The thoracic diaphragm, or simply the diaphragm (Ancient Greek: διάφραγμα, romanized: diáphragma, lit. 'partition'), is a sheet of internal skeletal muscle in humans and other mammals that extends ...
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across the bottom of the thoracic cavity. The diaphragm is the most important muscle of respiration, and separates the thoracic cavity, containing the heart and lungs, from the abdominal cavity: as the diaphragm contracts, the volume of the thoracic cavity increases, creating a negative pressure there, which draws air into the lungs. Its high oxygen consumption is noted by the many mitochondria and capillaries present; more than in any other skeletal muscle.