Inspiration (breathing in) - active process
Intercostal muscles and diaphragm contract (flatten)
Rib cage moves upwards and outwards
This increases the volume of the thorax so pressure decreases below atmospheric pressure
This causes air to flow into lungs
Expiration (breathing out) - passive process
Intercostal muscles and diaphragm relax (domes)
Rib cage moves downwards and inwards
This decreases the volume of thorax so pressure increases above atmospheric pressure
Air is forced out of the lungs
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