The Peripheral Nervous System (PNS) is the body’s internal messenger service. Its function is to carry information between the Central Nervous System and the rest of the body.
While the Central Nervous System consists of the brain and the spinal cord, the PNS contains only nerves. Thirty-one pairs of nerves called Spinal Nerves carry information to and from the spinal cord. Another twelve pairs of nerves called Cranial Nerves carry information to and from the brain.
Data traveling to the brain and spinal cord for analysis travel what is called a sensory or afferent pathway. Once the data is analyzed, the Central Nervous System’s instructions travel a motor or efferent pathway back to the proper part of the body.
An interesting note is that because nerves are actually bundles of axons (also called nerve fibers), a single nerve can serve as both a sensory and motor pathway, with information going both to and from the CNS. However, some nerves are exclusively either sensory or motor.
Information travels these nerve pathways by way of electrical impulses. Some axons are covered by a white substance called Myelin which increases the speed of impulses along the axon. These axons are called myelinated axons. The impulses travel from one neuron to the next at junctions called synapses.
The Peripheral Nervous System has two parts: the Somatic nervous system and the Autonomic nervous system.
Somatic Nervous System: This branch of the PNS handles the information of which we are consciously aware. For instance, from feeling an itch right through to scratching it would all involve the Somatic system.
Autonomic Nervous System: This PNS branch handles the information we are not consciously aware of. This is where all of our body’s internal functions, such as digestion and heartbeat are handled.
The Autonomic nervous system can also be divided into two parts: the Sympathetic system and the Parasympathetic system. These two systems actually work in opposition to each other to give our bodies balance.
In general terms, the sympathetic system handles the fight or flight response and revs our systems up, increasing heartbeat, etc. The parasympathetic system calms us down and is in charge of relaxation, for instance slowing our heartbeat back down to normal after a scare.
In a very simplistic summary, the human nervous system works as follows. The body has Receptors in sense organs and internal body parts that gather information about our environment, both inside and outside our bodies. This gathered information travels the nerves of the Peripheral Nervous System to the spinal cord and / or the brain (the Central Nervous System) for processing. Instructions are then sent back through the PNS to the necessary part of the body.
All done, literally, in the blink of an eye.
The World Book Encyclopedia 2005
Macmillan Encyclopedia of Health 1993