The Respiratory Organs
The Nose The Pharynx
The Larynx The Trachea, Bronchi, and Bronchioles
The Lungs Ventilation Pulmonary The Respiratory Apparatus
The principle is the same as the one we see in action when we a bicycle tire pump. In that case, pulling on the handle expands an internal air chamber and air flows in. pushing. Pushing on the handle shrinks the air chamber and air flows out.
We exploit this principle with our ribs, or the muscles between them, and our diaphragm. During normal, quiet breathing, we use mostly our rib muscles. As the intercostal muscles draw the ribs closer together, they swing forward and upward because of the way they era hinged on the vertebrae and because if their flexible attachments to the sternum . This movement expands the ribcage and the lungs. During forced inspiration, additional, accessory muscles enhance the expansion. During force expiration, the internal intercostal and abdominal muscles pull the ribs down and shrink the cavity, forcing air out of the lungs.
The diaphragm is a sheet of muscle separating the base of the thoracic cavity from the top of the abdominal cavity. Anchored on the lowermost ribs, it domes up beneath the lungs and heart. When it contracts, it flattens, pushing the abdominal organs downward and expanding the chest cavity and pushing air out of the lungs.
You can watch the two ventilating mechanism
in action if you lie flat on your back on the floor with one on your chest
and the other on your abdomen. When you breathe with your diaphragm, the
first does not move, but the second rises and falls. When you breathe with
your ribs, the second book is motionless, but the first one rises and falls.