The peripheral nervous system (PNS) consists of the nerves (cranial nerves III-XII and spinal nerves) and their related ganglia outside the central nervous system (CNS), the latter comprising the brain and the spinal cord. The central and the peripheral nervous systems together form the nervous system.
Unlike the central nervous system, the peripheral nervous system is not protected by:
a blood-brain barrier, leaving it much more susceptible to toxins and other potentially harmful influences
the skull and the vertebral column, unlike the brain and spinal cord
NB: cranial nerves I and II are considered part of the CNS
Function
The main function of the peripheral nervous system is to allow the brain and the spinal cord to communicate with the viscera and the musculoskeletal system.
The peripheral nervous system has two main elements:
-
somatic nervous system (voluntary functions)
efferent (motor) innervation of skeletal muscles
afferent (sensory) innervation of touch, pain, temperature, and position
-
autonomic nervous system (involuntary functions)
efferent (motor) innervation of glands, smooth and cardiac muscles
afferent (sensory) innervation from the viscera