Rib

From ArticleWorld

A rib is a slender, curved bone that is one of 24 similar bones that surround the thorax and provide structure and protection to the lungs and other thoracic organs.

Anatomy

Ribs are generally paired with an identical rib on the other side of the thorax. In most people, there are twelve pairs of ribs; however, a small number of people can have more or less than twelve pairs. They are somewhat flattened, slender and generally curved to shape the thorax. No two ribs are alike. In most cases, only ten pairs of ribs actually have connections to both the back and the front of the thorax.

The third through ninth ribs are similar and can be called “usual” ribs. At the furthest posterior aspect of each rib are two points of articulation. The lower one attaches to the transverse process of its identically numbered thoracic vertebra while the upper articulation is with the underside of the vertebra above it. As one moves outward the shaft of the rib flattens out and curves around to the front of the body. The “typical” rib gives way to a cartilaginous portion that can be several centimeters in length.

The rib pairs one through seven all attach via the cartilaginous portion to the sternum so that they form a complete circular cage around the thorax. The 8th through the 10th ribs come together in the front and connect into a single cartilaginous portion which then connects to the cartilage of the seventh rib. These three ribs are sometimes called “false ribs”. The last two rib pairs articulate in the back but end as shorter stubs of the others. They are known as “floating ribs.”

Function

The ribs together protect the heart and lungs from moderate trauma. The lower ribs (8th through the 10th) also form some protection for the liver and the spleen. Between the ribs are multiple bands of muscles called the intercostal muscles. While the diaphragm forms the main breathing muscles, the intercostal muscles help to expand and contract the chest in breathing. For this reason, they are called accessory breathing muscles.

The ribs also provide protection for the muscles and nerves of the outer thorax. The typical ribs have a groove on the inner, lower aspect that is the route of travel for the intercostal blood vessels and the intercostal nerves.

Conditions

The ribs are somewhat elastic as a group but can still be fractured upon being traumatized. The most common area of fracture is in the lateral and posterior areas. If severe, a rib fracture can result in a punctured lung. In addition, an individual can be born with an extra cervical rib which may affect the passage of nerves and blood vessels to the arms.