# Describe the pathway of a reflex arc when a person steps on a sharp object. Include the role of each type of neurone involved.

> Eduqas A-Level Biology — 4.4 Application of reproduction and genetics · Describe · 5 marks

> When a person accidentally steps on a sharp object, they quickly pull their foot away before they are fully aware of the pain.

## Mark scheme (5 marks)

1. The sharp object acts as a stimulus which is detected by receptors in the skin / foot
2. A nerve impulse travels along the sensory neurone to the spinal cord (CNS)
3. The relay neurone in the spinal cord / CNS passes the impulse to the motor neurone
4. The motor neurone carries the impulse from the spinal cord / CNS to an effector (muscle in the leg / foot)
5. The impulse does not travel to the brain / the response is involuntary, so the foot is pulled away before conscious awareness

## Key terms

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

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Source: [GradeNine](https://www.gradenine.co.uk/q/describe-the-pathway-of-a-reflex-bc7c88fe) · Published by Druglandscape Ltd.