Explain the role of neurotransmitters in transmitting a nerve impulse across a synapse.

Edexcel GCSE Biology (1BI0) — 2.3 The nervous system · Explain · 4 marks · View as Markdown

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

When a nerve impulse reaches the end of one neurone, it cannot jump directly to the next neurone. Instead, a chemical process takes place at the junction between the two neurones.

Model answer (4 marks)

A nerve impulse arriving at the synapse causes neurotransmitters to be released from the presynaptic neurone’s synaptic knob into the synaptic cleft.
Neurotransmitters diffuse across the synaptic cleft.
They bind to receptors on the postsynaptic neurone.
Binding of neurotransmitters generates a new nerve impulse in the postsynaptic neurone.

Examiner tips

Use the exact sequence of release, diffusion, binding and impulse generation.
Show the role of the presynaptic knob and synaptic cleft.
Mention receptors on the postsynaptic side.
Keep the answer concise and use correct terminology.

Common mistakes

Confusing the presynaptic and postsynaptic neurone.
Omitting the synaptic cleft or receptors.
Using vague terms like ‘signal’ instead of ‘neurotransmitter’ or ‘nerve impulse’.

Mark scheme (4 marks)

A nerve impulse arriving at the synapse causes neurotransmitters to be released (from the presynaptic neurone / synaptic knob / synaptic vesicles)
Neurotransmitters diffuse across the synaptic cleft (gap between the two neurones)
Neurotransmitters bind to receptors on the postsynaptic (next) neurone
Binding of neurotransmitters generates / triggers a new nerve impulse in the postsynaptic neurone

Key terms in this question

neurotransmitters · synapse · nerve impulse