# A cyclist is riding along a path when a dog suddenly runs in front of them. The cyclist sees the dog and quickly squeezes the brakes. Explain how the nervous system coordinates this response, from the detection of the stimulus to the effector producing a response.

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

> The nervous system is made up of receptors, sensory neurones, relay neurones, motor neurones, and effectors. Electrical impulses travel along neurones and pass across synapses between neurones.

## Mark scheme (5 marks)

1. Receptors in the eyes detect the stimulus (the dog / light from the dog)
2. A nerve impulse travels along a sensory neurone to the central nervous system (CNS) / brain
3. The impulse passes across a synapse (between neurones) using chemicals / neurotransmitters
4. A nerve impulse travels along a motor neurone from the CNS to the effector (muscles in the hand/arm)
5. The effector (muscle) contracts / responds, causing the cyclist to squeeze the brakes

## Key terms

- [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-cyclist-is-riding-along-a-82a5af62) · Published by Druglandscape Ltd.