Explain how a nerve impulse is transmitted from a receptor to an effector during a voluntary action, naming the types of neurones involved.

OCR GCSE Biology A: Gateway Science (J247) — B3.1 Coordination and control — the nervous system · Explain · 4 marks · View as Markdown

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

A student is sitting an exam and decides to pick up their pen to start writing. This is a voluntary action coordinated by the nervous system.

Model answer (4 marks)

A receptor in the skin detects the stimulus and generates a nerve impulse.
The impulse travels along a sensory neuron to the CNS.
Within the CNS it passes through a relay neuron.
A motor neuron carries the impulse from the relay neuron to the muscle effector, producing a response.

Examiner tips

  • Use the exact sequence: receptor → sensory neuron → CNS relay neuron → motor neuron → effector
  • Mention the types of neurons (sensory, relay, motor) as required
  • Keep answer concise to fit 4 marks

Common mistakes

  • Forgetting to name the relay neuron
  • Mixing up sensory and motor neuron roles
  • Including unnecessary detail such as synaptic transmission mechanisms

Mark scheme (4 marks)

  1. A receptor detects a stimulus and generates an impulse / signal
  2. The impulse travels along a sensory neurone to the CNS (brain and/or spinal cord)
  3. The impulse passes through a relay neurone within the CNS
  4. A motor neurone transmits the impulse from the relay neurone to the effector, which produces a response

Key terms in this question

receptor · effector

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