Question

How many of the following given statements are not correct w.r.t. the events that occur during inspiration?
(a) Relaxation of diaphragm
(b) Contraction of external inter-costal muscles
(c) Volume of thoracic cavity decreases
(d) Intra-pulmonary pressure increases

Choose the suitable option among the following given options.

• A. One
• B. Two
• C. Three
• D. Four

Answer 1

The correct option is C Three

Inspiration is initiated by the contraction of diaphragm which increases the volume of thoracic chamber in the antero-posterior axis. The contraction of external inter-costal muscles lifts up the ribs and the sternum causing an increase in the volume of the thoracic chamber in the dorso-ventral axis.

The overall increase in the thoracic volume causes a similar increase in pulmonary volume. An increase in thoracic volume decreases the intra-pulmonary pressure to less than the atmospheric pressure which forces the air from outside to move into the lungs, i.e., inspiration.