The sternum, commonly known as the breast bone, is a flat, T-shaped bone situated at the center and front of the chest. It forms a significant part of the rib cage, providing a central anchor point in the upper torso. You can easily feel it in the middle of your chest. The sternum serves a foundational role in the chest cavity.
Anatomical Components
The sternum is a vertical bone composed of three segments: the manubrium, the body, and the xiphoid process. It is often compared to an upside-down sword, with the manubrium as the handle, the body as the blade, and the xiphoid process as the tip.
The manubrium is the widest, most superior portion of the sternum. It has a concave depression at its upper border, known as the jugular notch. This section articulates with the clavicles, or collarbones, and the first pair of ribs.
Below the manubrium lies the body of the sternum, the longest and flattest part. The manubrium and body join at a slight angle known as the sternal angle, where the second pair of ribs attach. The body provides attachment points for the third through seventh pairs of ribs.
The smallest and most inferior segment is the xiphoid process, a pointed, often triangular projection. This part is primarily made of cartilage in younger individuals and gradually hardens into bone with age. Its shape and size can vary significantly among individuals.
Role in the Body
The sternum performs several functions, primarily acting as a protective shield for organs in the chest. It safeguards structures such as the heart, lungs, and major blood vessels from external trauma. This protective capacity is important for the body’s integrity.
Beyond protection, the sternum serves as a central attachment point for the ribs, forming the front of the rib cage. The first seven pairs of ribs, known as true ribs, connect directly to the sternum via flexible costal cartilages. This connection creates a strong yet flexible enclosure that supports the chest cavity.
The sternum also plays a role in the mechanics of breathing. While the sternum itself does not move independently to facilitate respiration, the cartilaginous connections between the ribs and the sternum allow for slight motions. These small movements enable the rib cage to expand and contract, supporting lung function and effective muscle movement.