# A person is walking barefoot on a beach and steps onto a sharp shell. Nerve impulses travel rapidly along a pathway, and the person's foot is pulled away before they are consciously aware of the pain. Explain how this response is coordinated, referring to the structures involved in the reflex arc.

> Pearson Edexcel A-Level Biology A (9BI0) — 4.3 Nervous system and reflex action · Explain · 5 marks

> Reflex actions allow the body to respond rapidly to harmful stimuli without conscious thought. The pathway involved passes through the spinal cord rather than the brain.

## Mark scheme (5 marks)

1. The sharp shell acts as a stimulus, which is detected by a receptor (in the skin/foot).
2. A nerve impulse travels along a sensory neurone towards the spinal cord (coordinator/relay neurone).
3. The impulse is passed to a relay neurone (within the spinal cord), which acts as the coordinator.
4. The impulse then travels along a motor neurone to the effector (muscle in the leg/foot).
5. The effector (muscle) contracts, producing the response of pulling the foot away / the response occurs before conscious awareness because the impulse does not need to travel to the brain first.

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel A-Level Biology A (9BI0)](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-walking-barefoot-on-80f7c482) · Published by Druglandscape Ltd.