Origin: From the inner surfaces of the lower six ribs, from the back of the xiphisternum, from the right and left crura which are attached, respectively, to the upper three and the upper two lumbar vertebrae, and from the medial and lateral arcuate ligaments which bridge over the psoas major and quadratus lumborum.
Insertion: The fibres (striated muscle) are inserted into the central tendon.
Actions: The diaphragm is involved in respiration. When the muscle fibres contract, the diaphragm is lowered, thus increasing the vertical dimension of the thorax. In the later stages of contraction, using the liver as a fulcrum it raises the lower ribs, thus increasing the width of the lower thorax. At the same time, it increases the intra-abdominal pressure and is thus used in expulsive efforts—defecation, micturition, parturition, etc.
Nerve supply: Phrenic nerve (C3, 4 and 5).
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