# Explain how a reflex arc allows the body to respond rapidly to a painful stimulus, such as touching a hot surface.

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

> When a person accidentally touches a hot surface, the hand is withdrawn very quickly — often before the person is consciously aware of the pain.

## Mark scheme (4 marks)

1. A receptor detects the stimulus (heat / pain) and generates a nerve impulse
2. The nerve impulse travels along a sensory neurone to the spinal cord
3. The impulse is relayed via a relay neurone (in the spinal cord) to a motor neurone
4. The motor neurone carries the impulse to the effector (muscle), which contracts to withdraw the hand — the response does not require conscious thought from the brain, making it faster

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel International GCSE Biology (4BI1)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-a-reflex-arc-allows-d4d8edd2) · Published by Druglandscape Ltd.