10.2 The Structure and Function of the Human Nervous System

A free GCSE Biology lesson for AQA (8461) from OBA School: receptors, the central nervous system, neurones and how information passes through the body. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

• Describe the function of the nervous system and the pathway from stimulus to response
• Name the parts of the central nervous system
• Match sense organs to the stimuli their receptors detect
• Describe how the structure of a neurone is adapted to its function

Key words

• Stimulus: A change in the environment (inside or outside the body) that can be detected.
• Receptor: A cell that detects a stimulus and turns it into electrical impulses.
• Neurone: A nerve cell. It carries electrical impulses.
• Nerve: A bundle of many neurone axons wrapped together.
• CNS: The central nervous system: the brain and spinal cord.
• Impulse: An electrical signal that travels along a neurone.

What the nervous system does

The nervous system lets you react to your surroundings and coordinate your behaviour. Information from receptors passes along neurones as electrical impulses to the central nervous system (CNS). The CNS is a coordination centre: it receives information and sends impulses to effectors.

Worked example: catching a ball

Stimulus: the ball coming towards you. Receptors: light receptors in the retina of the eye.
Impulses travel along sensory neurones to the brain, which decides what to do.
Impulses travel along motor neurones to the arm muscles (effectors), which contract to catch the ball.

Answer: Eye → sensory neurone → brain → motor neurone → arm muscles

Receptors and sense organs

Receptors are often grouped in sense organs. Each type is sensitive to one kind of stimulus.

• Eye; Receptors detect Light (intensity and colour)
• Ear; Receptors detect Sound; also changes in position (balance)
• Nose; Receptors detect Chemicals in the air (smell)
• Tongue; Receptors detect Chemicals in food and drink (taste)
• Skin; Receptors detect Touch, pressure, pain and temperature changes

Exam tip: the stimulus for the nose and tongue is “chemicals”, not “smell” or “taste”. Smell and taste are what the brain makes of the information.

Neurones

There are three types: sensory neurones carry impulses from receptors to the CNS; relay neurones (in the CNS) carry them from sensory to motor neurones; motor neurones carry them from the CNS to effectors.

• Long axon; Adaptation Carries impulses a long way, e.g. from the spinal cord to the foot (up to about 1 m).
• Dendrites; Adaptation Many branches connect with lots of other neurones to receive impulses.
• Myelin sheath; Adaptation Fatty layer that insulates the axon and speeds up the impulse.
• Nerve endings; Adaptation Pass the impulse on to other neurones or effectors at synapses.

Worked example: speed of an impulse

An impulse travels 0.90 m along a motor neurone in 0.0075 s. Calculate its speed.
speed = distance ÷ time = 0.90 ÷ 0.0075 = 120 m/s.

Answer: 120 m/s

Common mistakes

• Calling a neurone a “nerve”. A nerve is a bundle of many neurones.
• Saying the brain is the whole CNS. The CNS is the brain and spinal cord.
• Saying the stimulus for the eye is “seeing”. The stimulus is light.
• Mixing up sensory and motor neurones. Sensory carry impulses to the CNS; motor carry them away to effectors.

Revision questions

Try these, then check your answers below each one.

Question 1. What makes up the central nervous system (CNS)? (Choose from: The brain and sense organs, The brain only, The brain and spinal cord, All the nerves in the body.)

Answer: The brain and spinal cord

Working: The CNS is the brain and spinal cord.

Question 2. Which shows the correct order of a nervous response? (Choose from: stimulus → receptor → sensory neurone → CNS → motor neurone → effector → response, stimulus → sensory neurone → receptor → CNS → effector → motor neurone → response, receptor → stimulus → CNS → sensory neurone → motor neurone → response → effector, stimulus → receptor → motor neurone → CNS → sensory neurone → effector → response.)

Answer: stimulus → receptor → sensory neurone → CNS → motor neurone → effector → response

Working: Receptors detect the stimulus, sensory neurones carry impulses to the CNS, motor neurones carry them to the effector.

Question 3. What is the name of the fatty layer that insulates an axon and speeds up impulses? (two words)

Answer: myelin sheath

Working: The myelin sheath insulates the axon and speeds up impulses.

Related lessons

• Previous lesson: 10.1 Principles of Homeostasis
• Next lesson: 10.3 Reflex Actions
• In this chapter: 10.4 The Brain
• In this chapter: 10.5 The Eye
• In this chapter: 10.6 Common Problems of the Eye

Continue in the full course

This lesson is section 10.2 (AGCBH1002) of our free GCSE Biology course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Biology course.