Final answer:
During inspiration, the diaphragm and external intercostal muscles contract, causing the thoracic cavity to expand. This creates a lower pressure in the lungs than the atmosphere, resulting in air flowing into the lungs.
Step-by-step explanation:
Inspiration refers to the process of inhalation, where air enters the lungs.
During inspiration, the diaphragm and external intercostal muscles contract, causing the thoracic cavity to expand.
This increase in volume leads to a decrease in intra-alveolar pressure, creating a pressure lower than atmospheric pressure.
As a result, a pressure gradient is created that drives air into the lungs.