Final answer:
On inspiration, the pressure inside the thoracic cavity decreases as the volume of the cavity increases due to the contraction of the diaphragm and intercostal muscles, in accordance with Boyle's Law.
Step-by-step explanation:
During inspiration, the pressure in the thoracic cavity is decreased. This is due to Boyle's Law, which states that the pressure of a gas is inversely proportional to its volume. When the diaphragm contracts and the intercostal muscles pull the rib cage upward and outward, the volume of the thoracic cavity increases, causing a drop in pressure relative to the ambient air pressure. Consequently, air is drawn into the lungs to equalize the pressure, as air moves from a region of higher pressure to one of lower pressure. This process relies on pulmonary ventilation mechanics where thoracic wall compliance plays a role, ensuring that the thoracic wall can stretch sufficiently to allow the lungs to expand during inspiration.