Internal intercostal muscle contraction in respiration

Steps:

• Identify the intercostal muscles: diagram shows internal intercostals between ribs.
• Recall function: internal intercostals contract to pull ribs downward and inward.
• Link to thoracic cavity: downward rib movement decreases thoracic volume.
• Conclude effect: this aids expiration by reducing lung space.

Why D is correct:

• Internal intercostal contraction directly pulls adjacent ribs downward, as defined in respiratory anatomy for forced expiration.

Why the others are wrong:

• A: Diaphragm movement is controlled by its own contraction, not intercostals.
• B: Lung inflation occurs during inspiration via external intercostals and diaphragm.
• C: Intrapulmonary pressure decreases during inspiration, not from internal intercostal action.

Final answer: D