The peripheral nervous system (PNS, or occasionally PeNS) consists of the nerves and ganglia outside of the brain and spinal cord. The main function of the PNS is to connect the central nervous system (CNS) to the limbs and organs. Unlike the CNS, the PNS is not protected by the bone of spine and skull, or by the blood–brain barrier, leaving it exposed to toxins and mechanical injuries. The peripheral nervous system is divided into the somatic nervous system and the autonomic nervous system; some textbooks also include sensory systems. It is also a part of the nervous system.
The cranial nerves are part of the PNS with the exception of cranial nerve II, the optic nerve, along with the retina. The second cranial nerve is not a true peripheral nerve but a tract of the diencephalon. Cranial nerve ganglia originate in the CNS. However, the remaining eleven cranial nerve axons extend beyond the brain and are therefore considered part of the PNS.
Read more about Peripheral Nervous System: Specific Nerves and Plexi, Neurotransmitters
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