How does the serratus posterior inferior contribute to respiration?

The serratus posterior inferior plays a significant role in respiration, particularly in the context of forced expiration. This muscle originates from the lower thoracic and upper lumbar vertebrae and inserts into the lower ribs, specifically the 9th to 12th ribs.

During forced expiration, the serratus posterior inferior contracts to help depress the lower ribs. This action is crucial because, by pulling the ribs downwards, it aids in reducing the thoracic cavity's volume, which increases pressure in the lungs and facilitates the expulsion of air. This muscular contraction contributes to the mechanics of breathing, especially during activities requiring more vigorous respiratory effort, such as during exercise or in situations of increased respiratory demand.

Understanding this function is essential, as it emphasizes the role of the serratus posterior inferior not just in passive breathing but also in active processes that enhance respiratory efficiency.