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Question

What happens during normal expiration ?



Your Answer
A

Diaphragm contraction

Your Answer
B

Abdominal muscles contraction

Correct Answer
C

Internal intercostal muscles relaxation

Your Answer
D
Increase in volume of the thoracic cavity

Solution

The correct option is B

Internal intercostal muscles relaxation


During normal inspiration, the diaphragm and the external intercostal muscles contract. The diaphragm moves downwards increasing the volume of the thoracic cavity, and the intercostal muscles pull the ribs up expanding the rib cage and further increasing its volume. An increase in pulmonary volume decreases the intrapulmonary pressure to less than the atmospheric pressure which forces the air from outside to move into the lungs, which is inspiration. Relaxation of the diaphragm and the intercostal muscles returns the diaphragm to their normal positions and reduce the thoracic volume and thereby the pulmonary volume. This leads to an increase in intrapulmonary pressure to slightly above the atmospheric pressure causing the expulsion of air from the lungs, which is expiration. Internal intercostal muscles play a role only in forced exhalation. The question here is about normal expiration and hence, the answer is C.

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