A girl runs hard for a minute and then stops…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A girl runs hard for a minute and then stops. For some time she breathes fast and deep.
- What does her muscle make in large amounts, and what happens to its level in the blood?
- Which parts of the nervous system sense the change?
- Which part sends the signals to the diaphragm and the intercostal muscles?
- What happens to the carbon dioxide level once she has breathed hard for a while, and why?
Need a reminder? The key ideaShow
The respiratory rhythm centre is in the medulla. The pneumotaxic centre in the pons can shorten inspiration. The chemosensitive area next to the rhythm centre, and receptors in the aortic arch and the carotid artery, sense carbon dioxide and hydrogen ions. The role of oxygen is insignificant.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) The muscles make more carbon dioxide, so its level in the blood, and the level of hydrogen ions, rises.
Step 2. (b) The chemosensitive area of the brain, and the receptors of the aortic arch and the carotid artery, sense the change.
Step 3. (c) The respiratory rhythm centre of the medulla sends the signals.
Step 4. (d) The level falls back, because the fast, deep breathing removes more carbon dioxide from the blood. This is a feedback loop.
Answer: (a) more carbon dioxide, so its level rises; (b) the chemosensitive area and the receptors; (c) the rhythm centre; (d) it falls back, because breathing removes it.
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