# A young child quickly blinks when a fly suddenly moves close to their eye. This blinking response is a reflex action. Explain why reflex actions are important for survival, and describe the roles of the sensory neurone and relay neurone in producing this response.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 4.3 Nervous system and reflex action · Explain · 5 marks

> When an object moves rapidly towards the eye, the eyelid closes automatically before a person consciously decides to blink.

## Mark scheme (5 marks)

1. Reflex actions are faster than voluntary responses (so protect the body from damage / harm)
2. Reflex actions do not require conscious thought / do not involve the conscious brain
3. The sensory neurone carries the electrical impulse from the receptor (in the eye / skin) to the relay neurone (in the spinal cord)
4. The relay neurone passes the impulse through the spinal cord (CNS), connecting the sensory neurone to the motor neurone
5. Impulses pass across synapses between neurones by means of chemical transmitters (neurotransmitters diffusing across the gap)

## Key terms

- [reflex action](https://www.gradenine.co.uk/glossary/reflex-action)
- [sensory neurone](https://www.gradenine.co.uk/glossary/sensory-neurone)
- [relay neurone](https://www.gradenine.co.uk/glossary/relay-neurone)

## Related

- [Revision notes for Edexcel A-Level Biology A: Salters-Nuffield (9BN0)](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-young-child-quickly-blinks-when-46259d93) · Published by Druglandscape Ltd.