The diaphragm is the primary muscle responsible for respiration. Connected to the |abdominal wall|, the lumbar vertebra, the lower |ribs|, the |sternum|, and the |pericardium| of the |heart| by tendinous tissue, the thin diaphragm creates a partition between the thoracic and abdominal cavity. The diaphragm forms a domed structure, and when the diaphragm muscle contracts, it lowers to a more flattened arrangement. This flattening causes a vacuum in the thoracic cavity and pressure in the abdominal cavity. The vacuum is filled by the expanding |lung| tissue and inhaled ~air~. The pressure on the lower viscera are helpful in |childbirth| and in pushing fecal matter through the lower intestinal tract for expulsion. When the diaphragm relaxes to its domed structure, the ~air~ is pushed out (exhaled) and the |lungs| contract. Though the intercostal and abdominal muscles are also used in respiration, during sleep, it is primarily due to |contractions| of the diaphragm.
