A nerve is a bundle of conductory ?bres called axons (see AXON) that emanate from neurones (see NEURON(E)) – the basic anatomical and functional units of the NERVOUS SYSTEM. Nerves make up the central nervous system (BRAIN and SPINAL CORD) and connect that system to all parts of the body, transmitting information from sensory organs via the peripheral nerves to the centre and returning instructions for action to the relevant muscles and glands.
Nerves vary in size from the large pencil-sized sciatic nerve in the back of the thigh muscles to the single, hair-sized ?bres distributed to the skin. A nerve, such as the sciatic, possesses a strong, outer ?brous sheath, called the epineurium, within which lie bundles of nerve-?bres, divided from one another by partitions of ?brous tissue, in which run blood vessels that nourish the nerve. Each of these bundles is surrounded by its own sheath, known as the perineurium, and within the bundle ?ne partitions of ?brous tissue, known as endoneurium, divide up the bundle into groups of ?bres. The ?nest subdivisions of the nerves are the ?bres, and these are of two kinds: medullated and non-medullated ?bres. (See NEURON(E) and NERVOUS SYSTEM for more details on structure and functions of neurons and nerves.)... nerve
Health Encyclopedia