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Understanding Spinal Anatomy: Vertebral Structures
The outer shell of a vertebra is made of cortical bone. Cortical bone is dense, solid and strong. Inside each vertebra is cancellous bone, which is weaker than cortical bone and consists of loosely knit structures that resemble honeycomb. Bone marrow, which forms red blood cells and some types of white blood cells, is found within the cavities of cancellous bone. Vertebrae consist of the following common elements:
Vertebral Body: The largest part of a vertebra. If looked at from above, it generally has a somewhat oval shape. When looked at from the side, the vertebral body is shaped like an hourglass; thicker at the ends and thinner in the middle. The body is covered with strong cortical bone, with cancellous bone within.
Pedicles: These are two short processes, made of strong cortical bone, that protrude from the back of the vertebral body.
Laminae: Two relatively flat plates of bone that extend from the pedicles on either side and join in the midline.
Processes: There are three types of processes: articular, transverse and spinous. The processes serve as connection points for ligaments and tendons.
Four articular processes join with the articular processes of adjacent vertebrae to form the facet joints. The facet joints, combined with the intervertebral discs, allow for motion in the spine.
Spinous processes extend posteriorly from vertebrae where the two laminae join, and act as a lever to effect vertebral motion.
Endplates: The top (superior) and bottom (inferior) of each vertebral body is coated with an endplate. Endplates are complex structures that blend into the intervertebral disc and help support the disc.
Intervertebral Foramen: The pedicles have a small notch on their upper surface and a deep notch on their bottom surface. When the vertebrae are stacked on top of each other the pedicle notches form an area called the intervertebral foramen. This area is of critical importance, as the nerve roots exit from the spinal cord through these areas to the rest of the body.
Facet Joints: The joints in the spinal column are located posterior to the vertebral body (on the backside). These joints help the spine to bend, twist, and extend in different directions. Although these joints enable movement, they also restrict excessive movement such as hyperextension and hyperflexion (i.e. whiplash).
Each vertebra has two facet joints. The superior articular facet faces upward and works like a hinge with the inferior articular facet (below).
Like other joints in the body, each facet joint is surrounded by a capsule of connective tissue and produces synovial fluid to nourish and lubricate the joint. The surfaces of the joint are coated with cartilage that helps each joint to move (articulate) smoothly.
