Nerve

A bundle of nerve fibres which travel to a common location. Nerve fibres, known as axons, are the filamentous projections of many individual neurons (nerve cells). The most obvious nerves in the body are the peripheral nerves, which extend from the central nervous system (consisting of the brain and spinal cord). Of these, 12 pairs of cranial nerves link directly to the brain, and 31 pairs of spinal nerves join the spinal cord. In the shoulder and hip regions, the spinal nerves join to form plexuses, from which branch the main nerves to the limbs. Most nerves divide at numerous points to send branches to all parts of the body, particularly to the sense organs, the skin, skeletal muscles, internal organs, and glands. Nerve fibres may have a sensory function, carrying information from a receptor or sense organ towards the central nervous system (CNS), or they may have a motor function, carrying instructions from the CNS to a muscle or a gland. The messages are carried by electrical impulses propagated along the fibres. Some nerves carry only sensory or motor fibres, but most carry both. Nerve function is sensitive to cold, pressure, and injury (see nerve injury). The peripheral nerves can be damaged by a wide variety of disorders, including infection, inflammation, and metabolic disorders (see neuropathy).