THORAX ABDOMEN AND PELVIS

Detailed explanation-1: -The diaphragm, located below the lungs, is the major muscle of respiration . It is a large, dome-shaped muscle that contracts rhythmically and continually, and most of the time, involuntarily. Upon inhalation, the diaphragm contracts and flattens and the chest cavity enlarges.

Detailed explanation-2: -Upon exhalation, the lungs recoil to force the air out of the lungs, and the intercostal muscles relax, returning the chest wall back to its original position (Figure 2b). The diaphragm also relaxes and moves higher into the thoracic cavity.