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") (Fig. 1). 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
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 Invertebral Discs
The
bony vertebrae of your spinal column are separated
from one another by pads of tough cartilage, called intervertebral
discs (Fig. 2,above). These discs act
like shock absorbers during activity, preventing
the individual vertebra from rubbing against one
another. Healthy discs, with their gelatin-like inner
core, allow the spine to move freely and provide
much of the flexibility found in a young person's
spine.
The
Invertebral Disc Nucleus
The
gelatin-like center of each intervertebral disc (called
the nucleus) is surrounded by a tougher, fiber-like
outer lining (called the annulus) (Fig. 3).
As your body ages, the disc's nucleus begins to "dry
up" and stiffen, increasing the chances that the
central bundle of nerves and/or a spinal nerve may
eventually become pinched.
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 (Fig. 3,above).
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 and the Foramen
At
each vertebral level, a pair of spinal nerve roots branch
off from the spinal cord or the cauda equina (Fig
3,above) and pass through an opening in the vertebra
called the foramen (Figs. 3,above & 4). "Plump" and
healthy discs help to cushion the vertebra and keep
the opening of the foramen wide enough for the spinal
nerve roots to pass through without being pinched.
The
Body's "Electrical" System
The spinal
nerve roots are part of the body's "electrical" system,
carrying "current" (for sensation and movement)
to specific parts of the body. These nerves are
protected by an "insulated" covering in the same
way a "live" electrical line is coated to prevent
contact with the bare wire. When a nerve root is
damaged, all or part of its protective coating
may be rubbed off at the point of injury. Prior
to surgery there is no way of telling how much
of this "insulation" has been rubbed off or how
much damage has been done to the nerve itself (the
body's "live electrical wire").
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