# A doctor is testing a patient's nervous system. The doctor taps the patient's knee with a rubber hammer, and the patient's leg kicks forward automatically. This is called a reflex action. Explain how a nerve impulse travels from the receptor in the knee to the effector muscle, causing the leg to kick forward.

> OCR A-Level Biology B — Advancing Biology (H422) — 5.7 Nervous communication · Explain · 5 marks

> Reflex actions are rapid, automatic responses to stimuli that do not require conscious thought. They involve a specific pathway of neurones.

## Mark scheme (5 marks)

1. A receptor in the knee detects the stimulus (the tap)
2. A nerve impulse travels along a sensory neurone to the spinal cord (relay neurone)
3. The impulse passes across a synapse (between neurones)
4. A motor neurone carries the impulse from the spinal cord to the effector (muscle)
5. The effector muscle contracts, causing the leg to kick forward

## Key terms

- [receptor](https://www.gradenine.co.uk/glossary/receptor)
- [effector](https://www.gradenine.co.uk/glossary/effector)

## Related

- [Revision notes for OCR A-Level Biology B — Advancing Biology (H422)](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-doctor-is-testing-a-patient-s-712a5228) · Published by Druglandscape Ltd.