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The spinal cord originates in the brain, exiting
through a hole at the skull base called the foramen magnum and coursing
through the spinal canal of the cervical, thoracic and upper lumbar
spine before ending most commonly between the first and second lumbar
vertebrae.
Nerve roots exiting from the lower end of the
spinal cord continue as a structure called the cauda equina, or horse's
tail, to provide nerves to the lower trunk, legs, bowels, bladder and
sexual organs.
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Several protective membranes
cover the spinal cord. The outermost layer (dura mater) forms a
tough tube that encases the two inner membranes (arachnoid and
pia mater) and contains spinal fluid, commonly called
cerebrospinal fluid (CSF). This fluid cushions, protects and
nourishes the spinal cord and nerve roots. Enough cerebrospinal
fluid to fill a soft drink can (about 350 cubic centimeters) is
reabsorbed and replenished daily.
The spinal cord itself is
a large, nearly circular mass of nerve tissue. It carries
messages from the brain to the rest of the body. It also carries
messages or sensations from the rest of the body to the brain.
The spinal cord gives off branches or paired nerve roots at each
level of the spine, except the top cervical vertebrae. These
roots leave the spine on both sides through spaces (neural
foramina) between each vertebra.
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Damage to the nerves can cause pain, tingling,
numbness or weakness in the area where the
nerve travels. Damage to the spinal cord at any
level can cause many symptoms, from paralysis to numbness.
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