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

Options

A. Internal intercostal muscles relex and diaphragm contracts
B. External intercostal muscles and diaphragm relax
C. internal intercostal muscles contract and diaphragm ralax
D. External intercostal muscles and diaphragma contract

Answer

C

Explanation

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