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5e concept of nerve injury (common causes of nerve injury (2.crushing, 3…
5e
concept of nerve injury
common causes
of nerve injury
2.crushing
3.injection of toxic substance
into the nerve
4,Ischemia
(interference in the blood supply)
5.Hyperpyrexia
(incr in body temp beyond
40.5 deg C/105 F
1.transection(through & through cut)
grading of injury
by Sunderland
1st degree injuries
Most commonly seen
secoundary to ischemia
-caused by
direct pressure to a nerve
for a limited time
ischemia- produces
local anoxia(complete lack of O2)
with temporary imparement
of nerve function
it gets corrected
-within a few hours to few weeks
cos the axon is not destroyed
but merely lost its functional properties
for a short time
2nd degree injuries
prolonged & or severe pressure
damages the nerve fibers
at the pressure point
eventually causing death of axon
locally & distally
3rd degree injuries
endoneural tubes becoming
interupted
4th degree injuries
fascicles becoming disorganized
5th degree injuries
through & through cutting of
nerve fibers( complete transection)
degenerative changes
1.Retrograde changes
(changes in nerve cellbody
changes begin within 48hrs
of nerve section
& reach to a max by 15-20 days
1.chromatolysis
nissle granules disintegrate
(break up into fine dust)
-& loose their staining rxn after
15-20 days
-& cell becomes colourless
the process begins in
the zone around the nucleus
& spread to the periphery of the cell
the dissolution of nissle substance(RNA)
occurs so that the
protein manufacturing process
can be mobilized to help
the neurons to survive
2.
golgi apparatus
mitochondria
& neurofibrils
-fragmented &
gradually dissapear
3.
cell draws more fluid
loses its polygonal shape
& becomes round
4.
nucleus
incr in size
is displaced to the periphery
& becomes oval
it may be completely thrown
out of the cell,then the cell atrophies
& finally dies off
degree of damage
& chromatolysis
depends upon
1.the variety of neurons effected
in the PNS
-changes as described above
will occure
in the CNS
-no regeneration of nerve cells
takes place
cos it has no centrosomes
in the ANS
-changes are difficult to
demostrate
due to the
normal sparesness of
nissle granules
2.the distance of
lesion frm the nerve cell
if the distance is less
more damage occurs
3. nature of injury
if its a sharp cut
-the effects would be less
if its forcibly torn
-death of the cell occurs
2.changes to the
distal stump