ANATOMY

Detailed explanation-1: -The rib cage muscles, including the intercostals, the parasternals, the scalene and the neck muscles, mostly act on the upper part of the rib cage (pulmonary rib cage) and are both inspiratory and expiratory.

Detailed explanation-2: -In addition, the external intercostal muscles participate in inspiration by pulling the ribs abaxially to increase the width of the thoracic cavity. The net effect is an increase in the size of the thoracic cavity, producing subatmospheric intrathoracic pressure, to drive inspiration and pulmonary inflation.

Detailed explanation-3: -The movement of the rib cage is controlled by the intercostal muscles, and the diaphragm is a skeletal muscle. During inspiration the diaphragm and the external intercostal muscles contract, causing an increase in the thoracic cavity volume.

Detailed explanation-4: -The diaphragm, a dome-shaped sheet of muscle that separates the chest cavity from the abdomen, is the most important muscle used for breathing in (called inhalation or inspiration). The diaphragm is attached to the base of the sternum, the lower parts of the rib cage, and the spine.

Detailed explanation-5: -As a result, the external intercostals and the parasternal intercostals have an inspiratory function during breathing, whereas the internal interosseous intercostals and the triangularis sterni have an expiratory function.