# Describe the pathway of a nerve impulse in a reflex arc when a person accidentally touches a sharp object with their finger. Name each type of neurone involved and state the role of each one.

> Eduqas A-Level Biology — 4.3 Variation and evolution · Describe · 5 marks

## Mark scheme (5 marks)

1. The sharp object acts as a stimulus that is detected by receptors in the finger / skin.
2. The sensory neurone carries the impulse from the receptor to the spinal cord.
3. The relay neurone (in the spinal cord / CNS) passes the impulse from the sensory neurone to the motor neurone.
4. The motor neurone carries the impulse from the spinal cord / CNS to the effector (e.g. a muscle).
5. The impulse does not travel to the brain (the response is involuntary / automatic), allowing a faster response to remove the finger from danger.

## 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-nerve-28f02998) · Published by Druglandscape Ltd.