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. The abdominal muscles act on the abdomen and the abdominal rib cage and are expiratory.

Detailed explanation-2: -The diaphragm is attached to the base of the sternum, the lower parts of the rib cage, and the spine. As the diaphragm contracts, it increases the length and diameter of the chest cavity and thus expands the lungs. The intercostal muscles and neck muscles help move the rib cage and thus assist in breathing.

Detailed explanation-3: -(c) Diaphragm and external intercostal muscles.

Detailed explanation-4: -The rectus abdominis and internal intercostal muscles are recruited. The first pair increases intra-abdominal pressure, pushing the diaphragm even more upwards. The second pair pull the ribs downwards and inward, further reducing the size of the thoracic cavity.