Chapter 4 - The Spinal Nerves

Abstract

This chapter describes the anatomy of the dorsal and ventral roots and spinal nerves. The spinal nerves transmit sensory information from the target organs to the central nervous system, and send motor commands from the central nervous system to muscles and target organs. Along the entire length of the spinal cord, spinal nerves arise at regular intervals and leave the vertebral column between the adjacent vertebrae through the intervertebral foramina. Each spinal nerve is attached to the spinal cord by a ventral (anterior) and a dorsal (posterior) root. The ventral and dorsal roots join together and form the spinal nerve at each segmental level. The spinal nerve runs from the lateral aspect of the dural sac to the intervertebral foramen in a tubular canal of variable length; this canal is named the nerve root canal. Each ventral root (also named the anterior root, radix anterior, radix ventralis, or radix motoria) is attached to the spinal cord by a series of rootlets that emerge from the ventrolateral sulcus of the spinal cord. Each dorsal spinal root bears an ovoid swelling named the dorsal root (spinal) ganglion (DRG). A dermatome is the area of skin supplied by a single spinal nerve. Dermatomes have a segmental distribution represented as narrow bands of skin running almost horizontally along the trunk in a regular fashion.