# Explain how the nervous system carries out a reflex arc when a person touches a sharp object. Include the names of the neurones involved and the role of the effector in your answer.

> WJEC A-Level Biology (Wales) — 4.3 Variation and evolution · Explain · 5 marks

## Mark scheme (5 marks)

1. The sharp object acts as a stimulus and is detected by receptors (in the skin)
2. An impulse travels along the sensory neurone to the spinal cord
3. The relay neurone in the spinal cord passes the impulse to the motor neurone
4. The impulse travels along the motor neurone to the effector (a muscle)
5. The effector (muscle) contracts/responds to remove the hand from the sharp object / the reflex does not involve the brain so the response is faster

## Key terms

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

## 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)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-nervous-system-carries-1d42c5b2) · Published by Druglandscape Ltd.