Explain how a synapse allows a nerve impulse to pass 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)

A nerve impulse reaches the end of the pre‑synaptic neuron, the synaptic knob.
Neurotransmitter is released into the synaptic cleft.
It diffuses across the cleft and binds to receptors on the post‑synaptic membrane.
This binding generates a new nerve impulse in the post‑synaptic neuron.

Examiner tips

Use the exact sequence of events; mention the synaptic knob, neurotransmitter release, diffusion, receptor binding and new impulse.
Show the direction of the signal – from pre‑ to post‑synaptic neuron.
Use the term "synaptic cleft" and "neurotransmitter" to gain full marks.

Common mistakes

Confusing the pre‑ and post‑synaptic neuron; writing that the impulse starts in the post‑synaptic neuron.
Omitting the synaptic cleft or the receptor binding step.
Using vague terms like "signal" instead of "nerve impulse" or "neurotransmitter".

Mark scheme (4 marks)

A nerve impulse arrives at the end of the first (pre-synaptic) neurone / synaptic knob
Neurotransmitter is released into the synaptic gap / cleft
Neurotransmitter diffuses across the synaptic gap and binds to receptors on the post-synaptic membrane
A new nerve impulse is generated in the post-synaptic neurone

Key terms in this question

synapse · neurone · nerve impulse