# Explain how the nervous system and the cardiovascular system work together to maintain adequate oxygen delivery to skeletal muscle during vigorous exercise.

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

> During vigorous exercise, skeletal muscle cells consume oxygen at a rate that can be up to 20 times greater than at rest. The body must rapidly adjust several physiological parameters to meet this increased demand.

## Mark scheme (4 marks)

1. The nervous system detects increased muscular activity / increased CO₂ or decreased O₂ levels via chemoreceptors or proprioceptors and sends nerve impulses to the cardiovascular centre in the medulla oblongata.
2. Nerve impulses from the cardiovascular centre travel via the sympathetic nervous system to the sinoatrial node, increasing heart rate (and stroke volume / cardiac output).
3. Sympathetic nerve impulses also cause vasodilation of arterioles supplying skeletal muscle, increasing blood flow and oxygen delivery to those muscles.
4. The increased cardiac output combined with vasodilation ensures greater oxygen delivery to respiring muscle cells, maintaining aerobic respiration and removing CO₂ / metabolic waste products.

## 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)
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