When does passive exhalation occur in the normal ventilation cycle?

Passive exhalation is a process that occurs when the diaphragm and intercostal muscles relax, allowing the elastic recoil of the lungs and thoracic cavity to occur. This mechanism is vital for returning air from the lungs to the atmosphere without the need for muscular effort.

The correct choice highlights that passive exhalation specifically follows the relaxation of the diaphragm, which is the primary muscle involved in the process of inhalation. When the diaphragm contracts, it flattens and increases the volume of the thoracic cavity, resulting in air being drawn into the lungs. Once inhalation is complete and the diaphragm returns to its resting position, the decrease in thoracic volume causes air to be expelled from the lungs naturally. This is due to the elastic properties of the lung tissue and the thoracic cavity, which push the air out during exhalation.

Each of the other options relates to different aspects of the ventilation cycle but does not specifically denote the moment when passive exhalation occurs. Active inhalation involves muscular contraction, while stating that passive exhalation happens after muscle contraction wouldn't be accurate, as it's the relaxation of those muscles that facilitates the exhalation. Indicating that passive exhalation takes place when the lungs are fully inflated suggests a misunderstanding of