# Explain what happens in a reflex arc when a person accidentally touches a sharp object with their finger. Your answer should include the roles of receptors, sensory neurones, relay neurones, motor neurones and effectors.

> Eduqas A-Level Biology — 4.6 The nervous system · Explain · 5 marks

## Mark scheme (5 marks)

1. Receptors in the finger detect the stimulus (sharp object / pain)
2. A nerve 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 (muscle)
5. The reflex is involuntary / the impulse does not travel to the brain, so the response is faster

## Key terms

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

## Related

- [Revision notes for Eduqas A-Level Biology](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-what-happens-in-a-reflex-ae6c325c) · Published by Druglandscape Ltd.