What occurs during the lifting of the rib cage by external intercostals?

During the lifting of the rib cage by the external intercostal muscles, inspiration occurs. This is a crucial component of the respiratory process. When these muscles contract, they elevate the ribs and expand the rib cage, which decreases intra-thoracic pressure relative to the atmospheric pressure. As a result, air is drawn into the lungs. This process is integral to breathing, allowing for the intake of oxygen necessary for metabolic processes in the body.

In contrast, expiration (typically associated with the relaxation of these muscles and a subsequent decrease in the volume of the thoracic cavity) does not involve the lifting of the rib cage. Vigilance and cardiac output increase are not directly related to the mechanics of respiration and do not play a role in the physical act of inhalation facilitated by the external intercostals.