Inspiration - Air moves from higher to lower pressure , When pressure inside the lungs decreases below atmospheric pressure, air flows in from the atmosphere, Diaphram and intercostal muscles expand during normal inspiration. Diaphram contracts and moves downwards, Due to surface tension between the 2 layers of the pleura, as
the thoracic cavity expands, the lungs expand with it
Expiration - Results from the passive process of elastic recoil of the muscle and lung tissues , The diaphragm and intercostal muscles relax during this time , The diaphragm then gets pushed upward ,As the lungs recoil, the pleura and chest wall are pulled inward
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