Question

During expiration the diaphragm___________________ and the volume of the thoracic cavity____________________ .

• A. relaxes, increases
• B. contracts, decreases
• C. relaxes, decreases
• D. contracts, increases

Answer 1

The correct option is C relaxes, decreases

Expiration is a process in which air is drawn out of the lungs. During expiration, the diaphragm (a dome-shaped muscle that separates the chest cavity and the abdominal cavity) relaxes and returns back to its usual position. The volume of the thoracic cavity (cavity that is enclosed by the vertebral column, ribs and the sternum) decreases in the longitudinal direction. The external intercostal muscles also relax and the thoracic cavity contracts in the dorsoventral direction.