Answer:
Inspiration (breathing in)
The diaphragm contracts and moves downwards. The intercostal muscles contract and move the ribs upwards and outwards. This increases the size of the chest and decreases the air pressure inside it which sucks air into the lungs. During normal breathing, the major inspiratory muscles produce rib cage expansion and a downward movement of the diaphragm. These movements cause the pressure around and in the lung to become negative (relative to atmospheric pressure).
Explanation:
