Describe the roles of sensory neurones, the central nervous system (CNS), and motor neurones in producing a response to a stimulus.

Edexcel GCSE Biology (1BI0) — 2.3 The nervous system · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

A student accidentally touches a hot pan. Within a fraction of a second, the student pulls their hand away.

Model answer (4 marks)

A sensory neurone carries the impulse from the heat receptor to the CNS.
The CNS (brain/spinal cord) processes the signal and sends a response.
A motor neurone carries the impulse from the CNS to the muscle.
The muscle contracts, pulling the hand away.

Examiner tips

Use the exact terms: sensory neurone, CNS, motor neurone, effector.
Show the sequence: receptor → sensory neurone → CNS → motor neurone → effector.
Keep each point short and to the point.
Use UK spelling (neuron → neurone).

Common mistakes

Mixing up the direction of impulses (e.g. saying motor neurone goes to CNS).
Omitting the effector or describing it incorrectly.
Using vague language such as ‘brain’ instead of ‘CNS’.

Mark scheme (4 marks)

A sensory neurone carries nerve impulses from the receptor to the CNS (brain and/or spinal cord).
The CNS (brain and/or spinal cord) processes/coordinates the information.
A motor neurone carries nerve impulses from the CNS to the effector.
The effector (muscle/gland) produces the response, e.g. the muscle contracts to pull the hand away.

Key terms in this question

sensory neurone · central nervous system (CNS) · motor neurone