# A person is cooking and accidentally places their hand on a hot hob. Explain how the nervous system coordinates a rapid withdrawal response, naming the neurones involved and describing how the nerve impulse passes between them.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 4.3 Nervous system and reflex action · Explain · 5 marks

> The withdrawal of the hand occurs before the person is consciously aware of the heat.

## Mark scheme (5 marks)

1. A receptor in the skin detects the heat stimulus
2. A nerve impulse is sent along a sensory neurone to the spinal cord / relay neurone
3. The impulse passes across a synapse (between neurones) using a chemical / neurotransmitter
4. A relay neurone in the spinal cord connects the sensory neurone to the motor neurone
5. The motor neurone carries the impulse to the effector (muscle), causing the hand to be withdrawn / muscle to contract

## Related

- [Revision notes for Edexcel A-Level Biology A: Salters-Nuffield (9BN0)](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/a-person-is-cooking-and-accidentally-cfc30704) · Published by Druglandscape Ltd.