Explain what happens at a synapse to allow a nerve impulse to continue from one neurone to the next.

Eduqas GCSE Biology — 2.5.1 The nervous system · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

The action potential reaches the axon terminal and causes voltage‑gated
Ca²⁺ channels to open. The influx of Ca²⁺ triggers vesicles containing
neurotransmitter to fuse with the presynaptic membrane and release their
contents into the synaptic cleft. The neurotransmitter then diffuses across
the cleft and binds to specific receptors on the postsynaptic membrane.
Binding opens ion channels, allowing ions to flow and generating a new
action potential in the postsynaptic neuron.

Examiner tips

  • Use the sequence: action potential → Ca²⁺ influx → vesicle fusion → neurotransmitter release → diffusion → receptor binding → postsynaptic potential
  • Mention the role of voltage‑gated Ca²⁺ channels and ion flow to show understanding
  • Keep the answer concise and use correct terminology

Common mistakes

  • Confusing the presynaptic and postsynaptic neuron, or omitting the Ca²⁺ step
  • Using vague terms like ‘signal’ instead of ‘neurotransmitter’
  • Leaving out the diffusion step or the generation of a new action potential

Mark scheme (4 marks)

  1. The nerve impulse causes vesicles containing neurotransmitter to move to / fuse with the presynaptic membrane
  2. Neurotransmitter diffuses across the synaptic cleft
  3. Neurotransmitter binds to receptors on the postsynaptic membrane
  4. This generates / triggers a new nerve impulse in the postsynaptic neurone

Key terms in this question

synapse

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