A) External intercostal muscles relax and diaphragm contracts
B) External intercostal muscles contract and diaphragm relaxes
C) External intercostal muscles and diaphragm relax
D) External intercostal muscles and diaphragm Contract
Correct Answer: C
Solution :
[c] When the external intercostal muscles 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).
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