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The spine is made up of a series of interconnecting bones called vertebrae (an individual unit is called a vertebra). The vertebral column (spine) is the main support structure for the body and keeps it upright and balanced. Other functions of the spine include:

• Providing platforms for attachments of many muscles and ligaments that traverse the skull, the thorax, and the pelvis
• Permitting the trunk of the body to have appreciable flexibility of movement, such as twisting, bending, or arching the back
• Protecting the spinal cord while providing openings between adjacent vertebrae for the passage of spinal nerves

The spinal column consists of 33 bones and is divided into:

• 7 cervical vertebrae which form the upper part of the spine between the skull and the chest
• 12 thoracic vertebrae which are found between the upper chest and lower back
• 5 lumbar vertebrae which form the lower back and are the largest and strongest of the vertebrae. They are the source of attachment of many strong back muscles.
• 5 vertebrae fused together form the sacrum, which is triangular in shape and connects the spine to the pelvis. The sacrum also provides support for the spine.
• 4 fused vertebrae form the coccyx ("tail bone") which has little known function

The vertebrae are connected much like the links of a chain. Although there are differences of function among the vertebrae of the various regions of the spinal column, there is a basic design common to all of them.

A typical vertebra is comprised of several components, including:

• Vertebral body - main anterior bony part of the vertebra. It faces the front of the body (anterior) and is the weight-bearing segment of the vertebra. It is cylindrical in shape.
• Centrum - the thick anterior portion of the vertebra. It is the largest part of the vertebra.
• Pedicles - two short stalks that project off of the right and left sides of each vertebral body and function as attachment sites for muscles and ligaments of the spine. They also make up the sides of the neural arch.
• Laminae- flat bones that arise from the posterior part of the vertebra. They form the roof of the spinal canal and protect the spinal cord.
• Vertebral (neural) arch - arises from the posterior surface of the centrum and forms a circle of bone around the canal through which the spinal cord passes. A vertebral arch is composed of a floor at the back of the vertebra, walls (the pedicles), and a roof where two laminae join.
• Vertebral foramen (also called the spinal canal) - opening formed by the (anterior) centrum, and the (posterior) vertebral arch. It is an enclosed space through which the spinal cord passes.

• Processes - bony projections from the back of the vertebra that function as important attachment sites for spinal muscles and ligaments. There are three processes, namely:

  • spinous process - a projection from the posterior, midline region of the neural arch (these projections are the bumps you feel when you run your hand down the spine)
  • superior and inferior articulating processes - there is a pair of each of these processes on each side of the neural arch. The superior processes project upward and the inferior project downward. Each articulating process has a smooth surface that interlocks and forms a facet joint between the vertebra above and below it which facilitates movement of the spine and also increases the rigidity of the vertebral column.