Cooper Krone Exam 1 Practice

Which action does the serratus posterior inferior perform?

Elevates the ribs Depresses the ribs Protracts the scapula Rotates the head

Correct Answer:

Depresses the ribs

Explanation:

In breathing, muscles can raise or lower the ribs. The serratus posterior inferior specifically depresses the lower ribs, aiding expiration. It runs from the lower thoracic and upper lumbar spine to the inferior borders of ribs 9–12, so when it contracts it pulls those ribs downward, reducing thoracic volume during forced breathing. It doesn’t elevate ribs (that’s the serratus posterior superior), it doesn’t move the scapula (that’s serratus anterior), and it doesn’t rotate the head. So its action is to depress the ribs.

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