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Nerve

A nerve is an enclosed, cable-like bundle of nerve fibers or axons, which includes the glia Glial cell

Glial cells, commonly called neuroglia or simply glia, are non-neuron [i]al cells that provi ... 

 that ensheath the axons in myelin Myelin

Myelin is an electrically insulating phospholipid [i] layer that surrounds the axon [i]s of many neuron [i]s. ... 

. Neuron Neuron

Neurons are a major class of cells [i] in the nervous system [i]. ... 

s are sometimes called nerve cells, though this term is technically imprecise since many neurons do not form nerves. Motor neurons, or nerves innervate or activate muscles groups to perform work.

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Encyclopedia


"Nerves" redirects here. For the online magazine, see Nerve Nerve

[i]s, which includes the [[glia]... 

. For the musical group, see The Nerves The Nerves

The Nerves were a late-'70s power pop [i] trio from Los Angeles [i], California [i], featuring guitarist ... 

. For other uses, see Nerve Nerve

[i]s, which includes the [[glia]... 

.



A nerve is an enclosed, cable-like bundle of nerve fibers or axons, which includes the glia Glial cell

Glial cells, commonly called neuroglia or simply glia, are non-neuron [i]al cells that provi ... 

 that ensheath the axons in myelin Myelin

Myelin is an electrically insulating phospholipid [i] layer that surrounds the axon [i]s of many neuron [i]s. ... 

. Neuron Neuron

Neurons are a major class of cells [i] in the nervous system [i]. ... 

s are sometimes called nerve cells, though this term is technically imprecise since many neurons do not form nerves. Motor neurons, or nerves innervate or activate muscles groups to perform work.

Anatomy

Nerves are part of the peripheral nervous system. Afferent nerve Afferent nerve

In the nervous system [i], afferent neurons--otherwise known as sensory [i] or receptor neuron [i] ... 

s convey sensory signals to the central nervous system Central nervous system

The central nervous system represents the largest part of the nervous system [i], including the brain a ... 

, for example from skin or organs, while efferent nerve Efferent nerve

In the nervous system [i], efferent nerves--otherwise known as motor [i] or effector neuron [i] ... 

s conduct stimulatory signals from the central nervous system to the muscle Muscle

Muscle is contractile [i] tissue [i] of the body and is derived from the mesodermal layer [i] ... 

s and glands. Afferent and efferent fibers are often arranged together, forming mixed nerves.

Most nerves connect to the central nervous system Central nervous system

The central nervous system represents the largest part of the nervous system [i], including the brain a ... 

 through the spinal cord Spinal cord

In vertebrates, the spinal cord is the part of the central nervous system [i] that is enclosed in and pr ... 

. The twelve cranial nerves Cranial nerves

Cranial nerves are nerve [i]s that emerge from the brainstem [i] instead of the spinal cord [i]. ... 

, however, connect directly to parts of the brain Brain

In animal [i]s, the brain, or encephalon , is the control center of the central nervous system [i]. ... 

. Spinal nerve Spinal nerve

The term spinal nerve generally refers to the mixed spinal nerve [i], which is formed from the dorsal an ... 

s are given letter-number combinations according to the vertebra Vertebra

Vertebrae are the individual irregular bones [i] that make up the vertebral column [i] — a flexuou ... 

 through which they connect to the spinal column. Cranial nerves are assigned numbers, usually expressed as Roman numeral Roman numerals

The system of Roman numerals is a numeral system [i] originating in ancient Rome [i], and was adapted fr ... 

s from I to XII. In addition, most nerves and major branches of nerves have descriptive names. Inside the central nervous system, bundles of axons are termed tracts rather than nerves.

The signals nerves carry, sometimes called nerve impulses, are also known as action potential Action potential

An action potential is a wave of electrical [i] discharge that travels along the membrane of a cell [i]... 

s: rapidly traveling electrical waves, which begin typically in the cell body of a neuron and propagate rapidly down the axon to its tip or "terminus." The signals cross over from the terminus to the adjacent neurotransmitter receptor through a gap called the synapse Chemical synapse

Chemical synapses are specialized junctions through which cells of the nervous system [i] signal to one ... 

.

Clinical importance


Damage to nerves can be caused by physical injury, swelling , autoimmune diseases , infection , diabetes Diabetes mellitus

Diabetes mellitus is a disease [i] characterized by persistent hyperglycemia [i] . ... 

, or failure of the blood vessels surrounding the nerve. Pinched nerves occur when pressure is placed on a nerve, usually from swelling due to an injury or pregnancy. Nerve damage or pinched nerves are usually accompanied by pain, numbness, weakness, or paralysis. Patients may feel these symptoms in areas far from the actual site of damage, a phenomenon called referred pain. Referred pain occurs because when a nerve is damaged, signalling is defective from all parts of the area which the nerve receives input, not just the site of the damage.

Neurologists usually first diagnose disorders of the nerves by a physical examination, including the testing of reflexes, walking Walking

Walking is the main form of animal [i] locomotion [i] on land [i], distinguished from running [i] ... 

, muscle Muscle

Muscle is contractile [i] tissue [i] of the body and is derived from the mesodermal layer [i] ... 

 weakness, directed movement, proprioception, and the sense of touch. During the exam, the doctor asks questions about the patients' symptoms and medical history. The initial exam can be followed with tests such as nerve conduction study and electromyography .

See also

  • Nervous system