Inspiration is the process during which the atmospheric air is taken in.

Mechanism

The diaphragm and the set of intercostal muscles aid in the process of inspiration. The diaphragm contracts, thus increasing the volume of the thoracic cavity in the antero-posterior axis. The intercostal muscles also contract and lifts the ribs up further increasing the volume in the dorso-ventral axis. This creates a negative pressure in the lungs with respect to the atmospheric pressure. The air rushes in to equalise the pressure.