- A Contraction in diaphragm
- B Contraction in external intercostal muscle
- C Contraction in internal intercostal muscle
- D Sternum moves upward
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Answer:
C
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During normal inspiration, the diaphragm and external intercostal muscles contract, which increases the volume of the thoracic cavity. This expansion of the thoracic cavity causes the ribs to move outward and the sternum to move upward. However, the internal intercostal muscles are involved in forced expiration, not normal inspiration. These muscles contract during forced expiration to decrease the volume of the thoracic cavity and expel air from the lungs.
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