Abstract
The diaphragm is the muscle separating the thoracic and abdominal cavities; it is unique to mammals. It arises from the crura, the arcuate ligaments, the costal margin and the posterior aspects of the xiphoid and has a central trefoil-shaped tendon. It has three major openings for the aorta, inferior vena cava and oesophagus. Its entire motor supply and principal sensory supply is from the phrenic nerve (cervical segments 3, 4 and 5). Division of the phrenic nerve results in complete paralysis of the hemidiaphragm, which is elevated by the intra-abdominal pressure. At rest, the diaphragm is at the level of the fifth rib in the mid-clavicular line. In quiet inspiration it descends by about 1.5 cm, but this can increase almost ten-fold in maximal inspiration. Movement of the diaphragm accounts for about 60-75% of the total tidal volume. In quiet respiration it accounts for most, if not all, respiratory movement. The diaphragm also helps to raise the intra-abdominal pressure in defecation, micturition, vomiting and parturition.
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