# A student states that the refractory period of a neurone is simply a time delay before the next action potential can occur. Explain why this statement is incomplete, and describe the importance of the refractory period in ensuring the correct transmission of a nerve impulse.

> OCR A-Level Biology A (H420) — 5.3 Neuronal communication · Explain · 4 marks

> During an action potential, voltage-gated sodium ion channels open, causing rapid depolarisation of the axon membrane. After this, the membrane undergoes repolarisation and a brief period during which it cannot be depolarised again, regardless of the size of the stimulus applied.

## Mark scheme (4 marks)

1. During the refractory period, voltage-gated sodium ion channels are inactivated (absolute refractory period), so the membrane cannot be depolarised again regardless of stimulus strength.
2. The refractory period ensures action potentials are discrete, separate events by preventing summation or fusion of successive impulses.
3. The refractory period enforces unidirectional transmission of the action potential along the axon, because the region behind the action potential cannot be re-excited.
4. The refractory period limits the maximum frequency of action potentials, allowing the nervous system to encode stimulus intensity as a change in impulse frequency.

## Key terms

- [refractory period](https://www.gradenine.co.uk/glossary/refractory-period)
- [action potential](https://www.gradenine.co.uk/glossary/action-potential)

## Related

- [Revision notes for OCR A-Level Biology A (H420)](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-student-states-that-the-refractory-dac7c570) · Published by Druglandscape Ltd.