Spinal Anatomy
The spinal column consists of 24 separate bones, called vertebrae,
plus the fused bones of the sacrum and the coccyx. Your spinal column
is the central support for the upper body, carrying most of the
weight of your head, chest, and arms. Together with the muscles
and ligaments of your back, your spinal column enables you to walk
upright.
The cervical region has seven vertebrae (C1 through C7), the thoracic
region has 12 vertebrae (T1 through T12) and the lumbar region has
five vertebrae (L1 through L5). The sacral region consists of five
vertebrae, all fused together to form one continuous bone mass known
as the sacrum. The coccygeal region consists of four vertebrae,
all fused together to form the coccyx or tailbone.
The vertebrae in the cervical (or upper back) portion of your spine carry
the weight of your head. The pressure from this weight along with the "wear
and tear" associated with the constant turning and bending of your head and
neck is what usually leads to problems associated with the cervical vertebrae.
The vertebrae in the lumbar (or lower back) portion of your spine are under
constant pressure from the weight of your upper body, even when you are simply
sitting in a chair. The "wear and tear" of this pressure is what usually leads
to problems associated with the lower back.
The intervertebral discs are composed of a fiber-like outer lining (the annulus)
and a gelatin-like inner core (the nucleus). These discs act as the spine's
"shock absorbers," preventing vertebra from rubbing against one another and
providing much of the flexibility found in your spine. Because they are under
constant pressure, it is the intervertebral discs which first show signs of
the "wear and tear" associated with the aging process.
Running through the center of the spinal column is the spinal cord, which
ends in the lumbar spine in a bundle of nerves called the cauda equina. At
each disc level, a pair of spinal nerve roots branch off from the spinal cord
or cauda equina and pass through an opening called the foramen.
As your spine ages, the gelatin-like centers of your discs begin
to dry out, thereby reducing their effectiveness as "shock absorbers."
As this protection is lost, the simple "wear and tear" of everyday
activity can cause the bone matter of your vertebrae to develop
jagged edges, called bone spurs. As these spurs develop and extend
outward, they can cause both the spinal canal and the foramen to
become narrowed. The result is often the pinching (compression)
of the spinal cord and/or a spinal nerve root.
As discs dry out, your vertebrae begin to "settle." This "settling"
causes the window-like openings of the foramen and the spinal canal
to become smaller and smaller. Eventually, these openings can become
so small that a spinal nerve(s) becomes "pinched" against a vertebra.
It's similar to slowly closing a window on your hand. There will
be a point at which you begin to feel the pressure. The more the
window is closed, the greater the pressure and the greater the pain.
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The Growth of Bone Spurs