Peripheral nervous system

The peripheral nervous system (PNS) consists of the nerves (cranial nerves III-XII and spinal) and their related ganglia outside the central nervous system (CNS). The latter comprising the brain and spinal cord. The central nervous system and peripheral nervous system 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 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 spinal cord to communicate with the viscera and musculoskeletal system.

The peripheral nervous system has two main elements:

• somatic nervous system (voluntary functions)

  • afferent motor innervation of skeletal muscles

  • efferent sensory innervation of touch, pain, temperature, and position

• autonomic nervous system (involuntary functions)

  • afferent motor innervation of glands, smooth and cardiac muscles

  • efferent sensory innervation from the viscrea