75% respiration is due to:

Ans. A DiaphragmRef: Snell Anatomy, 7h ed. pg 499; BDC 6th ed. vol. I pg. 212-13* Diaphragm is major respiratory muscle* Inspiration is an active process and requires contraction of inspiratory muscles.* During quiet breathing expiration is a passive process.* During inspiration all the 3 dimensions of the thoracic cavity expand# Vertical-75% (by diaphragm)# AP 25% (external intercostals and internal intercostals)# Transverse# Increase in vertical diameter is brought about by downward movement of diaphragm--which account for 70% of the thoracic expansion.