The Peripheral Nervous System (PNS)

  includes all the nerves outside the brain and spinal cord. It connects the Central Nervous System (CNS) to the rest of the body.

 

The PNS carries information:

 

From the body to the brain and spinal cord (sensory information)

From the brain and spinal cord to the muscles and organs (motor information)

 

Without the peripheral nervous system, the brain would not be able to communicate with the rest of the body.

 

The Two Main Divisions of the Peripheral Nervous System

 

The peripheral nervous system has two main divisions:

 

Somatic Nervous System

Autonomic Nervous System

Somatic Nervous System

 

The Somatic Nervous System controls voluntary movements. These are actions that you choose to perform consciously.

 

Examples include:

 

Walking

Talking

Writing

Picking up objects

Smiling

Running

 

The somatic nervous system also carries sensory information from the skin, muscles, and joints to the brain.

 

Examples include feeling:

 

Heat

Cold

Pain

Pressure

Touch

Autonomic Nervous System (ANS)

 

The Autonomic Nervous System (ANS) controls the body's automatic (involuntary) functions. These happen without us having to think about them.

 

The autonomic nervous system controls:

 

Heartbeat

Breathing

Digestion

Blood pressure

Sweating

Body temperature

Pupil size

Saliva production

Bladder function

 

These functions continue automatically whether we are awake or asleep.

 

The Three Divisions of the Autonomic Nervous System

 

The autonomic nervous system is divided into three parts:

 

Sympathetic Nervous System

Parasympathetic Nervous System

Enteric Nervous System

Sympathetic Nervous System

 

The Sympathetic Nervous System prepares the body to respond to stress, danger, or emergencies.

 

This is known as the "fight, flight, or freeze" response.

 

When activated, it:

 

Increases heart rate

Increases breathing rate

Raises blood pressure

Dilates (widens) the pupils

Sends more blood to the muscles

Slows digestion

Releases adrenaline

Increases alertness

 

This system helps us react quickly in dangerous situations.

 

Example

 

If you suddenly hear a loud noise behind you:

 

Your heart beats faster.

Your breathing speeds up.

Your muscles tense.

You become more alert.

Parasympathetic Nervous System

 

The Parasympathetic Nervous System helps the body recover after stress.

 

It is often called the "rest and digest" system.

 

It:

 

Slows the heart rate

Slows breathing

Lowers blood pressure

Stimulates digestion

Conserves energy

Helps the body relax

Supports healing and recovery

 

The sympathetic and parasympathetic systems work together to keep the body in balance.

 

Enteric Nervous System

 

The Enteric Nervous System (ENS) is sometimes called the "second brain."

 

It is a large network of nerves located in the digestive tract.

 

It controls:

 

Digestion

Movement of food through the intestines

Release of digestive enzymes

Blood flow to the digestive organs

Communication between the gut and the brain

 

Although it communicates with the brain, it can also function independently.

 

Visceral Nervous System

 

The term visceral nervous system refers to the nerves that supply the body's internal organs (viscera).

 

These nerves help control:

 

The heart

Lungs

Stomach

Intestines

Liver

Kidneys

Bladder

 

Most visceral functions are controlled automatically by the autonomic nervous system.

 

Sensory (Afferent) Nerves

 

Afferent nerves are also called sensory nerves.

 

Their job is to carry information toward the brain and spinal cord.

 

They detect information from:

 

Eyes

Ears

Skin

Nose

Tongue

Muscles

Internal organs

 

Examples include sensing:

 

Pain

Temperature

Touch

Pressure

Balance

Hunger

Stretching of muscles

 

Afferent = Arrives at the brain.

 

Motor (Efferent) Nerves

 

Efferent nerves are also called motor nerves.

 

Their job is to carry instructions away from the brain and spinal cord to the muscles, glands, and organs.

 

They control:

 

Muscle movement

Gland activity

Heart function

Digestion

Breathing

Blood vessel contraction and relaxation

 

Efferent = Exits the brain.

 

Ganglia

 

Ganglia are clusters of neuron (nerve cell) bodies located in the Peripheral Nervous System (PNS).

 

They act as important communication and processing centers between the peripheral nerves and the central nervous system.

 

Functions of Ganglia

Relay Signals

 

Ganglia act as relay stations where nerve impulses pass from one neuron to another.

 

They help transmit messages between the peripheral and central nervous systems.

 

Processing Information

 

Ganglia process and organize sensory information before sending it to the brain or spinal cord.

 

This helps the body respond more quickly to changes in the environment.

 

Types of Ganglia

 

There are two main types of ganglia.

 

Sensory Ganglia

 

These contain the cell bodies of sensory neurons.

 

They carry information such as:

 

Touch

Pain

Temperature

Pressure

Body position

 

to the brain and spinal cord.

 

Autonomic Ganglia

 

These belong to the autonomic nervous system.

 

They help regulate automatic body functions, including:

 

Heart rate

Digestion

Blood pressure

Breathing

Sweating

Integration of Motor Functions

 

Ganglia help coordinate motor signals before they reach muscles and organs.

 

This allows smooth movement and proper control of many body systems.

 

Summary Table

Structure Main FunctionThe 

Peripheral Nervous System (PNS) connects the brain and spinal cord to the rest of the body. The 

Somatic Nervous System  Controls voluntary movement and carries sensory information.

The autonomic nervous system (ANS) controls involuntary body functions.

The sympathetic nervous system prepares the body for "fight, flight, or freeze."

The parasympathetic nervous system helps the body relax, recover, and digest food.

The enteric nervous system controls the digestive system and communicates with the brain.The 

Visceral Nervous System supplies nerves to the body's internal organs.

Afferent (Sensory) Nerves carry sensory information to the brain and spinal cord.

Efferent (Motor) Nerves carry commands from the brain and spinal cord to muscles and organs.

Ganglia: Clusters of nerve cell bodies in the PNS that relay, process, and coordinate nerve signals.

Key Points

The Peripheral Nervous System (PNS) connects the brain and spinal cord to the rest of the body.

The PNS is divided into the Somatic Nervous System and the Autonomic Nervous System.

The Somatic Nervous System controls voluntary movements and carries sensory information.

The Autonomic Nervous System controls involuntary functions such as heartbeat, breathing, digestion, and blood pressure.

The autonomic nervous system has three divisions: the Sympathetic, Parasympathetic, and Enteric Nervous Systems.

Afferent (sensory) nerves carry information to the brain and spinal cord, while efferent (motor) nerves carry commands away from the brain and spinal cord.

Ganglia are clusters of nerve cell bodies in the peripheral nervous system that relay, process, and coordinate nerve signals, helping the body respond efficiently to both internal and external changes.