Question

Mark the correct pair of muscles involved in the normal breathing in humans during expiration.

• A. External and internal intercostal muscles
• B. Diaphragm and abdominal muscles
• C. Diaphragm and internal intercostal muscles
• D. Diaphragm and external intercostal muscles

Answer 1

The correct option is

C

Diaphragm and external intercostal muscles

Expiration is initiated by the relaxation of the diaphragm and the intercostal muscles, which returns the diaphragm and sternum to their normal positions and reduces the thoracic volume and thereby the pulmonary volume. This leads to an increase in intra-pulmonary pressure to slightly above the atmospheric pressure causing the expulsion of air from the lungs, i.e., expiration. Thus, it is the diaphragm and intercostal muscles that play a major role in expiration.