A student is sitting in a classroom when a loud noise suddenly causes them to blink. Explain how the nervous system coordinates this response, naming the types of neurones involved.

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

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

The blink response is an automatic reaction to a sudden stimulus. It involves the nervous system detecting the stimulus and sending signals to the muscles around the eye.

Model answer (5 marks)

The loud noise is detected by a sensory receptor in the ear. A sensory neuron carries the impulse to the central nervous system. In the brain the information is processed and a motor command is generated. A motor neuron carries the impulse from the CNS to the muscle around the eye. The muscle contracts, causing the eye to blink.

Examiner tips

  • Use the exact terms: sensory receptor, sensory neuron, CNS, motor neuron, effector muscle
  • Show the sequence of signal transmission
  • Mention the brain as the CNS centre
  • Keep the answer concise and to the point

Common mistakes

  • Confusing the ear with the eye as the receptor
  • Using 'nerve' instead of 'neuron'
  • Omitting the motor neuron step

Mark scheme (5 marks)

  1. The sound is detected by a receptor (in the ear / sensory receptor)
  2. A sensory neurone carries the impulse from the receptor to the central nervous system (brain or spinal cord)
  3. The central nervous system (brain) processes/coordinates the information
  4. A motor neurone carries the impulse from the CNS to the effector (muscle around the eye)
  5. The effector (muscle around the eye) contracts, causing the eye to blink

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