The Human Body

Spinal Cord

Spinal Cord, that part of the central nervous axis contained within the vertebral or neural canal. In the adult human it extends from the base of the skull to the second lumbar vertebra. Below this it tapers off as a narrow thread containing little nervous matter. Above the foramen magnum, in the base of the skull, it is continuous with the medulla oblongata. The cord, like the brain, is encased in a triple sheath of membranes and is partially divided into two lateral halves by a median fissure toward the front and a median partition toward the rear; 31 pairs of spinal nerves arise, each by an anterior and a posterior root, from each side of the cord.

The spinal cord functions in the transmission of ascending impulses to the brain and of descending impulses from the brain to the cord. Thus, it conveys to higher centers information brought to it by peripheral nerves from many parts of the body; in addition, it is acted on by impulses from the brain itself. The spinal cord relays impulses also to the muscles, blood vessels, and glands by means of outgoing nerves, either in response to incoming stimuli or to signals from higher levels. See Nervous System; Spinal Column.