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In inhalation, the diaphragm contracts (to straighten) and the intercostal muscles contract (to
move the ribcage upwards and outwards). This increases the volume inside the chest cavity,
and therefore decreases the pressure. The pressure inside the chest cavity is now less than that
of the air outside it, so the air diffuses in following the pressure gradient.
In exhalation, the diaphragm relaxes and the intercostal muscles relaxes, which makes the
ribcage move down and inwards.…read more


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