# Explain how the refractory period of a neuron limits the direction and frequency of action potential propagation.

> IB DP Biology Standard Level (2023 syllabus) — C2.2 Neural signalling · Explain · 4 marks

## Mark scheme (4 marks)

1. During the refractory period, voltage-gated sodium channels are inactivated (or closed and unable to open), so a new action potential cannot be generated in that region.
2. This prevents the action potential from travelling backwards (in the direction it came from), ensuring unidirectional propagation along the axon.
3. Because no new action potential can begin until the refractory period is over, there is a minimum time interval between successive action potentials, limiting the maximum frequency of firing.
4. Stronger stimuli can increase firing frequency only up to this maximum set by the refractory period, which is how stimulus intensity is coded (rate coding) rather than by changing the size of individual action potentials (all-or-nothing principle).

## Key terms

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

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-refractory-period-of-c6a6bfa6) · Published by Druglandscape Ltd.