What is the function of the internal intercostal muscles during expiration?

The internal intercostal muscles play a vital role in the respiratory process, particularly during expiration. Their primary function during this phase of breathing is to assist in decreasing the volume of the thoracic cavity.

When these muscles contract, they pull the rib cage downward and inward, which reduces the space within the thoracic cavity. This decrease in volume leads to an increase in pressure in the lungs, causing air to be pushed out of the respiratory system. The action of the internal intercostals is crucial for forced expiration, such as during vigorous activities or in situations requiring increased respiratory effort.

In contrast, other functions, such as increasing the volume of the thoracic cavity, are primarily supported by the external intercostal muscles and diaphragm during inhalation. While stabilizing the rib cage and maintaining posture are important functions in a broader context of muscle action, they are not specifically the direct role of the internal intercostal muscles during expiration.