# Describe how the nervous system carries out a reflex arc when a person touches a sharp object with their finger. Include the names of the structures and neurones involved.

> Eduqas A-Level Biology — 4.2 Inheritance · Describe · 5 marks

## Mark scheme (5 marks)

1. The sharp object acts as a stimulus, detected by receptors in the finger.
2. An impulse travels along a sensory neurone to the spinal cord.
3. A relay neurone in the spinal cord passes the impulse to the motor neurone.
4. The impulse travels along the motor neurone to an effector (e.g. a muscle in the arm/hand).
5. The effector (muscle) contracts to withdraw the finger, and the response does not travel to the brain first / is involuntary.

## 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-how-the-nervous-system-carries-0a49905f) · Published by Druglandscape Ltd.