There is a logical and physical topographical
organization to the anatomy of the central nervous system, which is
an elaborate web of closely connected neural pathways. This ordered
relationship means that different segmental levels of the cord
control different things and injury to a particular part of the cord
will impact neighboring parts of the body.
The most common causes of
damage to the spinal cord (Paraplegia or Quadraplegia) are trauma's
such as motor vehicle accidents, motor bike accidents, falls, sports
injuries (particularly diving into shallow waters), gunshot wounds,
assault and other injuries; and disease such as poliomyelitis and
spina bifida.
Direct injury such as cuts
can occur to the spinal cord, particularly if the bones (vertebrae)
are damaged. Fragments of bone or fragments of metal (for example
from a car accident) can cut or damage the spinal cord causing
injury. If the head, neck or back are twisted abnormally, the
spinal cord can be pulled, compressed or pressed sideways, also
possibly causing direct damage. The accumulation of blood or fluid
can cause swelling within the spine or spinal cord causing
compression of, and damage to the spinal cord, resulting in an
spinal cord injury.
A common set of biological events take place
following spinal cord injury:
Cells from the immune system migrate to the
injury site, causing additional damage to some neurons, and death to
others, that survived the initial trauma.
The death of oligodendrocytes causes axons to
lose their myelination, which greatly impairs the conduction of
action potential messages or renders the remaining connections
useless. The neuronal information highway is further disrupted
because many axons are severed, cutting off the lines of
communication between the brain and muscles and between the body's
sensory systems and the brain.
Within several weeks of the initial injury, the
area of tissue damage has been cleared away by microglia and a
fluid-filled cavity surrounded by a glial scar is left behind.
Molecules that inhibit regrowth of severed axons are now expressed
at this site. The cavitation is called a syrinx, which acts as a
barrier to the reconnection of the two sides of the damaged spinal
cord.
Although spinal cord injury causes complex
damage, a surprising amount of the basic circuitry to control
movement and process information can remain intact. This is because
the spinal cord is arranged in layers of circuitry. Many of the
connections and neuronal cell bodies forming this circuitry above
and below the site of injury survive the trauma.
The spinal cord runs down the back, protected
inside a body case (Vertebrae.. The spinal cord contains bundles of
nerve fibres which connect the brain with the skin, organs and parts
of the body. It acts like a telephone line that relays messages from
your brain (telephone switchboard) via the spinal cord (telephone
cable) to all parts of your body (telephone receivers) and back
again.
For example, when you want your toe to move, the
message "toe move" is relayed down the cord, through the nerve of
the toe, and your toe moves. At almost the same time, the toes sends
back the message "I've moved" to the brain. In Paraplegia and
Quadriplegia, the spinal cord is damaged so the message cannot be
sent to areas below the damaged area, or back again.
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