Nerve

A nerve is an enclosed, cable-like bundle of nerve fibers or axons, which includes the glia that ensheath the axons in myelin. Neurons are sometimes called nerve cells, though this term is technically imprecise since many neurons do not form nerves.

Nerves are part of the peripheral nervous system. Afferent nerves convey sensory signals to the central nervous system, for example from skin or organs, while efferent nerves conduct stimulatory signals from the central nervous system to the muscles and glands. Afferent and efferent fibers are often arranged together, forming mixed nerves.

These signals, sometimes called nerve impulses, are also known as action potentials: 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 neuron through a gap called the synapse.

Clinical importance
Damage to nerves can be caused by physical injury, swelling (e.g. carpal tunnel syndrome), autoimmune diseases (e.g. Guillain-Barré syndrome), diabetes, 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 phenonmenon 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.