<Tr> <Td_colspan="2"> Anatomical terminology (edit on Wikidata) </Td> </Tr> <P> The muscles of respiration are those muscles that contribute to inhalation and exhalation, by aiding in the expansion and contraction of the thoracic cavity . The diaphragm and, to a lesser extent, the intercostal muscles drive respiration during quiet breathing . Additional' accessory muscles of respiration' are typically only used under conditions of high metabolic demand (e.g. exercise) or respiratory dysfunction (e.g. an asthma attack). </P> <P> The diaphragm is the major muscle responsible for breathing . It is a thin, dome - shaped muscle that separates the abdominal cavity from the thoracic cavity . During inhalation, the diaphragm contracts, so that its center moves caudally (downward) and its edges move rostrally (upward). This compresses the abdominal cavity, raises the ribs upward and outward and thus expands the thoracic cavity . This expansion draws air into the lungs . When the diaphragm relaxes, elastic recoil of the thoracic wall causes the thoracic cavity to contract, forcing air out of the lungs . </P> <P> The diaphragm is also involved in non-respiratory functions, helping to expel vomit, faeces, and urine from the body by increasing intra-abdominal pressure, and preventing acid reflux by exerting pressure on the esophagus as it passes through the esophageal hiatus . </P>

When are the abdominal muscles involved in breathing
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