Which statement about the diaphragm's action is correct?

Which statement about the diaphragm's action is correct?

• A. Contracts on Inspiration
• B. Expands on Inspiration
• C. Contracts on Expiration
• D. Expands on Expiration

Answer: (A)

Breathing relies on the diaphragm as the primary inspiratory muscle. When it contracts, the diaphragm moves downward, flattening from its dome shape and increasing the vertical dimension of the thoracic cavity. This expansion of chest volume lowers intrathoracic pressure, drawing air into the lungs. Expiration, by contrast, is typically a passive process due to lung recoil when the diaphragm relaxes and moves back upward, reducing thoracic volume. So the statement that the diaphragm contracts on inspiration is the accurate description of its action.

Breathing relies on the diaphragm as the primary inspiratory muscle. When it contracts, the diaphragm moves downward, flattening from its dome shape and increasing the vertical dimension of the thoracic cavity. This expansion of chest volume lowers intrathoracic pressure, drawing air into the lungs. Expiration, by contrast, is typically a passive process due to lung recoil when the diaphragm relaxes and moves back upward, reducing thoracic volume. So the statement that the diaphragm contracts on inspiration is the accurate description of its action.