inspiration

• During inspiration, the external intercostal muscles contract whereas the internal ones relax, as a result cause the ribs to raise upwards. The diaphragm contracts and flattens.
• In combination, the intercostal muscles and diaphragm cause the volume inside the thorax to increase, thus lowering the pressure. The difference between the pressure inside the lungs and atmospheric pressure creates a gradient, thus causing the air to enter the lungs