External intercostals muscles Actively contract
- Ribs and sternum move upwards and outwards
- Width of chest increases from side to side, from front to back and from top to bottom
Diaphragm contracts
- Descends
- Depth of chest increases
Capacity of thorax is increased
Pressure between pleural surfaces is reduced.
Elastic tissue of lungs is stretched.
Lungs Expand to fill thoracic cavity
Air pressure within alveoli is now less than atmospheric pressure
Air is sucked into alveoli from atmosphere