Define the term 'synapse' and explain how a nerve impulse is transmitted across one.

WJEC GCSE Biology (Wales) — 2.5.1 The nervous system · Define and 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 synapse is a junction or gap between two neurones (or between a neurone and an effector/receptor). When a nerve impulse reaches the presynaptic terminal, it triggers the release of a neurotransmitter. The neurotransmitter diffuses across the synaptic gap and binds to receptors on the postsynaptic neurone, generating a new nerve impulse.

Examiner tips

Use the exact definition of a synapse; include the gap and the two cells involved.
Explain the sequence: impulse arrival → neurotransmitter release → diffusion → receptor binding → new impulse.
Show the chemical nature of the signal (neurotransmitter).
Use the term 'postsynaptic' correctly.

Common mistakes

Confusing the synapse with the axon hillock or dendrite.
Failing to mention the neurotransmitter or the postsynaptic receptor.
Using vague terms like 'signal' instead of 'neurotransmitter'.

Mark scheme (4 marks)

A synapse is a junction/gap between two neurones (or between a neurone and an effector/receptor)
A nerve impulse arriving at the synapse causes the release of a chemical (neurotransmitter) from the presynaptic neurone
The neurotransmitter diffuses across the synaptic gap
The neurotransmitter binds to receptors on the postsynaptic neurone, generating a new nerve impulse

Key terms in this question

synapse · nerve impulse