During inspiration in a mammal, what happens to the diaphragm and external intercostal muscles?
Answer and explanation
Correct answer: B. The diaphragm contracts and flattens; the external intercostals contract
- Step 1: Contraction of both increases thoracic volume. Step 2. Pressure in the lungs falls below atmospheric, so air flows in. Answer: The diaphragm contracts and flattens; the external intercostals contract. Why not the others: a relaxed diaphragm domes upwards; relaxed external intercostals would not lift the ribs; internal intercostals are used in forced expiration.
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