GCSE Biology: Everything You Need to Know About the Human Nervous System

The nervous system is an integral part of the human body. It is one of the 11 organ systems and it is responsible for communication between our surroundings and our body, which helps us to coordinate movement and behaviour. Each GCSE Biology exam board covers the human nervous system, so this is an important topic to get your head around. 

In my 15 years as a biology teacher, I have taught hundreds of students everything they need to know about the human nervous system. Many students get bogged down in the details or think the human nervous system is just the reflex arc. You can almost guarantee a question about the nervous system will crop up in your GCSE biology paper. Hence, it is one of the key topics to focus on for revision and ensure you understand thoroughly. I am here to help you get to grips with the human nervous system for GCSE biology, so keep reading to find out more.

Introduction to the Human Nervous System

For GCSE Biology you need to know a basic definition of the nervous system: 

The human nervous system is a network of neurones connected to sense organs that communicate with our environment and induce a change in our glands or muscles. 

The function of the human nervous system is to detect changes in the external environment, such as temperature, and communicate this information to the appropriate glands or muscles within the body so that an appropriate response or action can be carried out. A pathway of nerves is used to do this and the information is transmitted via an electrical impulse along the nerves.

Components of the Nervous System

There are several components of the human nervous system including:

• Central nervous system (CNS)

  • Brain

  • Spinal cord

• Nerves and neurones

• Peripheral nervous system (PNS)

  • Somatic nervous system

  • Autonomic nervous system

Some of these you need to know about in a lot of detail. I know it can all seem rather confusing so let’s break it down into each part you need to know for GCSE biology. 

The central nervous system (CNS)

The central nervous system comprises the brain and spinal cord. The brain coordinates the response of the muscles and glands, which is where an electrical impulse carrying the ‘message’ ends up. These muscles and glands are called the effectors, as this is where the effect happens. 

Nerves and neurones

A nerve is a collection of cells called neurones. Neurones are bundled together inside one structure, which is the nerve. These can be short, like a relay neurone which travels across your spine. Or long, like the sciatic nerve which travels from the base of your spine to the big toe on your foot.

The three types of neurones you need to be aware of for GCSE Biology are:

• Sensory neurones

• Relay neurones

• Motor neurones

The three types of neurones: sensory, relay and motor

Sensory neurones

Sensory neurones are associated with sense organs which detect changes in the environment and surroundings. The sense organs are the eyes, the ears, the skin, the tongue and the nose. These contain receptor cells that detect changes, such as with temperature or chemicals, and then stimulate an electrical impulse which is sent along the sensory neurone. I always tell my students to remember that the sensory neurone does the sensing of the stimulus. See what I did there? Remember all the Ss! 

Once the impulse travels along the sensory neurone it is picked up by a relay neurone.

Relay neurones

Relay neurones are found in the brain and spinal cord. They are also called interneurons. Relay neurones tend to be shorter than other neurones as this helps speed up the impulse. They communicate the electrical impulse between a sensory neuron and a motor neurone. Where relay neurones are only used within the spinal cord and not the brain, this is called a reflex response. Don’t be confused by this: a common misconception is that relay neurones are only found in the spinal cord and not the brain. Relay neurones are indeed in the brain but when the brain is bypassed, this is an automatic response and is called a reflex. 

Relay neurones pass the electrical impulse from the sensory neurone to the motor neurone. 

Motor neurones

Motor neurones initiate the impulse from a relay neurone in the spinal cord or the brain. The impulse is transmitted along the motor neurone to an effector. Effectors are either muscles or glands and this is where the ‘effect’ or response is carried out. A response might be to move a limb away from something hot, or for a gland to release a hormone. I tell my students to remember motor neurones and movement – all the Ms. Exam questions tend to be focused on the response being to move away from a source of heat or pain so this is a good way to remember the function of motor neurones.

The peripheral nervous system

The peripheral nervous system is made up of the nerves of the rest of the body, i.e. all the nerves of the body that are not part of the brain or spinal cord. These extend from the spinal cord and brain all over the body, right down to your fingers and toes. The peripheral nervous system is responsible for transmitting impulses along the sensory neurones and back around the body in motor neurones. The relay neurones are not part of the peripheral nervous system. 

The peripheral nervous system can be divided into two parts:

• The somatic nervous system

• The autonomic nervous system

These terms are not so familiar at GCSE biology but it is good to have an understanding of the role they play in communication between different parts of the nervous system. 

The somatic nervous system

The somatic nervous system is a sub-division of the peripheral nervous system. It is responsible for communication between the sense organs and the skeletal muscles (effectors) and so controls voluntary movements. 

The autonomic nervous system

The autonomic nervous system is another part of the peripheral nervous system. It carries impulses to glands and muscles (effectors) of the internal organs and so controls involuntary movements, and therefore reflex actions. 

Reflex actions are those that we do not consciously think about. Examples include:

• Blinking

• Gag reflex

• Swallowing 

• Pain withdrawal reflex

• Knee jerk

Some of these can also be controlled consciously, such as swallowing. 

Reflex actions are rapid and automatic and so bypass the brain; this is because they can help prevent damage or pain to the body. Reflex actions can be explained by the reflex arc (see below for a diagram that shows the neurones involved and the direction of the nerve impulse). 

Functions of the Nervous System 

The function of the nervous system is to communicate information about the external environment to different parts of the body. This can be broken down into:

• Sensory function

• Motor function

You probably won’t see these terms used in exam questions for GCSE biology but for those of you hoping to study A Level Biology it is a good idea to know about them. 

Sensory function

The sensory function of the nervous system is responsible for communication between the environment, via the sense organs, and the rest of the body. This involves sensing the changes in the environment using the sense organs and their receptor cells. 

Motor function

The motor function of the nervous system is responsible for initiating a response in the effectors (glands and muscles), using the information that has been transmitted along the sensory and relay neurones to the motor neurones. 

Pathways of the Nervous System 

Reflex arc

The reflex arc is the pathway of the nervous system for an automatic reflex action. It involves an impulse transmitted from the sense organs via firstly a sensory neurone, then a relay neurone in the spinal cord (the brain is bypassed) and finally a motor neurone. (You must remember the order of the neurones in the reflex arc as this is a common exam question.) The brain is bypassed during a reflex action so that the impulse is sent rapidly to the motor neurone. No conscious thought (thinking) is involved. This would slow down the time taken for the message to be transmitted and could potentially be dangerous to the body. 

The easiest way to understand the reflex arc is with an example so let’s go through one that focuses on the pain withdrawal reflex. This is a common diagram assessed in the GCSE biology exams so make sure you can confidently label it and interpret it. Remember that the nerve impulse always starts from the stimulus. In the example below, this is the pin. You may be asked to label, with an arrow, the direction of the nerve impulse so look out for the stimulus as your starting point.

Reflex arcs are automatic and rapid; they bypass the brain

• The pin (the stimulus) is detected by a (pain/pressure/touch) receptor in the skin

• A sensory neurone sends electrical impulses to the spinal cord 

• An electrical impulse is passed to a relay neurone in the spinal cord

• A relay neurone synapses with a motor neurone

• A motor neurone carries an impulse to a muscle in the leg (the effector)

• The muscle will contract and pull the foot up and away from the sharp object (the response) when stimulated by the motor neurone

The reflex arc can be summarised as a pathway:

The reflex arc pathway

Disorders of the Nervous System 

There are several nervous system disorders. While you do not need to know about any specific nervous system disorders for GCSE biology, you may come across examples of them in exam questions where you are required to apply your knowledge of the human nervous system to information about nervous system disorders. This is more common in higher-tier papers than foundation-tier papers. 

Neurological disorders

Neurological disorders are those that affect brain function, as well as the nerves throughout the body. There are a vast number of disorders that fall into the category of neurological disorders.  Examples of neurological disorders include:

• Epilepsy

• Autism spectrum disorders

• ADHD/ADD

• Brain tumours

• Cerebral palsy

• Dementia

• Migraine 

Neurodegenerative diseases

Neurodegenerative diseases are those that occur because the nerves of the brain and body have lost function, usually over time. Examples include:

• Alzheimer's disease

• Huntington’s disease

• Parkinson’s disease

• Motor neurone disease (MND)

Understand the Nervous System and Nail Your GCSE Biology Exams

To sum up, understanding the human nervous system for GCSE biology is all about learning the key structures involved and their functions. This is required for both higher-tier papers and foundation-tier papers. 

We can summarise the key structures as:

• Sense organs – eyes, ears, nose, tongue, skin

• Neurones

  • Sensory neurones – transmit electrical impulses from sense organs to relay neurones

  • Relay neurones – transmit electrical impulses from sensory neurones to motor neurones

  • Motor neurones – transmit electrical impulses from relay neurones to the effectors (muscles and glands)

• Reflex arc – a pathway to describe and show how automatic nervous responses occur by bypassing the brain

• Effectors – muscles and glands where the response (i.e. the desired effect of the message) happens

I hope this article has helped boost your confidence in the human nervous system for GCSE biology. Take some time to review the key sections and perhaps summarise the content yourself using a mind map. Save My Exams covers all the major exam boards so take a look for free or sign up to access all our fantastic resources to support your learning and revision.