STRUCTURE OF THE VERTEBRAE AND DISC

 

THE VERTEBRAE 

         The main part of a vertebra is more or less cylindrical, with a flat surface at the top and bottom, and a small hole running vertically through each, toward the back edge. When your vertebrae are aligned, these form a channel—the spinal or neural canal—that contains and protects your spinal cord. 

         

    The back of each vertebra has seven projections, which are called processes. These are arranged in three pairs with an odd one out—the spinous process. Your spinous processes are the knobbly bits that run all the way down your spine. The spinous process sits between the six paired processes (three on either side). 

    Two of the pairs—the upper articular processes and the lower articular processes—act as joints, linking your vertebrae and strengthening your spine. Your back muscles are attached to the remaining pair, the transverse processes, and also to the spinous process, all of which provide anchorage as your muscles contract and relax

     No two vertebrae are exactly alike. Although they fit together perfectly, they all have individual characteristics

    The lowest two thoracic vertebrae, which have small flat facets (costal facets) where they are attached to the ribs, 

THE FACET JOINTS

      Each of the vertebrae in spinal column meets at a facet joint. It is here that the lower articular processes of the first vertebra link up or articulate with the upper articular processes of the second. The surfaces of these processes are smooth and flat, —hence the reason that the joints are called facet joints, also known as posterior joints

THE DISCS

     

          The flat surfaces at the top and bottom of the main body of your vertebrae are covered in a thin layer of cartilage known as an end plate. An intervertebral disc (or intervertebral fibrocartilage) lies between adjacent vertebrae in the vertebral column, separating each vertebra in your spinal column from the vertebrae above and below it, enabling you to move and twist your body.

       The outer layers of this disc are made up of bands of tough fibrous cartilage, which form  the annulus fibrosus. The annulus fibrosus then blends with the end plate cartilage, which coats the flat surfaces of each vertebra. 

       Inside the annulus fibrosus, filling the center of the disc, is a pulpy gelatinous substance known as the nucleus pulposus— allows the disc to mold and reshape itself like a liquid ball bearing. This means that, in addition to acting as a joint, the disc  also play essential role as a shock-absorbing cushion between each vertebra. A healthy disc is extremely strong—much stronger, in fact, than a vertebra. This great strength means that a disc is capable of absorbing considerable forces, or shocks. The disc is also able to absorb compressive and jarring forces with a high degree of efficiency because it can adapt its shape, distributing the strain across its surface more evenly.

      However, discs are more vulnerable to stresses that are caused by twisting motions—in extreme cases, such movements can cause the outer layers of the disc to rupture. The annulus fibrosus contains a number of pain-sensitive nerves and the pain associated with a “slipped disc”— a misnomer, since a disc cannot slip, but can herniate or rupture—often due to the result of an injured disc pressing on the Dural sheath or a nerve, or even from a tear in the fibers of the annulus fibrosus itself