Question

Which of the following contracts during normal inspiration?

• A. Diaphragm
• B. Abdominal muscles
• C. Internal intercostal muscles
• D. External intercostal muscles

Answer 1

Answer: (A), (D)

The correct options are
A

Diaphragm

D

External intercostal muscles

During normal inspiration, the diaphragm and the external intercostal muscles contract. The diaphragm moves downwards increasing the volume of the thoracic (chest) cavity, and the intercostal muscles pull the ribs up expanding the rib cage and further increasing its volume. An increase in pulmonary volume decreases the intrapulmonary pressure to less than the atmospheric pressure which forces the air from outside to move into the lungs, which is inspiration.