# Explain how a nerve impulse travels from a receptor to an effector during a reflex arc when a person touches a sharp object.

> WJEC A-Level Biology (Wales) — 4.2 Inheritance · Explain · 5 marks

## Mark scheme (5 marks)

1. The sharp object acts as a stimulus which is detected by receptors
2. An impulse travels along a sensory neurone to the spinal cord / CNS
3. The relay neurone carries the impulse within the spinal cord / CNS to the motor neurone
4. The impulse travels along the motor neurone to the effector (e.g. a muscle)
5. The impulse does not travel to the brain, so the response is faster / involuntary

## Key terms

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

## 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-a-nerve-impulse-travels-3aafa5df) · Published by Druglandscape Ltd.