Spinal Nerves

There are 31 pairs of spinal nerves (62 total). The following discussion traces a spinal nerve as it emerges from the spinal column:

A spinal nerve emerges at two points from the spinal cord, the ventral and dorsal roots.

  • The ventral and dorsal roots merge to form the whole spinal nerve.

  • The spinal nerve emerges from the spinal column through an opening (intervertebral foramen) between adjacent vertebrae. This is true for all spinal nerves except for the first spinal nerve (pair), which emerges between the occipital bone and the atlas (the first vertebra).

  • Outside the vertebral column, the nerve divides into the following branches:

    • The dorsal ramus contains nerves that serve the dorsal portions of the trunk.

    • The ventral ramus contains nerves that serve the remaining ventral parts of the trunk and the upper and lower limbs.

    • The meningeal branch reenters the vertebral column and serves the meninges and blood vessels within.

    • The rami communicantes contain autonomic nerves that serve visceral functions.

  • Some ventral rami merge with adjacent ventral rami to form a plexus, a network of interconnecting nerves. Nerves emerging from a plexus contain fibers from various spinal nerves, which are then carried together to some target location.

An area of the skin that receives sensory stimuli that pass through a single spinal nerve is called a dermatome. Dermatomes are illustrated on a human figure with lines that mark the boundaries of the area where each spinal nerve receives stimuli.