# Explain how a simple reflex arc allows the body to respond rapidly to a harmful stimulus. Include the sequence of structures involved in the reflex arc in your answer.

> AQA A-Level Biology (7402) — 3.6.1 Stimuli and Responses · Explain · 5 marks

> A person accidentally touches a very hot surface and quickly pulls their hand away before they are consciously aware of the pain.

## Mark scheme (5 marks)

1. A receptor detects the stimulus (heat/pain) and generates a nerve impulse
2. The impulse travels along a sensory neurone to the spinal cord / relay neurone
3. The relay neurone (in the spinal cord) passes the impulse to the motor neurone
4. The impulse travels along a motor neurone to the effector (muscle)
5. The response is rapid / does not involve conscious thought because the impulse does not travel to the brain (bypasses the brain / is processed in the spinal cord)

## Key terms

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

## Related

- [Revision notes for AQA A-Level Biology (7402)](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)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-a-simple-reflex-arc-640d5014) · Published by Druglandscape Ltd.