Peripheral Nervous System Study Guide

Peripheral nervous system comprises nerves branching out from the brain and spinal cord. Peripheral systems form a communication network between the CNS and the body parts.


The body's governing mechanism is the nervous system, which comprises nerve cells and organs. The central nervous system and the peripheral nervous system are two components of the nervous system. The brain and spinal cord make up the central nervous system. However, the peripheral nervous system is the network of nerves that link the brain and spinal cord.

What is the Peripheral Nervous System?

The peripheral nervous system, or PNS, is nearly completely comprised of nerves. Spinal nerves and cranial nerves are the two main classifications. The autonomic and somatic nervous systems are two functional divisions of the PNS. Both of these may be split further, with autonomic being divided further into the sympathetic and parasympathetic nervous system and the somatic being divided into sensory and motor divisions.

Nerve Categorization

Based on where they emerge from the CNS, nerves are categorized as 'cranial' or 'spinal.' Spinal nerves exit the CNS via the spinal cord, whereas cranial nerves originate from the brain. The peripheral nervous system comprises 43 paired nerves, which include 12 pairs of cranial nerves and 31 pairs of spinal nerves.

Central Nervous System Source

What is the Somatic Nervous System?

The somatic nervous system is comprised of both cranial and spinal nerves. The cranial nerves supply the head and face with voluntary motor control and sensation. On the other hand, spinal nerves provide sensation to the trunk and limbs.

Afferent or sensory neurons send information to the CNS, whereas efferent or motor neurons carry impulses away. Afferent neurons have a variety of stimuli from sensory receptors. They convey general feelings like touch, pain, temperature, and spatial location. Some can also communicate additional sensory data, such as the senses of smell, vision, hearing, and balance.

On the other hand, efferent neurons or motor neurons provide general neurological information to effector organs such as skeletal muscles, visceral organs, and glands. They are in charge of starting both voluntary and involuntary motor activities, including muscle contraction and gland secretion.

What is the Autonomic Nervous System?

As it is involuntary, we have no cognitive control over it. Smooth muscles, blood arteries, glands, and internal organs get sensory and motor innervation from the ANS. As a result, it regulates visceral and glandular activities in a coordinated manner, contributing to homeostasis.

The sympathetic and parasympathetic branches of the autonomic nervous system (ANS) are the two primary branches. The sympathetic division of the brain prepares the body for times of greater physical activity by controlling blood vessels, dilation of pupils, increased heart rate and blood pressure, and decreased bowel movement (peristalsis).

The parasympathetic division helps the body save energy by performing processes such as 'rest and digest,' eating, and breeding. Slowing the cardiovascular system, stimulating glandular secretion, and increasing peristalsis are used to accomplish this. The PNS likewise controls sexual arousal and crying.


  • The network of nerves that link the brain and spinal cord is the peripheral nervous system.
  • The autonomic and somatic nervous systems are two functional divisions of the PNS.
  • Autonomic can be divided into the sympathetic and parasympathetic nervous systems and the somatic nervous system is divided into sensory and motor divisions.
  • The difference between sensory neurons and motor neurons is that the former carry impulse toward the CNS while the latter carry impulses away.


1. What is the peripheral nervous system, and what are its functions?

The network of nerves that link the brain and spinal cord is the peripheral nervous system. Carrying sensory and motor impulses from the target place in the body to the CNS and vice-versa, controlling involuntary functions like increasing or decreasing pulse rate, controlling bowel movements, and glandular secretions of the digestive system are a few functions of PNS.

2. What are the 4 functions of the peripheral nervous system?

  • Convey general feelings like touch, pain, temperature.
  • Receiving additional special sensory data, such as the senses of smell, vision, hearing, and balance.
  • Sensory input from many sections of the body is combined and processed here.
  • Conveying motor impulses to voluntary muscles.

3. What are PNS and CNS, and how do they work together?

  • Synapses develop between neurons, allowing both CNS and PNS to communicate. The peripheral nervous system (PNS) receives information through sensory neurons. It transfers the information to the central nervous system (CNS) for processing.

  • PNS stands for the peripheral nervous system, whereas CNS stands for the central nervous system. CNS comprises the brain and the spinal cord. All the information is processed and responses are generated. At the same time, PNS connects the CNS to all other body parts and helps deliver the impulses.

4. What are the 3 main components of the peripheral nervous system?

  • Sensory: Receives sensory inputs like smell, touch, taste and transfers this to the CNS
  • Motor: Carries impulses from the CNS to the voluntary muscle fibers to stimulate movement.
  • Autonomic: Responsible for involuntary functions like pulse rate, digestion, blood pressure.

5. What are ganglia and their functions?

  • A ganglion is a group of neurons found in the peripheral nervous system's (PNS) voluntary and autonomic branches. Ganglia act as synaptic nodes connecting neurons. The impulse reaches the ganglia, stimulates the ganglia's neuron, and then leaves the ganglia.
  • Involuntary smooth muscles, cardiac muscles, and glands are all innervated by ganglia. The autonomic ganglia detect sensory cues such as blood pressure, salinity, and PH.

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  1. Peripheral Nervous System Anatomy. https://emedicine.medscape.com/article/1948687-overview. Accessed on 25 Nov, 2021.
  2. Peripheral Nervous System. https://flexbooks.ck12.org/cbook/ck-12-biology-flexbook-2.0/section/13.16/primary/lesson/peripheral-nervous-system-bio/. Accessed on 25 Nov, 2021.
  3. The Peripheral Nervous System. https://training.seer.cancer.gov/anatomy/nervous/organization/pns.html. Accessed on 25 Nov, 2021.