During inhalation in humans, which coordinated muscular movements increase the volume of the thoracic cavity?
Answer and explanation
Correct answer: A. Diaphragm contracts and flattens, intercostal muscles contract lifting the ribs
- Step 1: Inhalation is an active process: the diaphragm contracts and flattens downwards.
- Step 2: Simultaneously, external intercostal muscles contract, lifting the ribs and sternum upwards and outwards.
- Step 3: This expands thoracic volume, lowering intra-alveolar pressure below atmospheric pressure to draw air in.
Answer
Diaphragm contracts and flattens, intercostal muscles contract lifting the ribs.
Why not the others: Diaphragm relaxation and downward rib movement occur during passive exhalation, which decreases thoracic volume.
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