Discussion of the mechanism of breathing. Defining of ventilation, inhalation, and exhalation. Examine how the process involves specific muscles, the intercostal and the diaphragm muscle as well as nerves originating from the respiratory center in the medulla. Discuss briefly the physics of air pressure and the inverse relationship between pressure and the volume of he thorax. As chest volume increases, pressure deceases below atm. pressure, and air rushes into the lungs. In the lab, manufacture lung/chest cavity model using a plastic bottle, balloon, and stretch tight wrap for a diaphragm. Demonstrate the physical process of breathing.