# Explain why the refractory period is essential for the transmission of nerve impulses along a neurone.

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

> When a nerve impulse travels along a myelinated motor neurone, each region of the axon membrane undergoes a sequence of permeability changes. For a brief period after depolarisation, the membrane cannot be depolarised again, regardless of the strength of the stimulus applied.

## Mark scheme (4 marks)

1. The refractory period ensures impulses travel in one direction only
2. The membrane cannot be re-depolarised during the refractory period because sodium ion channels are inactivated / closed
3. The refractory period limits the maximum frequency of impulses
4. This means impulse frequency (rather than amplitude) codes for stimulus intensity

## Key terms

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

## Related

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-the-refractory-period-is-b6a25e77) · Published by Druglandscape Ltd.