ventillation

Question 1

what happens during inspiration

Answer 1

external intercostal muscles contract where as the internal ones relax- as a result ribs raise upwards.
The diaphragm contracts and flattens.
In combination, they cause volume inside the thorax to increase, thus lowering pressure.
The difference between pressure inside the lungs and the atmospheric pressure creates a gradient, thus causing air to enter the lungs

Question 2

what happens during expiration ?

Answer 2

internal intercostal muscles contract, external relax, causing rib cage to lower.
the diaphragm relaxes and rises upwards.
This combination decrease the volume inside thorax, increase pressure and force air out of lungs.