What allows the thoracic cavity to expand during inhalation?

The expansion of the thoracic cavity during inhalation is primarily due to the contraction of the diaphragm. When the diaphragm contracts, it moves downward, increasing the volume of the thoracic cavity. This change in volume causes a decrease in pressure within the cavity compared to the atmospheric pressure outside the body, leading to air being drawn into the lungs. The diaphragm plays a crucial role as the main muscle involved in respiration, and its movement directly facilitates the inhalation process.

The intercostal muscles, which are involved in expanding and contracting the rib cage, do not relax during inhalation; instead, they often contract to assist the diaphragm in raising the ribs further, aiding in the overall increase in thoracic volume. The adaptation of rib shape and the elasticity of lung tissue are important for overall pulmonary function, but they do not directly contribute to the expansion mechanism during inhalation the way the contraction of the diaphragm does. Hence, the diaphragm is key to initiating inhalation effectively.