Inhalation requires the contraction of what structure?

The diaphragm is a large, dome-shaped muscle that separates the chest cavity from the abdominal cavity. It is located below the lungs and above the stomach and intestines.
When the diaphragm contracts, it flattens and moves downward. This increases the volume of the chest cavity, which causes the lungs to expand. As the lungs expand, air rushes in through the nose and mouth.