN III, is a cranial nerve that enters the orbit through the superior orbital fissure and innervates extraocular muscles that enable most movements of ...
for sight and eye movement. Analysis of the nerves in the cranium allowed him to differentiate between blood vessels and nerves i.e. grc, νεῦρον (neûron), ''“string (plant fiber), nerve”''.


See also

* Connective tissue in the peripheral nervous system * Dermatome (anatomy) *
List of nerves of the human body The following is a list of nerves in the human body: Location * Structure of the nervous system * Development of the nervous system * The spinal cord or medulla spinalis * The brain or encephalon ** The hindbrain or rhombencephalon ** The midb ...
* Nerve injury * Nervous system *
Neuropathy Peripheral neuropathy, often shortened to neuropathy, is a general term describing disease affecting the peripheral nerves, meaning nerves beyond the brain and spinal cord. Damage to peripheral nerves may impair sensation, movement, gland, or or ...
*
Peripheral nerve injury Nerve injury is an injury to nervous tissue. There is no single classification system that can describe all the many variations of nerve injuries. In 1941, Seddon introduced a classification of nerve injuries based on three main types of nerve f ...
* Peripheral nerve injury classification


References


Further reading


Nervous system
William E. Skaggs, Scholarpedia * * * * Squire, L. ''et al.'' (2012). ''Fundamental Neuroscience, 4th edition''.
Academic Press Academic Press (AP) is an academic book publisher founded in 1941. It was acquired by Harcourt, Brace & World in 1969. Reed Elsevier bought Harcourt in 2000, and Academic Press is now an imprint of Elsevier. Academic Press publishes referen ...
; * * Damasio, A. R. (1994). ''Descartes' Error: Emotion, Reason, and the Human Brain. '' New York,
Avon Books Avon Publications is one of the leading publishers of romance fiction. At Avon's initial stages, it was an American paperback book and comic book publisher. The shift in content occurred in the early 1970s with multiple Avon romance titles reach ...
. (Hardcover) (Paperback) * Gardner, H. (1976). ''The Shattered Mind: The Person After Brain Damage. '' New York,
Vintage Books Vintage Books is a trade paperback publishing imprint of Penguin Random House originally established by Alfred A. Knopf in 1954. The company was purchased by Random House in April 1960, and a British division was set up in 1990. After Random Hou ...
, 1976 * Goldstein, K. (2000). ''The Organism. '' New York, Zone Books. (Hardcover) (Paperback) *


External links


List of nerves
* (human) * (non-human) {{Authority control Nerves Peripheral nervous system Neuroanatomy Soft tissue