NEETZoologyBreathing and Exchange of Gases
What is the role of external intercostal muscles in inspiration?
Options
- AThey contract and lift up the ribs and sternum
- BThey relax and push down the ribs and sternum
- CThey contract and push down the ribs and sternum
- DThey relax and lift up the ribs and sternum
Correct answer
A. They contract and lift up the ribs and sternum
Step-by-step solution
Breathing involves two stages : inspiration during which atmospheric air is drawn in and expiration by which the alveolar air is released out . The movement of air into and out of the lungs is carried out by creating a pressure gradient between the lungs and the atmosphere. Inspiration can occur if the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric pressure, i.e., there is a negative pressure in the lungs with respect to atmospheric pressure. Similarly, expiration takes place when