Which muscle is most important for quiet inspiration?

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Multiple Choice

Which muscle is most important for quiet inspiration?

Quiet inspiration is driven mainly by the diaphragm. When the diaphragm contracts, it flattens and moves downward, increasing the vertical size of the thoracic cavity. This expansion lowers intrathoracic pressure relative to the air outside, so air flows into the lungs to fill the tidal volume. The external intercostal muscles aid by lifting the rib cage a bit, but they are secondary during quiet breathing. Abdominal muscles are primarily involved in expiration (especially forced expiration and coughing) and would oppose inspiration if they contracted. The pectoralis major can assist only in deep or labored breathing by lifting the sternum, but it isn’t needed for quiet breathing. Thus, the diaphragm is the most important muscle for quiet inspiration.

Quiet inspiration is driven mainly by the diaphragm. When the diaphragm contracts, it flattens and moves downward, increasing the vertical size of the thoracic cavity. This expansion lowers intrathoracic pressure relative to the air outside, so air flows into the lungs to fill the tidal volume. The external intercostal muscles aid by lifting the rib cage a bit, but they are secondary during quiet breathing. Abdominal muscles are primarily involved in expiration (especially forced expiration and coughing) and would oppose inspiration if they contracted. The pectoralis major can assist only in deep or labored breathing by lifting the sternum, but it isn’t needed for quiet breathing. Thus, the diaphragm is the most important muscle for quiet inspiration.

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