That part of the nervous system consisting of 12 pairs of cranial nerves (except for the optic nerve), 31 pairs of spinal nerves, their peripheral combinations, and the peripheral portions of the autonomic nervous system (consisting in turn of the sympathetic and parasympathetic nervous systems). The cranial nerves are connected directly to the brain, the spinal nerves at regular intervals to the spinal cord, and the autonomic system originates from both the brain and the spinal cord. Together, these three components of the PNS inform the central nervous system about events in the environment and transmit output from it to the body. Regeneration is possible in the PNS, but either not all or to a very limited extent in the CNS, due to the fact Schwann cells are able to induce the production of neurotrophic growth factors in the PNS. In the adult brain, extracelluar matrix molecules such as laminin and fibronectin are no longer expressed, and thus important adhesion molecules that can promote regeneration. Moreover, oligodendroglia (the myelinating cells of the CNS) express growth inhibitory molecules in the adult that prevent axon re-growth. One possible way of promoting the regeneration of damaged nerves in the CNS could be through the use of peripheral nerve grafts.
See Acetylcholine (AcH), Adhesion molecules, Autonomic nervous system (ANS), Central nervous system (CNS), Cranial nerves, Denervation, Dorsal root ganglia (DRG), Oligodendroglia, Nerve growth factor (NGF), Neural crest, Oligodendrocytes, Optic nerve, Parasympathetic nervous system (PNS), Schwann cells, Somatic nervous system (SNS), Sympathetic nervous system (SNS)