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18 Cards in this Set
- Front
- Back
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What is the response when the site of damage is: dendrites and synapses neuronal cell body axon and target innervation |
Dendrite and synapses: loss of these can be restored by regrowth/plasticity Neuronal cell body: neurons are postmitotic and cannot divide to replace cell, neural stem cell differentiation to replace is possible Axon and target innervation: CNS axon regrowth is inhibited, PNS axon regrowth is possible |
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Summary of axon regeneration |
1. Axonal injury stimulates the regenerative response from soma (retrograde transport of positive signals from stump) 2. Wallerian degeneration (proximal axon degenerates to most proximal node of Ranvier) 3. Regeneration of proximal axon (axon guidance path, remyelination and re-innervation) |
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Anterograde transport of material along the microtubule cytoskeleton goes where and what motor protein involved? |
To the nerve terminal, vesicle is coupled to kinesin. |
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Retrograde transport of material goes where and what motor protein is involved? |
Goes away from the nerve terminal, vesicle is coupled to dynein. |
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Materials that are involved in anterograde transport? |
Neurotransmitters and structural proteins. |
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Materials involved in retrograde transport. |
Viruses Debris Growth factors (nerve growth factor [NGF] and brain derived nerve factor [BDNF]) |
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What is important in establishing the pathway in axonal growth? |
Cytoskeleton reacts to attractive and repulsive signals on or secreted by tissues in growth pathway. Pioneer growth cones establish pathway. Growth cones/filopodia are important active elements. |
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3 different types of guidance signals for axon regrowth |
1. Adhesive substrate-bound cues (roadway) 2. Repellent substrate-bound cues (roadway guard rails) 3. Diffusible chemotropic cues (road signs) |
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What wraps each structure? Nerve Individual fascicle Axon
What are groups of axons bathed in?
What is the fatty material between fascicles? |
Epineurium Perineurium Endoneurium
Endoneurial fluid
Interfascicular epineurium |
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What triggers Wallerian degeneration? |
Severe nerve injury (trauma, transection, toxins, inflammation, demyelination) OR Axonal transport blockade |
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What happens in the neuron soma and proximal axon in Wallerian degeneration? |
Protein aggregation in the neuronal soma Proximal axon kept from degenerating by NGF and BDNF Macrophages invade site of injury and secrete cytokines Schwann cells secrete extracellular protein (laminins, CAMs and NGF) Proximal axon sprouts within 96 hours |
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What happens in the distal axon in Wallerian degeneration? |
Degeneration over 1-2 weeks Glial cells push synaptic terminal away from muscle Demyelination of axon Schwann cell phagocytoses debris Schwann cells and endoneural tubes act as support guides for 1-2 months |
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Main diagnostic tool for peripheral nerve demyelination? |
Electrophysiology. Important to stimulate and record at several different levels/distances to localise site of damage. |
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Outcome for axon and nerve intact but nerve conduction block |
Good prognosis, 3-4 months recovery |
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Outcome for axonal damage but nerve intact |
Good prognosis, axon growth at ~1mm per day from injury to the tissue target |
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Outcome for axonal and nerve damage |
Variable prognosis. Requires nerves to be reconnected (e.g. nerve suturing) for axon guidance and regrowth, up to 18 months recovery period.
Nerve grafts and conduits good for overcoming large gaps. |
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4 aids to peripheral nerve repair |
1. Fibrin tissue glue (provides ECM around nerve approximation) 2. Nerve graft (isograft vs allograft) 3. Nerve conduit (guidance, prevent axonal escape and scar tissue invasion, rich in NGF, materials include collagen, PGA and polycaprolactone) 4. Electrical stimulation |
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3 sources of stem cells |
1. Embryonic stem cells (pluripotent) 2. Induced transformation of tissue stem cells (reversion from adult cells) 3. Adult brain has sites with stem cells (usually multipotent) |
