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The peripheral nervous system (PNS) is critical for connecting the central nervous system (CNS) to the rest of the body. It is essential for bodily functions such asmovement, sensation, and autonomic processes.
What does the PNS do?
The PNS has many essential functions throughout the body:
Structures of the Peripheral Nervous System
The PNS can be divided into two components: thesomatic nervous systemand theautonomic nervous system:
Somatic Nervous System
The somatic nervous system (SNS)is associated with activities traditionally thought of as conscious or voluntary.
It is involved in the relay of sensory and motor information to and from the CNS; therefore, it consists ofmotor neurons and sensory neurons:
Autonomic Nervous System
The autonomic nervous system (ANS)coordinates involuntary behaviors such as heart rate, breathing, and digestion. This system allows these important functions to occur without conscious thought, so they work automatically.
The ANS is further divided into two components:
The Autonomic Nervous System Has Two Main Divisions:Sympathetic and Parasympathetic
Thesympathetic nervous systemmostly comes into play when the body needs to respond to threatening stimuli. This response is called thefight-or-flight response.
It slows bodily processesthat are less important in emergencies, such as digestion.
When this happens, the system will reduce the heart rate, stop the body from sweating, decrease blood flow, and constrict the pupils – allowing us to reach a state of rest.
The two systems have complementary functions, operating in tandem to maintain the body’shomeostasis(a state of equilibrium).
Central nervous system vs peripheral nervous system
The central nervous system(CNS) andperipheral nervous system(PNS) serve distinct but complementary roles.
The PNS comprises nerves branching throughout the body, lacking bony protection and thus more vulnerable to injury.
While the CNS processes and makes decisions, the PNS functions as a messenger network through sensory and motor neurons.
CNS neurons alsohave limited regenerative capacity, making injuries often permanent. PNS neurons, however, can regenerate under certain conditions, allowing for potential recovery fromperipheral nerve damage.
Nerves in the Peripheral Nervous System
The PNS is made up of nerve cells (neurons) that carry messages back and forth between the CNS and the muscles, organs, and senses in the body’s periphery.
Within the PNS, some nerves are attached to the spinal cord (spinal nerves), and others are attached directly to the brain (cranial nerves).
Spinal nerves
Spinal nervescarry signals from receptors around the body to the spinal cord. These signals are thentransmitted to the brain for processing.
These also transmit motor signals from the brain to the body’s muscles and glands, so the brain’s directions can be carried out quickly.
The PNS is made up of31 pairs of spinal nerves, which radiate out from the spinal cord, operating different locations of the body:
These nerves divide and subdivide to form a networkconnecting the spinal cord to every body part.
The longest nerve in the human body,the sciatic nerve(from the lumbar region), networks off until it reaches the tips of the toes, measuring up to a meter or more in length.
Cranial nerves
Thecranial nervesprimarily coordinate themuscle and sense receptors of the head and neck.
These nerves are different from the spinal nerves as they do not enter through the spinal cord to reach the brain, instead, they are directly linked to the brain.
Cranial nerves allowsensory informationto be transmitted from the organs of the brain (ears, eyes, nose, and mouth), as well as conveyingmotor informationfrom the brain to these organs.
For instance, when eating food, the brain will transmit motor messages through the nerves to move the mouth in order to chew and swallow. When tasting the food, the sensory information gets sent back to the brain through a set of cranial nerves.
There are 12 pairs of cranial nerves attached to the brain:
SourcesDorland, W. A. N. (2011).Dorland’s Illustrated Medical Dictionary E-Book. Elsevier Health Sciences.Eyesenck, M. W. (2012).Simply Psychology. New York: Taylor & Francis.Goldstein, D. S. (2010).Adrenal responses to stress.Cellular and Molecular Neurobiology, 30(8), 1433-1440.Martin, G. N., Carlson, N. R., & Buskist, W. (2009).Psychology, 4th European edition. Harlow: Pearson Education, 723-725.
Sources
Dorland, W. A. N. (2011).Dorland’s Illustrated Medical Dictionary E-Book. Elsevier Health Sciences.
Eyesenck, M. W. (2012).Simply Psychology. New York: Taylor & Francis.
Goldstein, D. S. (2010).Adrenal responses to stress.Cellular and Molecular Neurobiology, 30(8), 1433-1440.
Martin, G. N., Carlson, N. R., & Buskist, W. (2009).Psychology, 4th European edition. Harlow: Pearson Education, 723-725.
The Peripheral Nervous System (PNS) connects the Central Nervous System (CNS) to the rest of the body, including limbs and organs. It consists of nerves and ganglia outside the brain and spinal cord. The PNS is responsible for transmitting information between the CNS and the body’s tissues. It has two main components: the somatic nervous system, which controls voluntary actions, and the autonomic nervous system, which manages involuntary functions like heartbeat and digestion.
Saul McLeod, PhD
BSc (Hons) Psychology, MRes, PhD, University of Manchester
Saul McLeod, PhD., is a qualified psychology teacher with over 18 years of experience in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology.
Olivia Guy-Evans, MSc
BSc (Hons) Psychology, MSc Psychology of Education
Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.
