The diaphragm is the muscle that separates the human chest cavity from the abdominal cavity and powers most breathing.
This dome-shaped sheet of skeletal muscle sits beneath the lungs. When it contracts, it moves downward and increases the volume of the thoracic cavity. The resulting pressure decrease draws air into the lungs. When it relaxes, it rises and helps air leave.
Although the diaphragm performs most of the work of quiet inhalation, the external intercostal muscles also assist by moving the ribs. During forceful breathing, additional muscles in the neck, chest, and abdomen can contribute.
The diaphragm has openings for major structures, including the esophagus, aorta, and inferior vena cava. Its name comes from the Greek word diaphragma, meaning a partition. A hiccup is an involuntary contraction of the diaphragm followed by closure of the vocal folds.