Respiratory muscle activity during inspiration and expiration

Question 1

1

Answer 1

1. Before inspiration, all respiratory muscles are relaxed.

Question 2

2

Answer 2

2. During inspiration, the diaphragm descends on contraction, increasing the vertical dimension of the thoracic cavity.

Question 3

3

Answer 3

3. Contraction of the external intercostal muscles elevates the ribs and subsequently the sternum to enlarge the thoracic cavity from front to back and from side to side.

Question 4

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Answer 4

4. During quiet passive expiration, the diaphragm relaxes, reducing the volume of the thoracic cavity from its peak inspiratory size.

Question 5

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Answer 5

5. As the external intercostal muscles relax, the elevated rib cage falls because of the force of gravity. This also reduces the volume of the thoracic cavity.

Question 6

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Answer 6

6. During active expiration, contraction of the abdominal muscles increases the intra-abdominal pressure, exerting an upward force on the diaphragm. This reduces the vertical dimension of the thoracic cavity further than it is reduced during quiet passive expiration.

Question 7

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Answer 7

7. Contraction of the internal intercostal muscles decreases the front-to-back and side-to-side dimensions by flattening the ribs and sternum.