The rib cage, also known as the thoracic cage, forms a protective bony structure around the upper body. It safeguards internal organs, including the heart and lungs. This framework plays a crucial role in the mechanics of breathing, allowing the chest cavity to expand and contract. The rib cage is composed of 12 pairs of ribs, connecting to the thoracic spine at the back and the sternum (breastbone) at the front.
Muscles That Move Your Ribs
The spaces between your ribs, called intercostal spaces, are occupied by layers of intercostal muscles. These muscles are important for respiration, enabling the expansion and contraction of the chest cavity. There are three main layers: the external, internal, and innermost intercostals.
The external intercostal muscles form the outermost layer, with fibers running downward and forward. They are active during quiet inhalation, contracting to pull the ribs upward and outward, which increases chest cavity volume and draws air into the lungs. These muscles are continuous with the external oblique muscles of the abdomen.
Beneath the external layer are the internal intercostal muscles, whose fibers run downward and backward, perpendicular to the external layer. These muscles are involved in forced exhalation. When they contract, they pull the ribs downward and inward, decreasing thoracic cavity volume and expelling air from the lungs.
The innermost intercostal muscles constitute the deepest layer. Their fiber direction is similar to that of the internal intercostals. Like the internal intercostals, they contribute to forced exhalation by depressing the ribs. All three groups of intercostal muscles provide mechanical support to the rib cage, maintaining its integrity.
Nerves and Vessels of the Rib Cage
The intercostal spaces also house neurovascular bundles that supply the chest wall. These bundles typically run along the underside of each rib, within a protective groove called the costal groove. This arrangement places the vein, artery, and nerve in a consistent order.
Intercostal nerves originate from the thoracic spinal nerves, providing both sensory and motor functions. They transmit sensations from the skin of the chest wall and the parietal pleura, and control the contraction and relaxation of the intercostal muscles. These nerves coordinate movements for breathing.
Intercostal arteries deliver oxygenated blood to the muscles and tissues of the chest wall. Posterior intercostal arteries branch from the aorta, while anterior intercostal arteries arise from the internal thoracic artery. These arteries run alongside the ribs, supplying the surrounding structures.
The intercostal veins collect deoxygenated blood from the chest wall. Posterior intercostal veins drain into the azygos system, while anterior intercostal veins empty into the internal thoracic veins. These vessels work together to maintain the health and function of the intercostal muscles and the entire thoracic wall.
Protective Linings and Spaces
Within the chest cavity, immediately adjacent to the ribs, are the pleura. These are thin, double-layered membranes that protect the lungs. The outer layer, known as the parietal pleura, adheres to the inner surface of the rib cage and the diaphragm.
The inner layer, called the visceral pleura, directly covers the surface of the lungs. Between these two pleural layers lies a potential space, the pleural cavity. This space contains a small amount of serous fluid.
The pleural fluid acts as a lubricant, allowing the parietal and visceral pleura to glide smoothly over each other during breathing. This lubrication minimizes friction as the lungs expand and contract within the rib cage. The fluid also creates a surface tension that helps keep the lungs closely apposed to the chest wall, aiding efficient lung expansion.