Plasticity and regeneration in the Nervous system Flashcards
Axotomy
is the cutting or otherwise severing of an axon
Wallerian or anterograde degeneration
-the degeneration of the distal end an axon of the PNS and its myelin sheath when it undergoes axotomy
What cells will clear the degenerating axons and myelin sheath of a nerve who underwent anterograde degeneration
tissue macrophages
Schwann cells stay in the damaged area undergo mitosis and proliferation
promoted by
macrophages
Schwann cells recruited and influenced by macrophages will do what to a PNS neuron that underwent an axotomy
The Schwann cells will form a column that connects the cut end of
the axon with the original target. This column will be important for guiding a regenerating
axon back to its appropriate target.
The proximal end of the axon will also die back by ___degeneration,
retrograde
In early stages of regeneration, the cell will exhibit chromatolysis. Define chromatolysis
disruption of Nissl bodies
Nissl bodies
These granules are of rough endoplasmic reticulum (RER) with rosettes of free ribosomes, and are the site of protein synthesis. It was named after Franz Nissl, a German neuropathologist who invented the Nissl staining method.
In early stages of regeneration, the cell will exhibit ___ and ___
chromatolysis and eccentric relocation of the nucleus.
bouton shedding
presynaptic inputs to axotomzed neurons disconnect and withdrawal
- shedding of inputs
- helped by glia; they insert themselves and peel of synapses
Transneuronal degeneration
anterograde (innervated neuron dies) or retrograde direction (innervating neuron dies).
if regenerated axons are able to reach their target, are they remyelinated?
yes
-Determination of the extent of myelination is made by the characteristics of the axon and not the Schwann cell
Collateral and paraterminal sprouts originate from ____ or _____, respectively, and are stimulated by factors released from the ____
- nodes of Ranvier (collateral) or axon terminals (paraterminal)
- stimulated by factors released from denervated tissue
What findings suggest that axotomy removes a retrogradely transported neutropic signal derived from the target?
-Collateral sprouting can be induced in motor neurons simply by inactivating the target muscle
-Conversely, sprouting following damage in adjacent axons can be blocked by electrically
stimulating the target muscle.
After axotomy, local application of NGF to the soma
can ___ chromatolysis and bouton shedding.
-prevent
Administration of the microtubule poison colchicine
can also ____chromatolysis and bouton shedding.
induce
colchicine
-microtubule poison that can induce chromatolysis and bouton shedding
The best known of these myelin-associated growth inhibitors is ___
-Nogo-A.
laminin and fibronectin
-growth factors that are found in the PNS and CNS extracellular matrix during development, but only in the PNS in adulthood
oligodendrocytes in the CNS synthesize glycoproteins that ____
-suppress axon outgrowth
what did Aguayo et al. show about regeneration of the optic nerve?
-the optic nerve was transected near the eye and they
demonstrated that the axons of retinal ganglion cells would not grow through a resected
optic nerve
-However, they would regenerate through a Schwann cell column from a peripheral nerve graft
-Regenerated retinal ganglion cell axons grew through the graft and innervated the superior colliculus, a normal target.
failure to show regeneration in the CNS is a property of the____
- supporting cells and not the neurons
what cells were injected in an area of axotomy that actually improved recovery and even facilitated walking in a paraplegic patient
olfactory ensheathing cells
what are some areas where adult neurogenesis has been observed?
- olfactory epithelium/ bulb
- hippocampus- (especially -dentate gyrus)
- caudate nucleus
what would be the consequences of no neurogenesis
-the DG either has to encode new information at the expense of old
information or face saturation.
Occasional spontaneous cell loss is often
followed by _____and
reactive _____ from surviving
local axons.
collateral sprouting and synaptogenesis
Jon Kaas showed that somatotopic maps are
Somatotopic maps are
modifiable by experience
Synapse strengthening
probablyaccounts for earlyreorganization, implying that weak connections
exist that are not readily apparent in physiological recordings. These weaker connections can be
revealed when the dominant pathways are inactivated (or lost).
phantom limb sensations
-patients who have lost a hand experience cortical expansion of the
intact afferent pathways that normally terminate in areas surrounding the hand representation
(face, shoulder, and upper torso).
remapping of referred sensations.
cortical expansion of the
intact afferent pathways that normally terminate in areas surrounding the lost limb
