Musculoskeletal System: Thorax

The chest wall consists of skin, fat, muscles, bones, and cartilage. The bony structure of the chest wall is composed of the ribs, sternum, and thoracic vertebrae. The chest wall serves as armor for the vital intrathoracic organs and provides the stability necessary for the movement of the shoulders and arms. The interconnections between the bones, cartilage, and muscles allow for the rhythmic expansion and reduction of the chest wall during breathing, which facilitates changes in intrathoracic pressure to allow expansion of the lungs during inspiration. The extrinsic muscles have 2 bony attachments; the intrinsic muscles only attach to the thoracic skeleton.

The diaphragm is a large, dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. The diaphragm consists of muscle fibers and a large central tendon, which is divided into right and left parts. As the primary muscle of inspiration, the diaphragm contributes 75% of the total inspiratory muscle force, and its contraction leads to flattening of the dome of the diaphragm. This flattening increases the volume of the thoracic cavity and allows the lungs to expand during inspiration.

The pleura is a serous membrane that lines the walls of the thoracic cavity and the surface of the lungs. This structure of mesodermal origin covers both lungs, the mediastinum, the thoracic surface of the diaphragm, and the inner part of the thoracic cage. The pleura is divided into a visceral pleura and parietal pleura. Between both layers, there is a well-lubricated potential space called the pleural cavity, which eases the respiratory movements of the lungs and helps avoid friction.