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Question

Choose the events during a normal expiration.

I. Diaphragm contracts
II. External inter-costal muscles relax
III. External inter-costal muscles contract
IV. Internal inter-costal muscles expand
V. Diaphragm relaxes

A
I, II and IV
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B
II and V
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C
III, IV and V
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D
III and IV
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Solution

The correct option is B II and V
The physical process of breathing includes inspiration (inhalation) and expiration (exhalation). The rib cage, the external and internal inter-costal muscles (rib cage muscles) and the diaphragm are involved in the process of breathing.

During normal expiration, the diaphragm relaxes and becomes dome shaped, the external inter-costal muscles relax pushing the rib cage inwards and downwards. The thoracic volume decreases, causing an increase in the pulmonary pressure and forces the air to move out from the lungs.

During inspiration, the dome shaped diaphragm gets flattened (contracts) and the external inter-costal muscles contract pulling the rib cage upwards and forward. This leads to an increase in the thoracic volume, the pulmonary pressure drops and the air from outside moves into the lungs.

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