Describe how a nerve impulse travels from a receptor to an effector when a person touches a hot object and quickly pulls their hand away. Include the names of the neurones involved in your answer.

Eduqas A-Level Biology — 3.8 The nervous system · Describe · 5 marks · View as Markdown

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

Model answer (5 marks)

A receptor in the skin detects the heat and pain.
A sensory neuron carries the impulse from the receptor to the spinal cord.
A relay neuron in the spinal cord passes the impulse on.
A motor neuron carries the impulse from the spinal cord to the muscle.
The muscle contracts, pulling the hand away.

Examiner tips

  • Use the exact terms: receptor, sensory neuron, relay neuron, motor neuron, effector.
  • Show the pathway in order: receptor → sensory → relay → motor → effector.
  • Include the word "spinal cord" to satisfy the mark scheme.
  • Keep the answer short and to the point.

Mark scheme (5 marks)

  1. A receptor in the skin detects the stimulus (heat/pain)
  2. A sensory neurone carries the impulse from the receptor to the central nervous system (spinal cord / brain)
  3. A relay neurone (in the spinal cord / CNS) passes the impulse on
  4. A motor neurone carries the impulse from the CNS to the effector (muscle)
  5. The effector (muscle) responds by contracting, causing the hand to be pulled away

Key terms in this question

receptor · effector

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