Question

During inspiration in humans,

• A. contraction of diaphragm increases the volume of thoracic cavity in antero-posterior axis
• B. relaxation of diaphragm increases the thoracic volume in antero-posterior axis
• C. contraction of internal intercostal muscles increases the volume of thoracic cavity in antero-posterior axis
• D. relaxation of internal intercostal muscles decreases the volume of thoracic cavity in dorso-ventral axis

Answer 1

The correct option is A contraction of diaphragm increases the volume of thoracic cavity in antero-posterior axis

During normal inspiration, contraction of diaphragm and external and internal intercostal muscle increases the thoracic volume. Inspiration is initiated by the contraction of diaphragm which increases the volume of thoracic chamber in the antero-posterior axis. The contraction of external intercostal muscles lifts up the ribs and the sternum causing an increase in the volume of the thoracic chamber in the dorso-ventral axis.