Final answer:
During inspiration, the contraction of the external intercostal muscles expands the rib cage while the diaphragm contracts and moves downward, increasing thoracic volume and allowing air to enter the lungs.
Step-by-step explanation:
During inspiration, the diaphragm and external intercostal muscles contract, playing a major role in the process of breathing. The contraction of the external intercostal muscles causes the rib cage to expand and move outward, which increases the volume of the thoracic cavity. At the same time, the diaphragm moves downward toward the abdominal cavity, further increasing the space available for the lungs to expand. This coordinated movement causes the pressure inside the lungs to decrease below atmospheric pressure, resulting in air being drawn into the lungs for respiration.
During inspiration, the external intercostal muscles contract and the diaphragm moves downward. This movement of the diaphragm creates more space in the thoracic cavity, causing the lungs to expand and air to be drawn into the lungs. Additionally, the contraction of the external intercostals moves the rib cage upward and outward, further increasing the volume of the thoracic cavity.