To breathe in (inhale), you use the muscles of your rib cage, particularly the diaphragm. Your diaphragm contracts and flattens, allowing you to inhale air. When you exhale, the muscles in your diaphragm and rib cage relax. This naturally expels air from your lungs. The diaphragm is a dome-shaped muscle that separates the chest from the abdomen. It functions like a bellows, expanding during inhalation and contracting during exhalation. The diaphragm controls how much air enters your lungs and how it is distributed throughout your lung tissue. Without a healthy diaphragm, you would be unable to breathe because it is this muscle that allows you to expand your ribcage and take in more air. The phrenic nerve supplies movement to the diaphragm. If you injure or sever this nerve, you will die without oxygen. However, if you heal such an injury, the muscle mass of the diaphragm will remain paralyzed due to the lack of stimulation from the phrenic nerve. You must use another source of power for breathing until the diaphragm recovers. During pregnancy, the diaphragm expands to allow for the growth of the fetus. After childbirth, the diaphragm typically returns to its pre-pregnant size but may never fully recover its strength.