Diaphragm

Diaphragma

MuscularDeep musclesAbdomen

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What it is

Dome-shaped musculotendinous sheet separating the chest from the abdomen. Its muscle fibres arise from the xiphoid process, the inner surfaces of the lower six ribs and costal cartilages, the arcuate ligaments and — through the right and left crura — the upper lumbar vertebral bodies, and converge on the central tendon. The right dome sits higher, over the liver.

Function

The main muscle of breathing: contracting, it flattens and descends, enlarging the chest to draw air in; it also raises abdominal pressure for coughing, vomiting, childbirth and defecation.

Size

About 30 cm across and 2–5 mm thick; the domes reach about the 5th rib, and it descends 1–2 cm in quiet breathing and up to 10 cm in a deep breath.

Clinical note

Supplied by the phrenic nerves ("C3, 4, 5 keeps the diaphragm alive"); irritation of it is felt as shoulder-tip pain.