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In between each vertebral body is a "cushion" called an intervertebral
disc. Each disc absorbs the stress and shock the body incurs during
movement and prevents the vertebrae from grinding against one another.
Each disc is made up of two parts: the annulus fibrosis and the
nucleus pulposus.
Annulus Fibrosus
The annulus is a sturdy tire-like structure that encases a gel-like
center, the nucleus pulposus. The annulus enhances the spine's rotational
stability and helps to resist compressive stress.
The annulus is a layered structure consisting of water and sturdy elastic
collagen fibers. The fibers are oriented at different angles horizontally
similar to the construction of a radial tire. Collagen consists of fibrous
bundles made of protein bound together by proteoglycan gel.
The intervertebral discs are the largest structures in the body without
a vascular supply. Through osmosis, each disc absorbs needed nutrients.
Nucleus Pulposus
The center portion of each intervertebral disc is a filled with a gel-like
elastic substance. Together with the annulus fibrosus, the nucleus pulposus
transmits stress and weight from vertebra to vertebra.
The structural components of the nucleus pulposus is similar to the
annulus fibrosus; water, collagen and proteoglycans. The difference is
the concentration of these substances. The nucleus contains more water
than the annulus.
Endplates
The top (superior) and bottom (inferior) of each vertebral body
is "coated" with an endplate. Endplates are complex structures
that "blend" into the intervertebral disc and help hold the disc in place.
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