describe what happens to the rib cage when the intercostal muscles contract.

When the intercostal muscles contract, specifically the external intercostal muscles during inhalation, they pull the ribs upward and outward. This action causes the rib cage to expand, increasing the volume of the thoracic cavity. As a result, the pressure inside the chest cavity decreases, allowing air to be drawn into the lungs. Conversely, the internal intercostal muscles contract during forced exhalation, pulling the ribs downward and inward, which decreases the thoracic volume and helps push air out of the lungs. In summary, contracting the external intercostal muscles elevates and expands the rib cage, aiding in breathing in, while contracting the internal intercostal muscles lowers the rib cage for breathing out.