# Explain how the respiratory system and the musculoskeletal system are integrated to allow a person to breathe in during inhalation.

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

## Mark scheme (4 marks)

1. The nervous system sends motor nerve impulses to the respiratory muscles (diaphragm and/or intercostal muscles), stimulating them to contract.
2. Contraction of the diaphragm (moves downward / flattens) and/or external intercostal muscles (ribs move up and out) increases the volume of the thoracic cavity.
3. Increased thoracic volume causes a decrease in air pressure inside the lungs (below atmospheric pressure).
4. Air flows into the lungs down the pressure gradient (from high atmospheric pressure to lower lung pressure), achieving inhalation.

## Key terms

- [inhalation](https://www.gradenine.co.uk/glossary/inhalation)

## 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-the-respiratory-system-and-413518ee) · Published by Druglandscape Ltd.