# A person is walking barefoot on grass when they step on a sharp stone. Their foot is pulled away from the stone before they are consciously aware of any pain. Explain how the nervous system brings about this response.

> Eduqas A-Level Biology — 3.8 The nervous system · Explain · 5 marks

## Mark scheme (5 marks)

1. The sharp stone acts as a stimulus detected by a receptor (in the skin/foot)
2. A nerve impulse travels along a sensory neurone to the spinal cord
3. The impulse passes through a relay neurone (in the spinal cord)
4. A nerve impulse travels along a motor neurone to the effector (muscle in the leg/foot)
5. This is a reflex action / the response is automatic and does not involve conscious thought from the brain, which is why the foot is pulled away before the pain is felt

## 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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-person-is-walking-barefoot-on-6b2ba902) · Published by Druglandscape Ltd.