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The adult spine is made up of approximately 24 bones (vertebrae) stacked on top of each other from the bottom of the skull to the pelvis. Each vertebra is composed of several parts that act as a whole to surround and protect the spinal cord and nerves, provide structure to the body and enable to fluid movement in many planes.
The vertebral body is the main portion of the vertebra. It bears about 80% of the load while standing and provides an attachment for the discs between the vertebrae. The front or anterior section of the vertebral body protects the spinal cord and nerve roots. Both the vertebral body and the discs increase in size from the head to the sacrum.
Each vertebra has two cylinder-shaped projections (pedicles) of hard bone that stick out from the back part of the vertebral body, providing side protection for the spinal cord and nerves. The pedicles also serve as a bridge, joining the front and back parts of the vertebra.
The lamina is is the roof of the spinal canal that provides support and protection for the backside of the spinal cord.
The bumps that can be felt down the back are the spinous processes. They are bony projections that arise at right angles (perpendicular) to the midline of the lamina. Each spinous process is attached to the spinous process above and below it by ligaments. Sometimes these processes are absent or bifid in the cervical spine.
The transverse processes are located at right angles to the junction of pedicles and the lamina. They provide a place for the back muscles to attach to the spine.
For the most part, these are absent in the vertebra of the neck (the cervical spine). If present in the cervical spine they occur at the lowest level (C7) and are called a cervical rib. They may impair exiting nerve roots and cause pain.
The spinal canal is a bony tunnel surrounding the spinal cord. It is made up of the front (anterior) of the vertebral body, the pedicles on the sides of the vertebral body and the lamina in the back. In the lower back it not only contains the spinal cord, it also contains the nerve roots of the lower spine.
Each vertebra has a paired joint on its right side and a second paired joint on its left side, allowing a connection with the vertebrae above and below it. The pair that faces upward is the superior articular facet. The pair that faces downward is the inferior articular facet. The facet complex is surrounded by a watertight synovial capsule, much like the small joints in the fingers that allow for smooth movement.