Spinal Nerves
the name applied to the paired nerves which arise from the spinal cord, and which are distributed to the various parts of the body. The spinal nerves are so named in contradistinction to the cranial nerves, or those which originate from the brain itself. Thirty-one pairs of spinal nerves arise from the spinal cord of man. They pass from the spinal cord and spine through the intervertebral foramina, or openings between the bodies of the vertebræ. Eight pairs are cervical; 12 are dorsal nerves, also named thoracic; 5 are lumbar, 5 5 sacral, sao and 1 co coccygeal.
Each spinal nerve arises by two roots, an anterior and posterior, from the spinal column. The posterior root has a nerve mass or ganglion, which is wanting in the anterior. The fibers of the anterior roots are motor in nature, i. e., impulses travel by these roots outward from the cord or brain to the body. The fibers of the posterior roots are sensory, i. e., impulses are conveyed by these fibers to the cord or brain. The anterior and posterior fibers unite just beyond the nervous ganglion to form a single nerve trunk, in which the two sets of fibers are indistinguishable. See NERVE.