spinal nerves, the 31 pairs of nerves without special names that are connected to the spinal cord and numbered according to the level of the vertebral column at which they emerge. There are 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal pair. The first cervical pair of nerves emerges from the spinal cord in the space between the first cervical vertebra and the occipital bone. The rest of the cervical pairs and all the thoracic pairs emerge horizontally through the intervertebral foramina of their respective vertebrae, such as the second cervical pair, which emerges through the foramina above the second cervical vertebra. The lumbar, sacral, and coccygeal nerve pairs descend from their points of origin at the lower end of the cord before reaching the intervertebral foramina of their respective vertebrae. Each spinal nerve attaches to the spinal cord by an anterior (or ventral) root and a posterior (or dorsal) root. The nerve impulses enter the cord by way of posterior roots. The posterior roots supply skin and muscles of much of the body with some of the nerve fibers supplying autonomic functions. The posterior roots contain sensory neurons and accompany a distended spinal ganglion within the vertebral foramina. The ventral roots contain motor neuron axons. The sacral plexus in the pelvic cavity comprises certain spinal nerve fibers from the lumbar and sacral regions and gives rise to the great sciatic nerve in the back of the thigh. See also spinal cord.
