Question

Which muscle contracts during a normal expiration?

• A. Diaphragm
• B. Internal intercostal muscles
• C. Abdominal muscles
• D. None of the above

Answer 1

The correct option is D None of the above

The process of respiration is categorised into two distinct phases. The first phase is inspiration or inhaling. When the lungs inhale, the diaphragm (thin muscular layer present beneath the lungs) contracts and it pulls downward. Simultaneously, the external intercostal muscles between the ribs contract and pull upward. It results in an increment of the size of the thoracic cavity and a decrement in the pressure inside. After the process of inspiration, air fills the lungs.

The next phase is termed expiration or exhaling. When the lungs exhale, the diaphragm relaxes, and the volume of the thoracic cavity decreases along with an increase in the pressure. As a result, the air is forced out of the lungs. In forced inspiration, muscles of the neck contract, and the thoracic wall is lifted. This results in an increment of lung volume. In forced expiration, accessory muscles of the abdomen contract, forcing organs in the abdomen upward against the diaphragm.