Final answer:
The process of breathing, known as pulmonary ventilation, involves inspiration and expiration, primarily driven by the diaphragm and external intercostal muscles. These muscles modify thoracic cavity volume, enabling air to flow in and out of the lungs, while muscles like Levatores Costarum play roles in more active respiratory efforts.
Step-by-step explanation:
Pulmonary ventilation, consisting of inspiration and expiration, involves several muscle groups, with the diaphragm and external intercostal muscles playing key roles during normal respiration.
During the process of inspiration, which causes air to enter the lungs, the diaphragm contracts and moves down towards the abdominal cavity, enlarging the thoracic cavity and allowing for lung expansion. Concurrently, the external intercostal muscles contract to move the ribs upward and outward, further increasing the volume of the thoracic cavity and decreasing intra-alveolar pressure. This results in a pressure gradient that causes air to flow into the lungs due to the atmospheric pressure being greater.
For expiration, which is the process of air leaving the lungs, the diaphragm and intercostal muscles relax, causing the thoracic cavity to decrease in volume and forcing air out of the lungs. However, during forced expiration, the internal intercostal muscles and abdominal muscles may be actively involved. Understanding the role of muscles like the Levatores Costarum in breathing can help pinpoint the processes and structures involved in both voluntary and involuntary respiration.