# Explain how the sliding filament model accounts for muscle contraction, including the roles of actin, myosin and ATP in this process.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 4.2 Muscle contraction · Explain · 5 marks

> Skeletal muscles are made up of muscle fibres containing two types of protein filaments — actin and myosin. When a muscle contracts, these filaments slide past one another, shortening the muscle.

## Mark scheme (5 marks)

1. Myosin heads attach to actin filaments, forming cross-bridges
2. Myosin heads pivot / pull actin filaments towards the centre of the sarcomere
3. ATP provides the energy needed for the myosin head to detach from actin
4. ATP is hydrolysed to ADP + Pi, releasing energy to re-cock / reset the myosin head
5. Repeated attachment–pivot–detachment cycles cause actin filaments to slide, shortening the overall muscle / sarcomere

## Key terms

- [actin](https://www.gradenine.co.uk/glossary/actin)
- [myosin](https://www.gradenine.co.uk/glossary/myosin)
- [sliding filament model](https://www.gradenine.co.uk/glossary/sliding-filament-model)
- [ATP](https://www.gradenine.co.uk/glossary/atp)

## 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/explain-how-the-sliding-filament-model-01e280ab) · Published by Druglandscape Ltd.