# Describe the roles of the sensory neurone, relay neurone and motor neurone in carrying a nerve impulse during a reflex action.

> Pearson Edexcel International GCSE Biology (4BI1) — 2.15 Coordination and response: humans · Describe · 4 marks

> A student accidentally touches a very cold surface and rapidly withdraws their hand before they are consciously aware of the cold sensation.

## Mark scheme (4 marks)

1. The sensory neurone carries the impulse from the receptor to the spinal cord / relay neurone
2. The relay neurone passes the impulse within the spinal cord / between the sensory and motor neurones
3. The motor neurone carries the impulse from the spinal cord / relay neurone to the effector / muscle
4. The impulse passes across synapses between neurones / the pathway does not pass through the conscious brain (allowing a rapid response)

## Key terms

- [sensory neurone](https://www.gradenine.co.uk/glossary/sensory-neurone)
- [relay neurone](https://www.gradenine.co.uk/glossary/relay-neurone)
- [motor neurone](https://www.gradenine.co.uk/glossary/motor-neurone)
- [reflex action](https://www.gradenine.co.uk/glossary/reflex-action)

## Related

- [Revision notes for Pearson Edexcel International GCSE Biology (4BI1)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" 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/describe-the-roles-of-the-sensory-0509a409) · Published by Druglandscape Ltd.