The diaphragm is located directly below the lungs. Along with the intercostal muscles (the muscles between the ribs), the diaphragm is a major respiration muscle. The diaphragm is a large, dome-shaped muscle that contracts and flattens during inhalation, which causes the chest cavity to expand. This maneuver creates a vacuum which pulls air into the lungs. During exhalation, the diaphragm then relaxes, returns to its previous shape, and air is forced out of the lungs.