# A doctor tests a patient's reflexes by tapping the tendon just below the kneecap. The lower leg kicks forward automatically. Explain how the nervous system brings about this response, naming the components involved.

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

## Mark scheme (5 marks)

1. A receptor detects the stimulus (stretch of the tendon/muscle)
2. A sensory neurone carries the impulse from the receptor to the spinal cord
3. A relay neurone in the spinal cord connects the sensory neurone to the motor neurone
4. A motor neurone carries the impulse from the spinal cord to the effector (muscle)
5. The effector (muscle in the leg) contracts, causing the lower leg to kick forward / this is a reflex arc so it does not require conscious thought from the brain

## 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-doctor-tests-a-patient-s-reflexes-5d45d9b5) · Published by Druglandscape Ltd.