Emergency Medical Responder Practice Exam

During a normal respiration cycle, the primary actions involve the mechanics of inhalation and exhalation, which are driven by changes in chest volume and pressure. When a person inhales, the diaphragm, a dome-shaped muscle beneath the lungs, contracts and moves downward. This contraction increases the volume of the thoracic cavity (the chest), leading to a decrease in pressure within the lungs compared to the outside atmospheric pressure. As a result, air flows into the lungs due to this pressure gradient, allowing for effective gas exchange.

The increase in chest volume combined with the decrease in pressure is crucial for allowing air to enter the lungs easily during inhalation. This fundamental principle is dictated by Boyle's law, which states that at constant temperature, the pressure and volume of a gas are inversely related. Therefore, option B accurately describes the key physiological changes that occur in the lungs during inhalation in a normal respiration cycle.