Definition, Parts and FunctionBy Olivia Guy-Evans, published April 23, 2021 Show by Saul Mcleod, PhD The nervous system of the body is split into two parts: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS is made up of the brain and the spinal cord components. The PNS is all the nerves that branch out from the CNS components and extend to other parts of the body – to the sense organs, muscles, and glands. The PNS connects the CNS to the rest of the body. The primary function of the peripheral nervous system is to connect the brain and spinal cord to the rest of the body and the external environment. The peripheral nervous system transmits information to and from the CNS. This is accomplished through nerves that carry information from sensory receptors in the eyes, ears, skin, nose and tongue, as well as stretch receptors and nociceptors in muscles, glands and other internal organs. The sense organs are able to detect changes in the environment and relay information through the sensory nerves to the CNS. The brain can then send signals through the nerves to the muscles, resulting in the muscles to move in response. Therefore, there is always a stream of incoming and outgoing information between the PNS, CNS, and the body through the form of nerve impulses. The main functions of the PNS are voluntary movements such as chewing food, walking, and facial expressions. The PNS also regulates autonomic functions such as breathing, heart rate, and digesting – the unconscious bodily behaviors. The PNS is thus especially important for humans to survive. Unlike the CNS which is protected by the skull and the vertebrae of the spine, the nerves, and cells of the PNS are not enclosed by bones. This makes the PNS more susceptible to damage by trauma. Parts of the PNS
The somatic nervous system (SNS) and the autonomic nervous system (ANS) are both part of the peripheral nervous system. The SNS controls voluntary actions such as walking. The ANS is responsible for the control of vital functions such as heart beat and breathing. It is also involved in the acute stress response where it works with the endocrine system to prepare the body to fight or flight. Somatic Nervous SystemThe somatic nervous system is associated with activities traditionally thought of as conscious or voluntary. The somatic nervous system is key for carrying messages throughout the body, in order to initiate and control movement. This system processes sensory information from external stimuli (e.g. through hearing, sight, and touch) as well as motor information, which then carries signals to and from the CNS. This is so it can interpret sensory information and control voluntary movements.
As well as regulating voluntary movements, the somatic nervous system is also responsible for reflexes. This is an involuntary muscle response being controlled by a reflex arc, which is a neural pathway. For instance, when touching a very hot surface, the sensory neuron activity will be skipped and instead the brain will send almost instantaneous motor signals to move the hand away from the surface quickly. Autonomic Nervous SystemThe autonomic nervous system is responsible for coordinating involuntary behaviors such as heart rate, breathing, and digestion. This system allows these important functions to take place without conscious thought, so they work automatically.
Sympathetic Nervous System The sympathetic nervous system mostly comes into play during times when the body feels it needs to respond to threatening stimuli. This response is called the fight-or-flight response. During a threatening situation, this system will respond by increasing heart rate, activate sweat glands, increase blood flow, and dilate the pupils. It slows bodily processes that are less important in emergencies such as digestion. Parasympathetic Nervous System The parasympathetic nervous system relaxes the individual once the emergency has passed. The parasympathetic system aims to maintain normal bodily functions by decreasing activity/maintaining it. 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 parasympathetic ANS leads to decreased arousal.
Nerves of the PNSThe peripheral nervous system is made up of thick bundles of axons, called nerves, carrying messages back and forth between the CNS and the muscles, organs, and senses in the periphery of the body (i.e., everything outside the CNS). The nerve cells (or neurons) are the information processing units of the brain that are responsible for sending, receiving, and transmitting signals throughout the body. The neurons are essentially the cells which make up the central nervous system and the peripheral nervous system. The structure of neurons allows it to receive and carry messages effectively to other neurons and throughout the body. It contains a soma (cell body), which is the core of the neuron, responsible for ensuring that everything is functioning efficiently. The axon is a tail-like structure of the neuron which functions in carrying signals away from the soma to the end of the neuron, for the purpose of transmitting signals to other neurons. The dendrites of the neurons are tree-root shaped, located at the end of the neuron. Their function is to receive and pass on information through their synapses to other neurons nearby. The nerves are essentially bundles of thousands of individual axons all wrapped in a protective membrane in the PNS. Messages are sent along each of the axons to the peripheral organs of the body and send back information to the CNS. Each axon within the nerve is an extension of an individual neuron. Within the PNS, there are some nerves that are attached to the spinal cord (spinal nerves) and others which are attached directly to the brain (cranial nerves). Spinal nervesSpinal nerves are relatively large nerves that serve all of the body below the neck, conveying sensory and motor information from the body and carrying messages to the muscles and glands. The spinal nerves carry signals from receptors around the body to the spinal cord. These signals are then transmitted 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.
Each spinal nerve exits the spinal cord by traveling through openings at the right and left sides of the vertebrae of the spine. These nerves divide and subdivide to form a network connecting the spinal cord to every part of the body. 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 nervesThe cranial nerves primarily coordinate the muscle and sense receptors of the head and neck. These nerves are different to 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 allow sensory information to transmit from the organs of the brain (ears, eyes, nose, and mouth), as well as conveying motor information from 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.
About the AuthorOlivia Guy-Evans obtained her undergraduate degree in Educational Psychology at Edge Hill University in 2015. She then received her master’s degree in Psychology of Education from the University of Bristol in 2019. Olivia has been working as a support worker for adults with learning disabilities in Bristol for the last four years. How to reference this article:How to reference this article:Guy-Evans, O. (2021, April 28). Peripheral nervous system (PNS) definition, parts and function. Simply Psychology. www.simplypsychology.org/peripheral-nervous.system.html Article 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. Guy-Evans, O. (2021, Feb 15). What is a neuron? Function, parts, structure, and types. Simply Psychology. www.simplypsychology.org/neuron.html Martin, G. N., Carlson, N. R., & Buskist, W. (2009). Psychology, 4th European edition. Harlow: Pearson Education, 723-725. Home | About Us | Privacy Policy | Advertise | Contact Us Simply Psychology's content is for informational and educational purposes only. Our website is not intended to be a substitute for professional medical advice, diagnosis, or treatment. © Simply Scholar Ltd - All rights reserved
How is the peripheral nervous system structured or divided?The peripheral nervous system consists of the nerves that branch out from the brain and spinal cord. These nerves form the communication network between the CNS and the body parts. The peripheral nervous system is further subdivided into the somatic nervous system and the autonomic nervous system.
What are the 3 primary divisions of the PNS?Types of nerve signals. Sensory: These nerves carry information to your brain and spinal cord. ... . Motor: These nerves carry command signals from your brain to various parts of your body. ... . Autonomic: These nerves control the automatic functions of the organs and systems in your body.. |