During inhalation, which statement best describes the action of the diaphragm?

• A. It contracts and pulls upward.
• B. It relaxes and moves downward.
• C. It expands the chest cavity during exhalation.
• D. It contracts and pulls downward, expanding the thoracic cavity.

Answer: (D)

During inhalation, the diaphragm contracts and moves downward, flattening as it descends. This increases the vertical size of the thoracic cavity, creating negative pressure that pulls air into the lungs. If the diaphragm relaxed or moved upward, there wouldn’t be the necessary change in chest volume to draw air in. Exhalation, by contrast, involves the diaphragm relaxing and rising, which reduces thoracic volume.