# The nervous system is divided into the central nervous system (CNS) and the peripheral nervous system. Describe the roles of sensory neurones, relay neurones, and motor neurones in coordinating a response to a stimulus.

> WJEC A-Level Biology (Wales) — 3.8 The nervous system · Describe · 5 marks

> A student hears a loud bang and immediately turns their head towards the source of the sound.

## Mark scheme (5 marks)

1. Sensory neurones carry impulses from receptors to the CNS
2. Relay neurones are located in the CNS and pass impulses between sensory and motor neurones
3. Motor neurones carry impulses from the CNS to effectors
4. Effectors (muscles or glands) produce the response
5. The pathway follows the correct sequence: receptor → sensory neurone → relay neurone → motor neurone → effector

## Key terms

- [sensory neurone](https://www.gradenine.co.uk/glossary/sensory-neurone)
- [relay neurone](https://www.gradenine.co.uk/glossary/relay-neurone)
- [motor neurone](https://www.gradenine.co.uk/glossary/motor-neurone)
- [CNS](https://www.gradenine.co.uk/glossary/cns)

## Related

- [Revision notes for WJEC A-Level Biology (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" 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/the-nervous-system-is-divided-into-dad2efa2) · Published by Druglandscape Ltd.