When breathing in, what happens first according to physiological principles?

While the chosen answer suggests that the chest expands first, the correct sequence of events during inhalation actually begins with the contraction of the diaphragm. When the diaphragm contracts, it moves downward, increasing the volume of the thoracic cavity. This reduction in pressure within the cavity allows air to flow into the lungs, leading to lung inflation as a subsequent step. The expansion of the chest wall occurs as a result of the change in thoracic volume and the negative pressure created.

This sequence highlights the importance of the diaphragm as the primary muscle of respiration, effectively initiating the process of breathing. Therefore, understanding the roles of the diaphragm and the mechanics of thoracic cavity expansion is crucial for grasping the physiological principles of ventilation.