Question

Contraction of diaphragm increases the volume of the thoracic chamber in the $ \, ......(A)...... \, $ axis while the contraction of external intercostal muscles increases the volume of the thoracic chamber in the .......(B)...... axis.

• A. $\left(A\right):$ antero-posterior, $\left(B\right):$ antero-posterior
• B. $\left(A\right):$ dorso-ventral, $\left(B\right):$ dorso-ventral
• C. $\left(A\right):$ antero-posterior, $\left(B\right):$ dorso-ventral
• D. $\left(A\right):$ dorso-ventral, $\left(B\right):$ antero-posterior

Answer 1

Answer: (C)

External intercostal muscles and diaphragm play an important role in the inspiration and expiration of gases. During inspiration, there is the movement of oxygen inside the lungs i.e. oxygen moves from high pressure to low pressure as the volume of the lung cavity is in an expanded state, and movement of gases follows Boyle's law. The contraction of external intercoastal muscles and diaphragm causes this increase. External intercostal muscles when contract they pull the ribs and sternum outwards and thus the increase of lung cavity is in dorso-ventral axis. When diaphragm contracts it is pulled downwards and thus the increase of lung cavity is in antero-posterior axis.