The peripheral nervous system includes the nerves and ganglia that are outside of the central nervous system.  The peripheral nervous system is made up of two divisions. The somatic nervous system and the autonomic system. Each part of this system plays a vital role in how information is communicated throughout the body.

Pritish Kumar gives a brief Illustration of Peripheral nervous system:

What Is the Peripheral Nervous System?

The nervous system is divided into two parts. The central nervous system and the peripheral nervous system. The central nervous system (CNS) includes the brain and spinal cord. While the peripheral nervous system includes all of the nerves that branch out from the brain and spinal cord and extend to other parts of the body including muscles and organs.

The primary role of the PNS is to connect the CNS to the organs, limbs, and skin. These nerves extend from the central nervous system to the outermost areas of the body. The peripheral system allows the brain and spinal cord to receive and send information to other areas of the body. Which allows us to react to stimuli in our environment.

Central and peripheral nervous system

Structures of the Peripheral Nervous System

The peripheral nervous system itself is divided into two parts. The somatic nervous system and the autonomic nervous system.

Each of these components plays a critical role in how the peripheral nervous system operates.

The Somatic Nervous System

The somatic system is the part of the peripheral nervous system responsible for carrying sensory and motor information to and from the central nervous system. Somatic nervous system derives its name from the Greek word soma, which means “body.”

The somatic system is responsible for transmitting sensory information as well as for voluntary movement. This system contains two major types of neurons:

Motor neurons: Also called efferent neurons, motor neurons carry information from the brain and spinal cord to muscle fibers throughout the body. These motor neurons allow us to take physical action in response to stimuli in the environment.

Sensory neurons: Also called afferent neurons, sensory neurons carry information from the nerves to the central nervous system. It is these sensory neurons that allow us to take in sensory information and send it to the brain and spinal cord.

The Autonomic Nervous System

The autonomic system is the part of the peripheral nervous system that’s responsible for regulating involuntary body functions, such as blood flow, heartbeat, digestion, and breathing.

In other words, it is the autonomic system that controls aspects of the body that are usually not under voluntary control. This system allows these functions to take place without needing to consciously think about them happening. The autonomic system is further divided into two branches:

Parasympathetic system: This helps maintain normal body functions and conserve physical resources. Once a threat has passed, this system will slow the heart rate, slow breathing, reduce blood flow to muscles, and constrict the pupils. This allows us to return our bodies to a normal resting state.

Sympathetic system: By regulating the flight-or-fight response, the sympathetic system prepares the body to expend energy to respond to environmental threats. When action is needed, the sympathetic system triggers a response by accelerating heart rate, increasing breathing rate, boosting blood flow to muscles, activating sweat secretion, and dilating the pupils.

Nerves in the Peripheral Nervous System

The PNS is composed of nerves that are responsible for carrying signals between the central nervous system and the parts of the body that lie outside the CNS. This includes information from the senses, organs, and muscles.

The axons of these nerve cells are bundled together and can be found throughout the body. Information is received by the dendrites of these cells, the information travels down the axon to the cell body. The message can then be communicated to other cells.

Nerves that make up the peripheral nervous system connect with either the spinal cord or brain in order to transmit information to the CNS.

Spinal Nerves

Spinal nerves are responsible for transmitting information from the muscles, organs, and glands to the spinal cord. There are 31 spinal nerves that branch out to different areas of the body from the spinal cord.

Cranial Nerves

The cranial nerves are responsible for the receptors found in the head and neck area. Instead of connecting with the spinal cord, these nerves travel directly to the brain. There are 12 pairs of cranial nerves that transmit motor and sensory information from areas including the face, mouth, eyes, nose, and ears.

Difference between the CNS and peripheral nervous system

The term peripheral nervous system (PNS) refers to any part of the nervous system that lies outside of the brain and spinal cord. The CNS is separate from the peripheral nervous system, although the two systems are interconnected.

There are a number of differences between the CNS and PNS; one difference is the size of the cells. The nerve axons of the CNS — the slender projections of nerve cells that carry impulses — are much shorter. PNS nerve axons can be up to 1 meter long (for instance, the nerve that activates the big toe) whereas, within the CNS, they are rarely longer than a few millimeters.

Another major difference between the CNS and PNS involves regeneration (regrowth of cells). Much of the PNS has the ability to regenerate; if a nerve in your finger is severed, it can regrow. The CNS, however, does not have this ability.