The breastbone, also known as the sternum, is a flat bone positioned at the center of the chest. It is a significant component of the human skeletal system, located in the anterior aspect of the thorax along the midline. This singular bone contributes to the overall framework of the upper body.
Structure and Position
The breastbone is a flat, T-shaped bone, approximately 6 inches long in adults. It consists of three distinct segments that fuse together: the manubrium, the body, and the xiphoid process. These parts are joined by cartilage in children, which ossifies into bone during adulthood.
The manubrium is the uppermost and widest part of the breastbone, resembling a handle. It has a quadrangular shape and features a concave depression at its superior aspect called the jugular notch. The manubrium articulates with the clavicles and the cartilages of the first pair of ribs, along with part of the second rib. Directly below the manubrium lies the body of the sternum, the longest section. This central part is flat and narrow, providing attachment points for the costal cartilages of the second through seventh ribs.
The lowest and smallest segment of the breastbone is the xiphoid process, pointed or triangular in shape. It is primarily composed of cartilage in younger individuals and gradually hardens into bone as a person ages. The xiphoid process is located at the level of the T10 vertebra and serves as the anterior limit of the thoracic outlet. Its variable size and shape contribute to individual anatomical differences.
Protective Role and Connections
The breastbone is a central part of the rib cage, working with the ribs to create a protective framework for vital internal organs. Its position at the front of the chest helps shield the heart, lungs, esophagus, and major blood vessels from external injury. This protective function safeguards delicate structures within the thoracic cavity.
Beyond protection, the breastbone serves as a significant attachment point for various bones and muscles. It connects directly to the first seven pairs of ribs via costal cartilages, forming the anterior portion of the rib cage. The eighth, ninth, and tenth ribs are indirectly attached to the breastbone through the costal cartilage of the ribs above them. This intricate connection provides structural integrity to the chest and allows for flexibility during respiration.
Several muscles also anchor to the breastbone, contributing to movements of the chest, neck, and abdomen. For instance, muscles like the pectoralis major attach to the body and manubrium, while the diaphragm attaches to the xiphoid process. The attachment of abdominal muscles, such as the rectus abdominis and obliques, to the xiphoid process further highlights its role in supporting the abdominal wall. This network of connections allows the breastbone to facilitate chest expansion and contraction during breathing.