Final answer:
During inhalation, contraction of the diaphragm and external intercostal muscles expands the thoracic cavity, decreasing pressure and allowing air to enter the lungs according to Boyle's Law.
Step-by-step explanation:
When the diaphragm and external intercostal muscles contract, there is a significant change in the volume of the thoracic cavity. The diaphragm flattens and moves downward, while the intercostal muscles raise the rib cage, resulting in an enlargement of the cavity that houses the lungs. This increase in thoracic volume leads to a decrease in intra-thoracic pressure, driving air into the lungs according to Boyle's Law. This process is an essential mechanism of inhalation, an active phase of pulmonary ventilation, which is critical for oxygen intake and carbon dioxide expulsion in respiratory function.
The diaphragm, being a domed muscle separating the thoracic cavity from the abdominal cavity, when contracts, increases the internal volume and decreases the internal pressure, thereby allowing air to rush into the lungs. The external intercostals are accessory muscles of respiration that further augment the thoracic space, facilitating a greater volume of air to enter. These muscle actions maintain the slightly negative pressure vital for keeping the lungs inflated and operational.