Breathing
The lungs are located in the thoracic cavity, which is surrounded by the ribs and the diaphragm. Because the lungs do not have muscles of their own, they cannot move by themselves.
Instead, movements of the ribs and diaphragm cause the volume of the lungs to increase or decrease.
For example,
- Ribs move upward and the diaphragm moves downward → the thoracic cavity expands → lung volume increases → pressure inside the lungs decreases → outside air enters the lungs (inhalation)
- Ribs move downward and the diaphragm moves upward → the thoracic cavity becomes smaller → lung volume decreases → pressure inside the lungs increases → air leaves the lungs (exhalation)
This is how breathing takes place.