Inspiration in human beings: Inspiration is the process in which we take the air inside the lungs. During this process the lifting of ribs and flattening of the diaphragm takes place. Due to this size of the thoracic cavity increases and pressure inside the lungs remain low as compared to atmospheric pressure and we inhale the air. This process is called inspiration.

Expiration in human beings: Expiration is the process in which we exhale the air outside our lungs. During this process relaxation of the lungs and diaphragm takes place. Due to this the size of thoracic cavity decreases and pressure inside the lungs is high as compared to atmospheric pressure and as a result we exhale the air outside the lungs. This process is called expiration.