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Definition
| Growth cones can travel along tracts of axons (fascicles) but to reach target, they much "get off" of this tract. |
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Term
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Definition
In Drosophila, these two genes influence a neurites ability to defasiculate.
Beat-1a is an anti-adhesion factor secreted by the growth cone that helps the axon become "unsticky"
Beat-2c is a cell membrane protein that has pro-adhesive function
(e.g. if beat-1a is mutated, then defasiculation can't occur. if both are mutated, then neurite behaves normally again since can't fully adhese so it doesn't matter if it can't produce the anti-adhesive. |
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Term
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Definition
| Sialic Acid decreases the adhesion of NCAMs, making an effective mechansim through which to manage the defasiculation process. |
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Term
| Neurotrophins and Receptors |
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Definition
Diffusable molecules that encourage the survival of neurons... emmitted by targets.
Cells can swuitch their preference for given neurotrophic factors and can encourage defasciculation
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Term
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Definition
Decreased levels of Fibroblast Growth Factor could be used as a cue for growth cone to slow down once within target region.
(if exogenous FGF applied, axon keeps on grown past region) |
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Definition
Ephrin is a repulsive protein that prevents axons from leaving target region. It also forms bariers to keep axons from projecting into incorrect areas. |
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Term
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Definition
| FGF is a factor whose decrease in the optic tectum is associated with slowing down of the growth cone once it reaches its target |
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Definition
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Term
| Repulsion Cues/Topographic mapping |
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Definition
| Repulsive cues (such as Ephrins) can be used in gradients to determine where the axons will project. Dependent of level of ephrin receptors, a given axon will very in sensitivity of ephrin and therefore project deeper or closer. Thus ephrin gradients can help set up topographic maps which are neural layout of sensory/motor processing. |
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Term
| Steps invovled in target selection |
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Definition
Defasciculation
entering target area
slwo-down
search for psotsynaptic partner
branch out in target area
arrive at correc coordinates
select specific cell or dendrite target
refine connection |
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