What role does the diaphragm play during inhalation?

The diaphragm plays a crucial role during the process of inhalation by contracting, which leads to a decrease in pressure within the thoracic cavity. When the diaphragm contracts, it moves downward, increasing the volume of the chest cavity. This expansion creates a pressure differential between the inside of the thoracic cavity and the atmospheric pressure outside the body. As a result, air flows into the lungs as they follow the path of least resistance, moving from an area of higher pressure (the atmosphere) to an area of lower pressure (the lungs).

Understanding this mechanism is essential, as it highlights the diaphragm's function as the primary muscle of respiration, actively working to facilitate breathing. When considering the other options, relaxing the diaphragm would increase pressure rather than decrease it, remaining still would not create airflow, and expansion does not describe the diaphragm’s action during inhalation accurately.

Thus, the correct answer emphasizes the diaphragm’s contraction and its vital role in enabling the flow of air into the lungs during inhalation.