Nerve

The common name for neuron, the basic fiber, or bundles of fibers, that transmit information to and from the muscles, glands, organs, spinal cord, and brain.

Nerves form the network of connections that receive signals, known as sensory input, from the environment and within the body and transmit the body's responses, or instructions for action, to the muscles, organs, and glands. The central nervous system, comprised of the brain and spinal cord, sends information throughout the body over the network of nerves known collectively as the peripheral nervous system. The nerves of the peripheral nervous system are in pairs, with one usually leading to the left side and the other to the right side of the body. There are 12 nerve pairs, called cranial nerves, that connect directly to the brain and control such functions as vision and hearing. Thirty-one nerve pairs are connected directly to the spinal cord, branching out to the rest of the body.

The peripheral nervous system may be further subdivided into the autonomic nervous system, which regulates involuntary functions such as breathing, digestion, beating of the heart, and the somatic nervous system, which controls voluntary functions, such as walking, picking up a pencil, and reading this page. The cells of the central nervous system do not have the ability to regenerate, and are not replaced directly if they are damaged.