What physical changes occur during inhalation?

During inhalation, the thoracic cavity expands because the diaphragm contracts and lowers, creating more space for the lungs. This increase in volume decreases the pressure within the thoracic cavity relative to the atmospheric pressure outside the body. As a result, air flows into the lungs from the environment.

The contraction of the diaphragm is crucial, as it is the primary muscle responsible for increasing the volume of the thoracic cavity during inhalation. The expansion of the thoracic cavity not only includes the diaphragm but also involves the intercostal muscles, which lift the rib cage, further enhancing the volume change.

The other options do not accurately describe the mechanics of inhalation. The diaphragm does not expand and the lungs do not contract; rather, the diaphragm's contraction leads to the expansion of the lungs. Additionally, atmospheric pressure actually remains constant rather than decreasing, and during inhalation, lung pressure is lower than atmospheric pressure, facilitating air intake. Thus, the beautiful coordination of muscle movements during this process highlights the correct understanding of inhalation dynamics.