# Explain how the nervous system and the musculoskeletal system are integrated to allow a skeletal muscle to contract in response to a voluntary stimulus.

> IB DP Biology Standard Level (2023 syllabus) — C3.1 Integration of body systems · Explain · 4 marks

## Mark scheme (4 marks)

1. A motor neurone carries an action potential / nerve impulse from the central nervous system (brain or spinal cord) to the skeletal muscle.
2. At the neuromuscular junction, the action potential triggers release of acetylcholine (a neurotransmitter) into the synaptic cleft.
3. Acetylcholine binds to receptors on the muscle cell membrane (motor end plate / sarcolemma), generating a new action potential in the muscle fibre.
4. The action potential in the muscle fibre leads to muscle contraction, involving the interaction of actin and myosin filaments (sliding filament mechanism) so that the muscle shortens and moves the skeleton.

## 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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-nervous-system-and-0cb489a6) · Published by Druglandscape Ltd.