Which of the following does NOT occur during inspiration?

• A. The thoracic cavity volume increases
• B. Air flows into the lungs
• C. The diaphragm relaxes
• D. Intrapulmonary pressure decreases

Answer: (C)

Verified step by step guidance

1. Step 1: Begin by understanding the process of inspiration (inhalation). During inspiration, the diaphragm contracts and moves downward, increasing the volume of the thoracic cavity. This is a key mechanism for drawing air into the lungs.
2. Step 2: Recognize that the increase in thoracic cavity volume leads to a decrease in intrapulmonary pressure (pressure within the lungs). This pressure drop creates a pressure gradient that allows air to flow into the lungs.
3. Step 3: Note that air flows into the lungs during inspiration due to the pressure gradient created by the decrease in intrapulmonary pressure. This is a fundamental principle of pulmonary ventilation.
4. Step 4: Understand that the diaphragm does NOT relax during inspiration. Instead, it contracts actively to facilitate the increase in thoracic cavity volume. Relaxation of the diaphragm occurs during expiration (exhalation).
5. Step 5: Based on the above steps, identify that the statement 'The diaphragm relaxes' does NOT occur during inspiration, as it contradicts the physiological process of inhalation.