Question

The given figure shows a model demonstrating the mechanism of breathing. What is incorrect about the model?

• A. During inhalation diaphragm moves downwards.
• B. During exhalation lungs reduce in size.
• C. During inhalation and exhalation, rib cage does not move.
• D. During inhalation and exhalation, windpipe does not move.

Answer 1

The correct option is C During inhalation and exhalation, rib cage does not move.

Inspiration occurs when the inspiratory muscles that is, the diaphragm and the external intercostal muscles contract. Contraction of the diaphragm causes an increase in the size of the thoracic cavity, while contraction of the external intercostal muscles elevates the ribs and sternum. Thus, both muscles cause the lungs to expand, increasing the volume of their internal air passages. In response, the air pressure inside the lungs decreases below that of air outside the body. Because gases move from regions of high pressure to low pressure, air rushes into the lungs. Expiration occurs when the diaphragm and external intercostal muscles relax. In response, the elastic fibers in lung tissue cause the lungs to recoil to their original volume. The pressure of the air inside the lungs then increases above the air pressure outside the body, and air rushes out.