Peripheral nervous system

Peripheral nervous system
The Human Nervous System. Blue is PNS while yellow is CNS.
Identifiers
Acronym(s)	PNS
TA	A14.2.00.001
FMA	9903
Anatomical terms of neuroanatomy []

The peripheral nervous system (PNS) is the part of the nervous system that 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, essentially serving as a communication relay going back and forth between the brain and spinal cord with the rest of the body. Unlike the CNS, the PNS is not protected by the bone of spine and skull, or by the blood–brain barrier, which leaves it exposed to toxins and mechanical injuries. The peripheral nervous system is mainly divided into the somatic nervous system and the autonomic nervous system. In the somatic 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 ten cranial nerve axons extend beyond the brain and are therefore considered part of the PNS. The Autonomic nervous system is an involuntary control of smooth muscle. The connection between CNS and organs allows the system to be in two different functional states: sympathetic and parasympathetic.

The peripheral nervous system is divided into somatic nervous system, sensory nervous systems, and autonomic nervous system. The somatic nervous system is under voluntary control, and transmits signals from the brain to end organs such as muscles. The sensory nervous system transmits signals from senses such as taste and touch (including fine touch and gross touch) to the spinal cord and brain. The autonomic nervous system is a 'self-regulating' system which influences the function of organs over which we have little or no voluntary control, such as the digestive system.