Explain how the nervous system and the cardiovascular system work together to maintain adequate oxygen delivery to skeletal muscle during vigorous exercise.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
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.
Model answer (4 marks)
The nervous system senses the rise in muscular activity and the accompanying fall in O₂ / rise in CO₂ through proprioceptors and chemoreceptors, and transmits this information to the cardiovascular centre in the medulla oblongata.
The cardiovascular centre sends sympathetic nerve impulses to the heart. These impulses reach the sinoatrial node, increasing heart rate and, via the sympathetic stimulation of the atrioventricular node and ventricular myocardium, increasing stroke volume. The combined effect raises cardiac output.
Sympathetic activity also causes vasodilation of the arterioles that supply skeletal muscle, thereby reducing peripheral resistance and directing more blood toward the active muscles.
The simultaneous increase in cardiac output and muscle blood flow ensures that oxygen delivery matches the heightened demand, allowing aerobic respiration to continue and CO₂ and other waste products to be removed efficiently.
The cardiovascular centre sends sympathetic nerve impulses to the heart. These impulses reach the sinoatrial node, increasing heart rate and, via the sympathetic stimulation of the atrioventricular node and ventricular myocardium, increasing stroke volume. The combined effect raises cardiac output.
Sympathetic activity also causes vasodilation of the arterioles that supply skeletal muscle, thereby reducing peripheral resistance and directing more blood toward the active muscles.
The simultaneous increase in cardiac output and muscle blood flow ensures that oxygen delivery matches the heightened demand, allowing aerobic respiration to continue and CO₂ and other waste products to be removed efficiently.
Examiner tips
- Use the word ‘sympathetic’ to link nervous and cardiovascular actions; mention both heart rate and stroke volume; include vasodilation of muscle arterioles; explain the final effect on oxygen delivery.
Common mistakes
- Confusing parasympathetic with sympathetic actions; omitting the role of chemoreceptors; failing to mention increased cardiac output or vasodilation; writing in passive voice or vague terms.
Mark scheme (4 marks)
- 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.
- Nerve impulses from the cardiovascular centre travel via the sympathetic nervous system to the sinoatrial node, increasing heart rate (and stroke volume / cardiac output).
- Sympathetic nerve impulses also cause vasodilation of arterioles supplying skeletal muscle, increasing blood flow and oxygen delivery to those muscles.
- 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
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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