What role do internal and external intercostal muscles play during quiet respiration?

The internal and external intercostal muscles are crucial in the mechanics of breathing, particularly during quiet respiration. During this process, the external intercostal muscles primarily facilitate inhalation. They contract to elevate the ribs and expand the thoracic cavity, which decreases the pressure in the thoracic cavity compared to atmospheric pressure, allowing air to flow into the lungs.

While some might think of option B regarding the role of these muscles in “stiffening the thoracic cage,” it is more accurate to consider that these muscles contribute to the stability and mobility of the thoracic cage during respiration. The coordinated contraction of both internal and external intercostal muscles ensures that the thoracic wall moves appropriately while providing structural integrity to expand and contract effectively during breathing.

The other options do not accurately represent the specific role of intercostal muscles during quiet breathing. Increasing lung pressure typically relates to the expulsion of air rather than the action of these muscles during inhalation. Gas exchange occurs primarily in the alveoli, not through the mechanical action of the intercostal muscles themselves. While intercostal muscles are partially involved in initiating breathing, their primary function in quiet respiration is not to initiate, but to assist in the mechanics of inhalation and exhalation.