The rib cage, also known as the thoracic cage, is a fundamental skeletal structure within the human body. It forms the chest cavity, providing a framework that supports the upper torso. This intricate arrangement of bones and cartilage plays a role in various bodily functions.
Bones and Cartilage
The rib cage consists of 24 ribs (12 on each side), along with the sternum (breastbone) and 12 thoracic vertebrae. Each rib is a curved, flattened bone that extends from the back towards the front. The ribs connect posteriorly to the thoracic vertebrae, which are part of the spinal column.
Ribs are categorized into three types based on their anterior attachments. The first seven pairs are “true ribs” because they connect directly to the sternum via their own costal cartilages. The next three pairs (ribs 8-10) are “false ribs”; their costal cartilages do not attach directly to the sternum but instead connect to the cartilage of the rib above them. The last two pairs (ribs 11 and 12) are “floating ribs” as they do not connect to the sternum or other ribs anteriorly, ending within the abdominal muscles.
The Overall Form
The human rib cage presents as a basket-like or conical structure. It is narrower at the top, near the neck, and gradually widens towards the bottom, creating a broad base. This shape is formed by the 12 pairs of ribs that curve around the sides of the torso, extending from their posterior attachments at the spine to their anterior connections.
The ribs change in curvature and length from top to bottom. The uppermost ribs are shorter and more sharply curved, while those in the middle are longer and less curved. This arrangement creates an enclosed space, the thoracic cavity, which tapers superiorly and expands inferiorly.
Built for Protection
The bony framework of the rib cage provides a protective enclosure for internal organs. It guards the heart and lungs within the chest cavity. This framework also protects major blood vessels, such as the aorta.
The combination of rigid bones and flexible cartilage enables the rib cage to absorb impacts. The presence of costal cartilage allows for yielding, helping to dissipate forces from external trauma. This design minimizes direct damage to the underlying organs during impacts.
Movement for Respiration
Beyond its protective role, the rib cage is designed to facilitate breathing. It is a flexible structure due to the articulating joints and the costal cartilages. This flexibility allows the rib cage to expand and contract, which is essential for respiration.
During inhalation, muscles such as the diaphragm and external intercostals contract. The external intercostal muscles pull the ribs upward and outward, increasing the thoracic cavity volume. This expansion creates a pressure difference that draws air into the lungs. During exhalation, the diaphragm relaxes, and internal intercostal muscles may contract to pull the ribs downward and inward, reducing chest cavity volume and expelling air. This coordinated movement is important for efficient lung function.