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
Famous quotes containing the words nervous system, peripheral, nervous and/or system:
“A car can massage organs which no masseur can reach. It is the one remedy for the disorders of the great sympathetic nervous system.”
—Jean Cocteau (18891963)
“If we are to change our world view, images have to change. The artist now has a very important job to do. Hes not a little peripheral figure entertaining rich people, hes really needed.”
—David Hockney (b. 1937)
“The knocking out of a pipe can be made almost as important as the smoking of it, especially if there are nervous people in the room. A good, smart knock of a pipe against a tin wastebasket and you will have a neurasthenic out of his chair and into the window sash in no time.”
—Robert Benchley (18891945)
“We recognize caste in dogs because we rank ourselves by the familiar dog system, a ladderlike social arrangement wherein one individual outranks all others, the next outranks all but the first, and so on down the hierarchy. But the cat system is more like a wheel, with a high-ranking cat at the hub and the others arranged around the rim, all reluctantly acknowledging the superiority of the despot but not necessarily measuring themselves against one another.”
—Elizabeth Marshall Thomas. Strong and Sensitive Cats, Atlantic Monthly (July 1994)