Question

By the contraction in which of the following muscle, the volume of thoracic chamber increases in the antero-posterior axis?

• A. Diaphragm muscles
• B. Abdominal muscles
• C. Diaphragm muscles and EICM
• D. External inter-coastal muscles

Answer 1

The correct option is A Diaphragm muscles

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 pulmonary 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.