Divisions of the nervous system | AQA A-Level Psychology Revision

For 7182 specification, first teach in September 2025

AQA A-Level Psychology | Free Revision Notes

Estimated study time: 40 minutes

These Divisions of the nervous system A-Level Psychology revision notes explain how the body’s communication system is organised. You will examine the central nervous system, consisting of the brain and spinal cord, before exploring the peripheral nervous system and its somatic and autonomic divisions. Understanding this organisation provides the foundation for studying how sensory, relay and motor neurons communicate and how signals pass between neurons in AQA A-Level Psychology.

Learning Objectives 🎯

By the end of this revision page, you should be able to:

• Define the central nervous system.

• Describe the roles of the brain and spinal cord.

• Define the peripheral nervous system.

• Explain how the peripheral nervous system connects the central nervous system with the rest of the body.

• Distinguish between the somatic and autonomic nervous systems.

• Apply the divisions of the nervous system to unfamiliar situations.

Revision Notes 📚

Divisions of the nervous system A-Level Psychology revision overview

The nervous system is a communication system that allows information to travel between different parts of the body.

It enables an organism to:

1. Detect information from inside or outside the body.

2. Transmit that information.

3. Process the information.

4. Coordinate an appropriate response.

The nervous system is divided into two main parts:

• The central nervous system

• The peripheral nervous system

The peripheral nervous system is then divided into:

• The somatic nervous system

• The autonomic nervous system

Organisation of the nervous system

The structure can be represented as follows:

Nervous system
│
├── Central nervous system
│   ├── Brain
│   └── Spinal cord
│
└── Peripheral nervous system
    ├── Somatic nervous system
    └── Autonomic nervous system

A common examination task is to identify where each division belongs within this hierarchy.

The somatic and autonomic nervous systems are both divisions of the peripheral nervous system, not the central nervous system.

The central nervous system

The central nervous system, usually abbreviated to CNS, consists of:

• The brain

• The spinal cord

It is called central because it forms the main centre for processing information and coordinating responses.

The CNS receives information from the rest of the body and sends instructions back through the peripheral nervous system.

The brain

The brain processes information and coordinates behaviour.

It receives signals containing information about:

• The external environment

• Conditions within the body

• Current sensory experiences

It can then organise an appropriate response.

For example:

1. A person sees a pedestrian crossing the road.

2. Information reaches the brain.

3. The brain processes the situation.

4. An instruction is sent to move the person’s foot onto the brake pedal.

The brain is therefore part of the central system that interprets information and coordinates responses.

Specific functions associated with different brain areas are covered later through the functions of particular brain regions.

The spinal cord

The spinal cord is a long bundle of nervous tissue extending from the brain.

It provides an important communication route between the brain and the peripheral nervous system.

Information may travel:

• From the body towards the brain.

• From the brain towards muscles and other parts of the body.

The spinal cord is therefore not part of the peripheral nervous system. It belongs to the CNS alongside the brain.

The roles of the CNS

The CNS can be summarised as having three broad roles:

1. Receiving information

   
   

   Signals from the body enter the CNS.

2. Processing and coordinating

   
   

   The brain and spinal cord contribute to organising responses.

3. Sending instructions

   
   

   Signals leave the CNS and travel to parts of the body through the peripheral nervous system.

The pathways carrying these signals involve specialised sensory, relay and motor neurons.

The peripheral nervous system

The peripheral nervous system, usually abbreviated to PNS, consists of the nerves outside the brain and spinal cord.

Its central role is to connect the CNS with the rest of the body.

The PNS carries:

• Information from the body towards the CNS.

• Instructions from the CNS towards the body.

Without the PNS, the brain and spinal cord could not communicate effectively with sensory receptors, muscles and internal organs.

The PNS as a communication link

The relationship between the CNS and PNS can be represented as:

Body → peripheral nervous system → central nervous system

and

Central nervous system → peripheral nervous system → body

For example:

1. Sensory information is detected.

2. The information travels through the PNS to the CNS.

3. The CNS processes the information.

4. Instructions travel through the PNS to produce a response.

The PNS is not simply located in one area of the body. It includes the network of nerves linking the CNS with regions throughout the body.

Comparing the CNS and PNS

Feature	Central nervous system	Peripheral nervous system
Abbreviation	CNS	PNS
Main components	Brain and spinal cord	Nerves outside the brain and spinal cord
Main role	Processes information and coordinates responses	Connects the CNS with the rest of the body
Relationship	Receives information and organises instructions	Carries information to and from the CNS
Further divisions required here	Brain and spinal cord	Somatic and autonomic nervous systems

A clear distinction should mention both location and function.

For example:

The CNS consists of the brain and spinal cord and processes information, whereas the PNS consists of nerves outside the CNS and carries information between the CNS and the rest of the body.

Divisions of the peripheral nervous system

The PNS has two main divisions:

1. The somatic nervous system

2. The autonomic nervous system

Both carry information between the CNS and the rest of the body, but they are involved in different types of activity.

The somatic nervous system

The somatic nervous system is the division of the PNS associated with sensory information and voluntary control of skeletal muscles.

It allows a person to:

• Receive information from sensory receptors.

• Send this information towards the CNS.

• Carry instructions from the CNS to skeletal muscles.

• Perform voluntary movements.

A voluntary movement is an action that is under conscious control.

Examples include:

• Raising a hand.

• Walking towards a door.

• Picking up a book.

• Writing an answer.

• Turning the head towards a sound.

Somatic sensory communication

The somatic nervous system carries information detected by sensory receptors towards the CNS.

For example:

1. A person sees a flashing light.

2. Sensory information is transmitted towards the CNS.

3. The brain processes the information.

4. The person consciously chooses how to respond.

This sensory communication allows the CNS to receive information about the external environment.

Somatic motor communication

The somatic nervous system also carries instructions from the CNS to skeletal muscles.

For example:

1. A person decides to lift a cup.

2. The CNS organises the movement.

3. Instructions travel through the somatic nervous system.

4. Skeletal muscles produce the movement.

The somatic nervous system therefore includes communication in both directions:

• Sensory information towards the CNS.

• Motor instructions away from the CNS.

The autonomic nervous system

The autonomic nervous system is the division of the PNS involved in regulating involuntary internal bodily processes.

An involuntary process occurs without requiring deliberate conscious control.

The autonomic nervous system contributes to the regulation of internal organs and bodily activity.

Examples of processes that do not normally require conscious control include:

• Changes in heart activity.

• Changes in breathing.

• Digestive activity.

• Internal responses to demanding situations.

The autonomic nervous system helps the body adjust automatically to changing demands.

Automatic regulation

The word autonomic refers to automatic regulation.

A person does not normally need to make a conscious decision for internal bodily processes to change.

For example:

A student is told that they must give an unexpected presentation. Their heart begins beating more quickly even though they did not consciously decide to increase it.

The change is associated with the autonomic nervous system because it involves an involuntary internal response.

The nervous and hormonal processes involved in responding to threatening situations are developed in automatic responses to danger.

Comparing the somatic and autonomic nervous systems

Feature	Somatic nervous system	Autonomic nervous system
Part of	Peripheral nervous system	Peripheral nervous system
Main focus	Sensory communication and skeletal muscles	Internal organs and bodily processes
Type of control	Mainly voluntary movement	Involuntary regulation
Example	Choosing to lift a hand	Heart activity changing automatically
Connection with CNS	Carries sensory information and motor instructions	Carries information involved in automatic internal regulation

The key difference concerns the type of body activity involved.

• Somatic: conscious interaction with the external environment and voluntary skeletal movement.

• Autonomic: automatic regulation of internal bodily functioning.

Somatic does not mean movement only

The somatic nervous system is sometimes described only as controlling voluntary movement.

This is incomplete because it also carries sensory information towards the CNS.

A complete description should include both:

• Sensory input.

• Motor output to skeletal muscles.

Autonomic does not mean uncontrolled

Autonomic processes are not random or completely uncontrolled.

They are regulated automatically rather than requiring continuous conscious decisions.

For example, a person does not consciously instruct their heart to beat once for every individual heartbeat. The activity is regulated without deliberate control.

Somatic and autonomic systems can operate together

The two divisions may contribute to the same situation.

Consider a runner waiting for a race to begin:

• Their heart activity changes automatically, involving the autonomic nervous system.

• They hear the starting signal, involving sensory communication through the somatic nervous system.

• They consciously move their legs and arms, involving somatic motor communication.

The divisions have different roles, but they are part of one coordinated nervous system.

Applying the divisions to behaviour

Consider the following scenario:

While walking to college, Ellis hears a bicycle bell behind him. He deliberately steps to the side. His heart is beating quickly because the bicycle passed very close to him.

The systems can be applied as follows:

• Information about the bell travels towards the CNS through the somatic nervous system.

• The brain processes the information as part of the central nervous system.

• Instructions to step sideways travel through the somatic nervous system to skeletal muscles.

• The automatic change in heart activity involves the autonomic nervous system.

• All communication outside the brain and spinal cord occurs through the peripheral nervous system.

A method for answering application questions

Use the following steps.

1. Identify the central processing

Look for information being processed or a response being coordinated by the brain or spinal cord.

This indicates the central nervous system.

2. Identify the communication pathway

Look for signals travelling between the CNS and the rest of the body.

This indicates the peripheral nervous system.

3. Look for conscious movement or sensory information

This usually indicates the somatic nervous system.

4. Look for automatic internal changes

This usually indicates the autonomic nervous system.

5. Apply the details

Name the specific movement, sensation or internal change from the scenario.

A strong answer would state:

The deliberate movement of Ellis’s legs involves the somatic nervous system because instructions are carried to skeletal muscles, whereas the automatic increase in heart activity involves the autonomic nervous system.

The nervous and endocrine systems

The nervous system should not be confused with the endocrine system.

Nervous system	Endocrine system
Communicates using nervous signals	Communicates using hormones
Includes the CNS and PNS	Includes glands and hormones
Somatic and autonomic systems are divisions of the PNS	Not a division of the nervous system
Carries information along neural pathways	Hormones travel through the bloodstream

The endocrine system is studied separately through glands, hormones and bodily communication.

Overall organisation of the nervous system

The complete organisation required for this lesson is:

Level	Division	Description
1	Nervous system	The body’s neural communication system
2	Central nervous system	The brain and spinal cord
2	Peripheral nervous system	Nerves outside the brain and spinal cord
3	Somatic nervous system	Sensory information and voluntary skeletal movement
3	Autonomic nervous system	Involuntary regulation of internal bodily processes

The most important relationships to remember are:

• The brain and spinal cord form the CNS.

• Nerves outside the CNS form the PNS.

• The PNS connects the CNS with the body.

• The somatic and autonomic nervous systems are divisions of the PNS.

• The somatic system is associated with sensory information and voluntary movement.

• The autonomic system regulates involuntary internal processes.

Key Words 🔑

Key word	Student-friendly definition	How it may be used in an exam
Nervous system	The communication system that transmits information and coordinates responses throughout the body.	Introduce the overall organisation of neural communication.
Central nervous system	The division of the nervous system consisting of the brain and spinal cord.	Identify where information is processed and responses are coordinated.
CNS	The abbreviation for central nervous system.	Use specialist terminology accurately in short answers.
Brain	The part of the CNS that processes information and coordinates behaviour.	Explain the central processing of information.
Spinal cord	The part of the CNS providing a communication route between the brain and the body.	Describe one component of the CNS.
Peripheral nervous system	The nerves outside the brain and spinal cord that connect the CNS with the rest of the body.	Explain how information travels to and from the CNS.
PNS	The abbreviation for peripheral nervous system.	Use specialist terminology in comparisons.
Somatic nervous system	The PNS division involved in sensory information and voluntary control of skeletal muscles.	Apply the system to conscious movement or sensory input.
Autonomic nervous system	The PNS division involved in automatic regulation of internal bodily processes.	Apply the system to involuntary internal changes.
Voluntary movement	Movement performed under conscious control.	Identify activity involving the somatic nervous system.
Involuntary process	A bodily process that does not require deliberate conscious control.	Identify activity involving the autonomic nervous system.
Sensory information	Information detected by sensory receptors and transmitted towards the CNS.	Explain one role of the somatic nervous system.
Skeletal muscle	Muscle involved in producing bodily movement.	Explain where somatic motor instructions are directed.

Common Mistakes ⚠️

Mistake: Describing the brain as part of the peripheral nervous system.

Why this is incorrect:The brain belongs to the central nervous system alongside the spinal cord.

How to improve:Remember: central means brain and spinal cord.

Mistake: Describing the spinal cord as part of the PNS.

Why this is incorrect:The spinal cord is one of the two main components of the CNS.

How to improve:Use the rule: CNS = brain + spinal cord.

Mistake: Saying the PNS is located only in the arms and legs.

Why this is incorrect:The PNS includes nerves outside the brain and spinal cord throughout the body.

How to improve:Describe it as the connection between the CNS and the rest of the body.

Mistake: Treating the somatic and autonomic nervous systems as divisions of the CNS.

Why this is incorrect:Both are divisions of the peripheral nervous system.

How to improve:Learn the hierarchy before revising individual functions.

Mistake: Describing the somatic nervous system only in terms of movement.

Why this is incorrect:It also carries sensory information towards the CNS.

How to improve:Include sensory input and voluntary motor output in your definition.

Mistake: Saying that negative or unwanted behaviour is controlled by the autonomic nervous system.

Why this is incorrect:Autonomic refers to automatic bodily regulation, not whether a behaviour is desirable.

How to improve:Look for involuntary internal processes rather than judging the behaviour.

Mistake: Assuming the autonomic nervous system controls all movement.

Why this is incorrect:Voluntary skeletal movement is primarily associated with the somatic nervous system.

How to improve:Ask whether the action was consciously chosen or involved automatic internal regulation.

Mistake: Confusing the nervous system with the endocrine system.

Why this is incorrect:The nervous system communicates through neural pathways, whereas the endocrine system uses glands and hormones.

How to improve:Keep nervous communication and hormonal communication as separate systems.

Mistake: Naming a division without applying it to the scenario.

Why this is incorrect:An application answer must explain which detail represents the system’s function.

How to improve:State both the system and the relevant sensation, movement or internal process.

Exam-Style Questions ✍️

Question 1

Which one of the following is part of the central nervous system?

A. The somatic nervous system

B. The autonomic nervous system

C. The spinal cord

D. All nerves outside the brain

[1 mark]

Question 2

Define the central nervous system.

[2 marks]

Question 3

Define the peripheral nervous system.

[2 marks]

Question 4

Distinguish between the central nervous system and the peripheral nervous system.

[4 marks]

Question 5

Explain one difference between the somatic nervous system and the autonomic nervous system.

[4 marks]

Question 6

During a lesson, Isla hears her teacher ask a question and deliberately raises her hand. Her heart is beating more quickly because she feels nervous about answering.

Using your knowledge of the nervous system, explain the roles of the somatic and autonomic nervous systems in Isla’s behaviour.

[4 marks]

Question 7

Complete the table by identifying the division of the nervous system most directly involved in each example.

Example	Division of the nervous system
Processing visual information in the brain
Carrying information between the CNS and the body
Deliberately moving the fingers to type
An automatic change in heart activity

[4 marks]

Question 8

A cyclist sees an obstacle and moves the handlebars to avoid it. At the same time, internal bodily changes occur automatically.

Explain how the central nervous system, peripheral nervous system, somatic nervous system and autonomic nervous system contribute to this situation.

[8 marks]