ANATOMY OF THE LUMBAR SPINE

What carries the majority of your body’s weight?
What is the role of the intervertebral discs?
What is the intervertebral disc nucleus?
What is the role of the spinal canal?
What is the role of the spinal nerve roots?

The Spinal Column and the Vertebrae

Your spinal column consists of 24 separate bones, called vertebrae, plus the five fused bones of the sacrum and the four fused bones of the coccyx (often referred to as the "tail bone").

The vertebrae are stacked one on top of another and can be divided into:

• the cervical (neck) spine: the top seven vertebrae,
• the thoracic (chest) spine: the middle 12 vertebrae, and
• the lumbar (lower back) spine: the bottom five vertebrae.

Support for the Vertebral (Spinal) Column

Attached to the vertebrae are muscles, tendons and a group of strong bands, called ligaments, together, they support the spinal column and help to protect its delicate nerves.

The Role of the Vertebral (Spinal) Column
What Carries the Majority of Your Body's Weight?

Your spinal column enables you to walk upright. It is the central support for your upper body and carries the weight of your head, chest and arms. The vertebrae in the lumbar (or lower back) portion of your spine carry the majority of this weight. The constant pressure from this weight, even when you are simply sitting in a chair, is what usually leads to problems associated with the lower back.

The Role of the Intervertebral Discs

The bony vertebrae of your spinal column are separated from one another by "pads" of tough cartilage, called intervertebral disk.

These discs act like "shock absorbers" during activity, allowing the spine to move freely. How a disc "ruptures" (bulges outward) is shown in the drawing in Figure 2 and will be discussed in detail on the following pages.

The Intervertebral Disc Nucleus

The center of each intervertebral disc is made up of a gelatin-like substance (the nucleus), surrounded by a fiber-like outer lining (the annulus).

As your body ages, the disc’s nucleus begins to stiffen. This reduces flexibility and increases the chances that a disc may "rupture," especially in the lumbar spine which carries so much of your body’s weight.

The Spinal Canal

The spinal cord, which begins at the base of the brain and runs within the spinal canal, ends in the lumbar spine area in a bundle of nerves known as the cauda equina (Figs. 3 & 4). The spinal canal runs through the center of the spinal column and protects the spinal cord and other delicate spinal nerves.

The Spinal Nerve Roots

At each vertebral level, a pair of nerves branch off from the spinal cord or the cauda equina (one to the left and one to the right). These spinal nerve roots are part of the body’s "electrical" system, carrying "current" (for sensation and movement) to specific parts of the body.

The nerve roots are protected by an "insulated" covering in the same way a "live" electrical line is coated to prevent direct contact with the bare wire. A nerve root damaged by a ruptured disc may have all or part of its "insulation" rubbed off at the point of injury. Prior to surgery there is no way of telling how much has been rubbed off or how much damage has been done to the nerve (the body’s "live electrical wire").

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