What effect do the internal intercostal muscles have on the ribs?

The internal intercostal muscles play a crucial role during forced expiration. When these muscles contract, they pull the ribs downward and inward, which results in the depression of the ribs. This action helps to reduce the volume of the thoracic cavity, thereby facilitating the expulsion of air from the lungs. By actively lowering the ribs, these muscles increase intrathoracic pressure, making it more efficient to push air out, especially during vigorous breathing activities. This is why the choice indicating that the internal intercostal muscles depress the ribs is correct.

In contrast, the other actions associated with the ribs, such as elevation or expansion of the thoracic cavity, are primarily functions of the external intercostal muscles and the diaphragm during inhalation rather than the internal intercostal muscles during exhalation.