The floor of the room is your diaphragm. This large muscle moves up and down making the room smaller and larger. When you breathe in, the diaphragm contracts and drops down. At the same time, your ribs expand outward. The chest cavity room gets larger.
Air rushes in to fill the space.
When you breathe out, the diaphragm relaxes into it up position. The ribs settle down. The space in the room shrinks and the air is squeezed out of the lungs. More Challenges Share your lung model with someone else and explain how the lungs work. Contact the American Lung Association to find out about how to keep your lungs healthy.