The peripheral nervous system (PNS) is the part of the nervous system that lies outside of the brain and spinal cord, known collectively as the central nervous system (CNS). The nerves in the PNS connect the CNS to sensory organs (such as the eye and ear), other organs of the body, muscles, blood vessels, and glands.

The PNS includes the 12 cranial nerves, the spinal nerves and roots, and what are called the autonomic nerves. The autonomic nerves are concerned with automatic functions of the body – specifically with the regulation of the heart muscle, the tiny muscles lining the walls of blood vessels, and glands.