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 two-week-old infant cries an average of one and a half hours every day. This increases to approximately three hours per day when the child is about six weeks old. By the time children are twelve weeks old, their daily crying has decreased dramatically and averages less than one hour. This same basic pattern of crying is present among children from a wide range of cultures throughout the world. It appears to be wired into the nervous system of our species.”
—Lawrence Kutner (20th century)
“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)
“He was the finest of our happy men;
He had all joys, he never thought of death;
He fiddled sometimes with his mind, and then
Shook off the tremor like a nervous wren....”
—Allen Tate (18991979)
“There are obvious places in which government can narrow the chasm between haves and have-nots. One is the public schools, which have been seen as the great leveler, the authentic melting pot. That, today, is nonsense. In his scathing study of the nations public school system entitled Savage Inequalities, Jonathan Kozol made manifest the truth: that we have a system that discriminates against the poor in everything from class size to curriculum.”
—Anna Quindlen (b. 1952)