Peripheral Nervous System
Nerves that are not part of the brain, spinal cord or retina, normally found in the extremities (e.g., arms, legs).
The peripheral nervous system (PNS) is not part of the brain, spinal cord or retina [although the cell bodies (control centers) for nerves that extend into the extremities (including arms and legs) are anchored in the brain and spinal cord]. The PNS is not protected by bone or the blood-brain barrier, leaving it exposed to toxins and mechanical injuries. Normally, peripheral nerves either control voluntary muscle movement (i.e., controllable processes like lifting an arm) or are involved in involuntary processes, like breathing, heart rate, etc. The retina is not considered to be part of the PNS.