MedTerms Medical Dictionary

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Nervous system, peripheral (PNS): That portion of the nervous system that is outside the brain and spinal cord.

The peripheral nervous system (PNS) is one of the two major divisions of the nervous system. The other is the central nervous system (CNS) which is made up of the brain and spinal cord.

The nerves in the peripheral nervous system (PNS) connect the central nervous system (CNS) to sensory organs (such as the eye and ear), other organs of the body, muscles, blood vessels and glands.

The peripheral nerves include the 12 cranial nerves, the spinal nerves and roots, and what are called the autonomic nerves. The autonomic nerves are concerned with automatic functions of the body. Specifically, autonomic nerves are involved with the regulation of the heart muscle, the tiny muscles lining the walls of blood vessels, and glands.

"Peripheral" in anatomy and medicine (as elsewhere) is the opposite of "central." It means situated away from the center. The word "peripheral" comes from the Greek "peripheria" ("peri-", around or about + "pherein", to bear, carry). An IV (intravenous) catheter is a peripheral line.

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