# Explain how a nerve impulse travels from a sensory neurone to a motor neurone across a synapse, and describe one structural adaptation of a neurone that allows nerve impulses to travel quickly.

> WJEC A-Level Biology (Wales) — 4.4 Application of reproduction and genetics · Explain · 5 marks

## Mark scheme (5 marks)

1. When an impulse arrives at the presynaptic neurone, a neurotransmitter is released into the synaptic cleft
2. The neurotransmitter diffuses across the synaptic cleft
3. The neurotransmitter binds to receptors on the postsynaptic neurone
4. This triggers a new nerve impulse in the postsynaptic neurone
5. One structural adaptation named and correctly linked to speed — e.g. the axon has a myelin sheath which provides electrical insulation and speeds up the impulse; OR the axon is long so the impulse travels over large distances without crossing a synapse (which would slow it down); OR dendrites pick up impulses from other neurones (allowing rapid reception)

## Key terms

- [synapse](https://www.gradenine.co.uk/glossary/synapse)

## Related

- [Revision notes for WJEC A-Level Biology (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-a-nerve-impulse-travels-f99ad16c) · Published by Druglandscape Ltd.