# Explain how a graded receptor potential in a sensory receptor is converted into action potentials transmitted along a sensory neuron.

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

> Sensory receptors convert stimuli into electrical signals. The intensity of a stimulus is encoded in the pattern of action potentials sent to the central nervous system.

## Mark scheme (4 marks)

1. A stimulus causes ion channels in the receptor membrane to open, producing a graded (receptor) potential whose magnitude depends on stimulus intensity.
2. If the receptor potential reaches/exceeds the threshold value at the trigger zone / axon hillock, an action potential is initiated.
3. Action potentials are all-or-nothing, so stimulus intensity is encoded by the frequency of action potentials rather than their size/amplitude.
4. Action potentials propagate along the sensory neuron to the CNS by local depolarisation of adjacent membrane / saltatory conduction in myelinated neurons.

## Key terms

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

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](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/explain-how-a-graded-receptor-potential-746026be) · Published by Druglandscape Ltd.