Question

Which of the following changes occur in diaphragm and intercostal muscles when expiration of air takes place?

• A. Internal intercostal muscles relax and diaphragm contracts
• B. External intercostal muscles and diaphragm relaxes
• C. Internal intercostal muscles contract and diaphragm relax
• D. External intercostal muscles and diaphragm contract

Answer 1

The correct option is C Internal intercostal muscles contract and diaphragm relax

• When the internal intercostal muscles contract and diaphragm relax, the ribs move downward and inward and the diaphragm becomes convex {dome shaped),
• This decreasing the volume of the thoracic cavity and increases the pressure inside as compared to the atmospheric pressure outside. This will cause the air to move out (expiration).