Question

Select the correct events that occur during inspiration.
(a) Contraction of diaphragm
(b) Contraction of external intercostal muscles
(c) Pulmonary volume decreases
(d) Intra-pulmonary pressure increases

• A. (a), (b) and (d)
• B. Only (d)
• C. (a) and (b)
• D. (c) and (d)

Answer 1

The correct option is C (a) and (b)

Breathing involves inspiration and expiration.

Inspiration is a process in which the air is drawn into the lungs and during expiration, the air is released out.

During inspiration, the diaphragm (dome-shaped muscle that separates the chest cavity and the abdominal cavity) contracts because of which it gets pulled down and this increases the volume of the thoracic chamber in the antero-posterior axis.

The external intercostal muscles present between the successive ribs also contract. Due to this the ribs and sternum are lifted upwards causing an increase in the volume of the thoracic chamber in the dorso-ventral axis.

Due to the expansion of the thoracic cavity, the volume inside the lungs (pulmonary volume) increases. An increase in pulmonary volume decreases the intra-pulmonary pressure.

Thus, during inspiration, the pressure within the lungs (intra-pulmonary pressure) is less than that of atmospheric pressure.

As a result of this, the air moves into the lungs from the atmosphere.