# A student is investigating how muscles contract. Explain how a muscle contracts when a nerve impulse arrives at the neuromuscular junction, including the role of ATP in this process.

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

> Muscles are made up of muscle fibres that contain protein filaments. When stimulated, these filaments slide past each other to shorten the muscle. This process requires energy from respiration.

## Mark scheme (5 marks)

1. A nerve impulse triggers the release of a neurotransmitter at the neuromuscular junction
2. The neurotransmitter binds to receptors on the muscle fibre, causing the muscle fibre to be stimulated
3. Protein filaments (actin and myosin) slide past each other, causing the muscle fibre to shorten / contract
4. ATP provides the energy needed for the filaments to slide / for muscle contraction
5. ATP is produced by aerobic respiration (in mitochondria) using glucose and oxygen

## Key terms

- [neuromuscular junction](https://www.gradenine.co.uk/glossary/neuromuscular-junction)
- [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/a-student-is-investigating-how-muscles-9801a2e0) · Published by Druglandscape Ltd.