The diaphragm is a dome-shaped muscle located at the base of the lungs that performs the main motion of breathing. The diaphragm contracts downward to pull air into the lungs. The diaphragm can also be used to increase the pressure in the abdomen. There is only one diaphragm in the body, where many muscles have a left and right version.
The diaphragm originates from many points around the lower chest cavity. It attaches to first and second lumbar vertebrae on the left side of the vertebral column, and the first, second, and third on the right side. It also attaches to the six lowest ribs and the sternum.
Because of its dome shape, when the diaphragm contracts, it pulls its middle section downward as the length of the muscle shortens. This downward motion expands the chest cavity and lungs, drawing air into them.