1. Brain signals the phrenic nerve
2. Phrenic nerve stimulates the diaphragm (muscle) to contract
3. When diaphragm contracts it moves down making the thoracic cavity larger
4. When volume increases, pressure decreases
5. Air moves from are of higher pressure (atm) to an area of lower pressure (lungs)
6. When alveolar pressure becomes equal to atmospheric pressure, thorax stops expanding and airflow stops
