Spinal Nerve

Thirty-one paired spinal nerves arise from the spinal cord. They are grouped according to the spinal region from which they emerge. There are eight cervical pairs, twelve thoracic pairs, five lumbar, five sacral and one coccygeal pair. Each spinal nerve consists of motor and sensory fibers. A dorsal and ventral spinal nerve root forms each nerve, which emerge from the spinal cord through openings (foramen) in the vertebral column at each of the intervertebral disc spaces. The ventral nerve root fibers are motor fibers while the dorsal root fibers deal with sensation. When the nerve roots merge they form mixed spinal nerves with both motor and sensory innervations. After the nerves pass through the intervertebral foramina they divide into four main branches called Rami. The rami then go to form plexuses by joining with rami from other spinal nerves. Plexus means "braid" which is what the network of nerves resemble. From the plexuses arise the peripheral nerves, which innervate the extremities. These peripheral nerves are named after the body region they innervate or the course they take. The principle plexuses formed by the spinal nerves are the cervical plexus, brachial plexus, lumbar plexus and sacral plexus