During breathing in humans, the contraction of external intercostal muscles causes
Correct answer: B. Outward movement of ribs
- A. Compression of the rib cage
- B. Outward movement of ribs
- C. Inward movement of sternum
- D. Relaxation of the diaphragm muscles
Explanation
The contraction of the external intercostal muscles during inhalation causes the ribs to move outward and upward. This action increases the volume of the thoracic cavity, allowing the lungs to expand and fill with air. Option B is correct because it describes this outward movement of the ribs. Option A is incorrect because compression of the rib cage would reduce lung volume, which is not the intended effect during inhalation. Option C is incorrect because the sternum moves outward, not inward, as the ribs move outward. Option D is incorrect because during inhalation, the diaphragm actually contracts and moves downward, which is the opposite of relaxation.
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About Human Respiratory System
The human respiratory system conducts air to the alveoli, where oxygen and carbon dioxide exchange occurs across thin respiratory surfaces. Questions cover the nasal passage, trachea, bronchi, lungs, diaphragm and intercostal muscles, ventilation mechanics and gas transport, while distinguishing breathing and gaseous exchange from cellular respiration.
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