Final answer:
During inhalation, the diaphragm contracts and moves downward while the chest wall expands outward. In contrast, during exhalation, the diaphragm relaxes and moves upward as the chest wall contracts inward.
Step-by-step explanation:
When we discuss the expansion of the chest wall, we are referring to the act of inhalation where the diaphragm moves downward and the chest wall moves outward. This movement decreases the pressure in the thoracic cavity relative to the outside environment, causing air to flow into the lungs. When exhaling, the diaphragm relaxes, moving upward, and the chest wall moves inward, increasing the thoracic pressure and forcing air out of the lungs.