The Peripheral Nervous System

The peripheral nervous system (PNS) is made up of all the nerve fibres, nerve trunks and ganglia (clusters of neuron cell bodies) that lie outside the brain and spinal cord, and its job is to connect the central nervous system to every receptor and every effector organ in the body.

The PNS has two structural components. Twelve pairs of cranial nerves arise directly from the base of the brain and mainly supply structures of the head and neck — for example, the olfactory nerve carries smell information and the optic nerve carries visual information from the eye — although one cranial nerve, the vagus nerve, is a notable exception in that it travels far beyond the head and neck to supply many of the visceral organs of the thorax and abdomen, including the heart, lungs and much of the gut, and carries a large proportion of the parasympathetic outflow of the autonomic nervous system. Thirty-one pairs of spinal nerves arise at regular intervals from the spinal cord, one pair for each segment of the cord (named and numbered by the region of the vertebral column they emerge from — cervical, thoracic, lumbar, sacral and coccygeal); unlike most cranial nerves, every spinal nerve is a mixed nerve, containing both sensory (afferent) fibres carrying information into the cord and motor (efferent) fibres carrying commands out to muscles and glands. …