Final answer:
During inhalation, the diaphragm contracts and moves downwards, while the external intercostal muscles contract and expand the rib cage, drawing air into the lungs. During exhalation, the diaphragm relaxes and moves upwards, and the rib muscles relax, forcing the air out of the lungs.
Step-by-step explanation:
During inhalation, the diaphragm contracts and moves downwards, while the external intercostal muscles contract and expand the rib cage, increasing the volume of the thoracic cavity. This leads to a decrease in intra-alveolar pressure, creating a pressure lower than atmospheric pressure and drawing air into the lungs. On the other hand, during exhalation, the diaphragm relaxes and moves upwards, and the rib muscles relax, decreasing the volume of the thoracic cavity. This increase the air pressure inside the lungs, causing air to be forced out of the lungs and into the atmosphere.