The sternum, commonly known as the breastbone, is a flat bone situated centrally in the front of the chest. It serves as a prominent component of the thoracic cage, providing protection to vital organs within the chest cavity. The sternum connects with other bones and muscles through cartilage, forming part of the framework that encloses the chest. This bone’s central location makes it readily palpable beneath the skin.
Anatomy and Position
The sternum is composed of three parts: the manubrium, the body (corpus sterni), and the xiphoid process. The manubrium, the uppermost and widest section, has a trapezoid shape and articulates superiorly with the clavicles. It also connects with the first pair of ribs and a portion of the second pair.
At the top of the manubrium, a depression, the jugular notch, is palpable between the clavicles. Inferiorly, the manubrium joins the body of the sternum at a junction known as the sternal angle. This union creates a palpable transverse ridge on the sternum’s anterior surface, which serves as a significant anatomical landmark for locating the second rib.
The body of the sternum forms the longest and largest middle section. It articulates with the costal cartilages of the second through seventh ribs along its lateral borders. The xiphoid process is the smallest, most inferior part of the sternum. Primarily cartilaginous in younger individuals, it gradually ossifies, or turns into bone, as a person ages.
Functions
The sternum plays multiple roles within the human body, providing protection, structural support, and attachment points for muscles. Its flat, bony structure and central placement contribute to safeguarding the heart, lungs, and major blood vessels from external trauma. This protective function is important for the organs housed within the thoracic cavity.
Beyond protection, the sternum contributes to the structural integrity of the rib cage. It acts as an anterior anchor for the ribs, forming a protective cage that helps maintain the shape and stability of the chest cavity. This framework also facilitates breathing, as the sternum and ribs move to allow the chest to expand and contract.
The sternum serves as an attachment site for various muscles in the chest and neck. Muscles such as the pectoralis major and sternocleidomastoid, along with certain abdominal muscles and the diaphragm, connect to the sternum. These muscle attachments are important for movements of the upper limbs, neck stabilization, and breathing.
The sternum is involved in hematopoiesis, the process of blood cell formation. In adults, red bone marrow, which is responsible for producing various blood cells, is found within certain bones, including the sternum. This production of blood cells is a continuous process throughout a person’s life, with the sternum contributing to this function alongside other bones like the vertebrae, hips, and ribs.