Final answer:
Pulmonary ventilation, or breathing, involves the movement of air into and out of the lungs. It consists of inspiration, where air is drawn into the lungs, and expiration, where air is forced out of the lungs. This process is driven by the contraction and relaxation of muscles that expand and recoil the thoracic cavity.
Step-by-step explanation:
Pulmonary ventilation, also known as breathing, is the process of air moving in and out of the lungs. It consists of two steps: inspiration and expiration. During inspiration, the diaphragm and external intercostal muscles contract, expanding the thoracic cavity and causing air to be drawn into the lungs.
During expiration, the diaphragm and intercostals relax, causing the thorax and lungs to recoil and forcing air out of the lungs. The pressure differences created during these steps are responsible for the movement of air in and out of the lungs.