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5e1 degenerative changes in neurons (1.Retrograde changes (changes in…
5e1
degenerative changes in neurons
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
it undergoes complete degeration
the process starts within 24hrs of injury
changes in the AP can be observed
as early as 2 days after section
after the 3rd day,
-ability of the nerve to conduct an impulse
decreases markedly
after the 5th day
-impulse can no longer be evoked
the cahnges are:
1.Axis cylinder
breaks up into short lengths
& after a few days little debris
(dust like particles)
are left in the space formerly
occupied by the axon
2.myelin sheath
breaks up more slowly
than axon
into small oily droplets
its destruction occurs in
2 stages
physical destruction
up to 8-10 days
little or no change in
histochemistry of
oily droplets is seen
chemical destruction
starts on 8th day &
goes on until 32nd day
is caused by enzymes of Schwann cells
or macrophages lining the endoneurial tubes
3.nucleus of schwann cells
starts multiplying mitotically
with formation of cord cells
which fill up the endoneurial tubes
4.macrophages
frm endoneurium start digesting
(phagocytosing) debris of
axis cylinder & myelin sheath
once the debri are cleared
schwann cell cytoplasm starts proliferating
& fills up the endoneurial tubes
-this process takes 3mnths
ultimately
all thats left of the fibers are the neuroleminal tubes
enclosing a mass of granular cytoplasm containing
many nuclei
3.changes at the
site of injury
schwann cells differenciate
into thin elongated cells,
mainly frm the distal end
& very little frm the proximal end
they can bridge up the gap
upto 3cms
rate of progress of growth is
1=2 mm/day
if gap is more than 3cm
-its diffc to fill up
cos of interlacing of fibers
this can be facilitated by
operating procedures
-by removing the debris & stiching
the 2 cut ends together
-for an early degeneration & regeneration