Describe how the nervous system coordinates a response when a person touches a very hot object. In your answer, name the type of neurones involved and the role of the central nervous system (CNS).

OCR GCSE Biology A: Gateway Science (J247) — B3.1 Coordination and control — 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 is cooking and accidentally places their hand on a hot hob. Their hand is pulled away before they are even consciously aware of the pain.

Model answer (4 marks)

Receptor in the skin detects the heat and pain and generates a nerve impulse.
Sensory neurone carries the impulse to the spinal cord.
A relay neurone in the spinal cord passes the impulse to a motor neurone.
Motor neurone carries the impulse to the muscle, causing the hand to withdraw.

Examiner tips

  • Use the exact sequence: receptor → sensory neurone → relay neurone → motor neurone → effector.
  • Mention the CNS (spinal cord) as the site of the relay.
  • Show the type of neurones (sensory, relay, motor).

Common mistakes

  • Confusing the relay neurone with the motor neurone.
  • Omitting the role of the spinal cord as part of the CNS.
  • Using vague terms like "nerve cells" instead of specific neurone types.

Mark scheme (4 marks)

  1. Receptor detects the stimulus (heat/pain) and generates a nerve impulse
  2. Sensory neurone carries the impulse to the CNS (spinal cord)
  3. Relay neurone in the CNS passes the impulse to the motor neurone
  4. Motor neurone carries impulse to the effector (muscle) which produces the response (hand is withdrawn)

Key terms in this question

central nervous system (CNS)

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