What happens to the ribs and chest when the external intercostal muscles contract during inspiration?

• A. They elevate to increase thoracic volume
• B. They lower to decrease thoracic volume
• C. They remain static
• D. They retract to compress thoracic volume

Answer: (A)

When the external intercostal muscles contract during inspiration, they elevate the ribs. This elevation increases the thoracic volume, creating a negative pressure within the thoracic cavity. As a result, air is drawn into the lungs due to the pressure gradient between the atmosphere and the negative pressure inside the thorax.

This action is fundamental in the mechanics of ventilation, as the increase in thoracic volume not only facilitates the expansion of the lungs but also ensures that more air enters the pleural space, promoting effective gas exchange. Proper understanding of this process is essential for grasping how the respiratory system operates during the act of breathing.