Explain the mechanism of breathing with neat labelled sketches.

Explanation

Mechanism of respiration invoves the alternate expansion and contraction of thoracic cavity (called respiratory movements ) which cause changes in intrapulmonary pressure in relation to enviroment. Man respires at an avrage rate of 12 times per minute. mechanism invokves two phases:
(A) Inspiration (inhalation ) :
(b) Expiration (Exhalation): it involves expelling of foul air out of body. At rest it is a passive process and simply involves relaxation of phrenic muscles (inspiratory muscles). but during forcefulexpiration, it also involves contraction of expiratory muscles.
( ii) Internal intercostal muscles whose contraction pull the ribs downward and inward. this decreases thoracic cavity dorsoventrally.
Decrease in thoracic cavity increases intrapulmonary pressure than atmospheric pressure. pulmonary pressure than atmospheric pressure. so about 500ml. of foul air is expelled out through respiratory tract.