Which muscle depresses the ribs during respiration?

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Multiple Choice

Which muscle depresses the ribs during respiration?

Explanation:
During expiration, some back muscles help reduce the rib cage by pulling the lower ribs downward. Serratus posterior inferior does exactly this: its fibers run to the inferior borders of the lower ribs (9–12) and, when it contracts, pulls those ribs downward and slightly inward. This action lowers the thoracic volume to assist in expelling air. The other muscles listed don’t primarily depress the ribs. Splenius capitis mainly moves and rotates the head and neck. Serratus anterior protracts the scapula on the chest wall. Latissimus dorsi powers movements of the arm and supports the back, but it isn’t a primary rib-depressing muscle during respiration.

During expiration, some back muscles help reduce the rib cage by pulling the lower ribs downward. Serratus posterior inferior does exactly this: its fibers run to the inferior borders of the lower ribs (9–12) and, when it contracts, pulls those ribs downward and slightly inward. This action lowers the thoracic volume to assist in expelling air.

The other muscles listed don’t primarily depress the ribs. Splenius capitis mainly moves and rotates the head and neck. Serratus anterior protracts the scapula on the chest wall. Latissimus dorsi powers movements of the arm and supports the back, but it isn’t a primary rib-depressing muscle during respiration.

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