The peripheral nervous system (PNS) comprises nerve fibers and ganglia located outside of the brain and spinal cord, including 11 pairs of cranial nerves and 31 pairs of spinal nerves. The spinal (or somatic) nerves originate as dorsal and ventral spinal nerve rootlets at their junction with the spinal cord. The dorsal spinal nerve roots contain afferent (sensory) nerve fibers and their cell bodies, which are located in the dorsal root ganglia (DRG). The ventral spinal nerve roots contain efferent (motor) fibers whose cell bodies are located in the ventral horn of the spinal cord. The dorsal and ventral roots merge to form the spinal nerve, which exits the spinal column through the intervertebral foramen. Upon exiting the spine, the nerve divides into dorsal and ventral rami, which may branch further and mix with other nerve fibers to form plexuses (e.g., brachial plexus) and eventually form distinct peripheral nerves and their branches.