Which process occurs when the inspiratory muscles return to their resting position after inhalation?

• A. Elastic rebound
• B. Intrapulmonary expansion
• C. Pleural compression
• D. Cardiac contraction

Answer: (A)

Elastic rebound is the process at work. After the inspiratory muscles relax, the lungs’ elastic fibers and the surface tension inside the alveoli pull the lung tissue back toward its resting size, and the chest wall recoils as well. This return to resting dimensions increases the pressure inside the airways above atmospheric pressure, driving air out and ending inhalation. The other options don’t fit because they describe things that aren’t how normal, passive expiration occurs: expanding the lungs after inhalation would be ongoing inspiration, “pleural compression” isn’t a standard driver of breathing, and cardiac contraction relates to the heart, not the mechanics of returning the inspiratory muscles to rest.