Neuro Midterm 2.docx - Neuro Midterm 2 Chapter 5 Axonal...

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Neuro Midterm 2 Chapter 5 – Axonal Pathfinding Early Portraits of Growth Cones Growth cones = at end of axons – move axons along. They find a path. Growth Cones in Culture Lamellipodium: Flat part Filopedia: Webbed fingers. Seeking out component looking for attractive or repulsive cue. o Not only the cues but axon itself to reach out to the cues Growth Cones in Action Two components: Actin and tubulin (tubules) Components of cytoskeleton – holding cell in shape to be functional End of growth cones – actin: fingers Microtubules = inside the axon. Fill cytoskeleton of the axon. Microtubule units = constructed to come out Microtubules disassemble if a repulsive force is found. Axons grow up by adding to the tip Labelled microtubules. Took one spot and used UV to bleach fluorescent label. Watched axon grow and see If bleached area = in same spot or moves along. The bleached area did not move – indicated that they add by the end. Adhesion and Growth do not Correlate Indicated there may be something sticky that the growth cones were moving towards o Coated the dish the slides were in with different amounts of stickiness. o Theorized that with increase stickiness meant more growth o Found that there was no relation between adhesion and growth rate. o First study found adhesion was not critical. But with too much adhesion they won’t grow so it is a factor. But does not directly direct growth. Growth cones Actively navigate First were poking out (actin filaments) Fine with repulsive cue they completely disassemble. With attractive signals – continue to grow in that direction (grow axon) When they change directions they collapse that side. With group of axons – some have that = pioneer o Pioneer neurons: look for and respond to cues (attractive or repulsive) The pluses indicate the axons are attached to each other. Fasciculation growth cones: follow the pioneer neurons If they all go in the wrong direction, there will be disorder. Axon guidance signals Two types of cues: Repulsive and attractive o 1. Cell associated/Contact guidance – must touch each other – contact allows cue to take place juxtracrine o 2. Diffusion molecules – axons get attracted by moving through extracellular space. long range cues diffused by cell or group of cells that forms a concentration gradient that guides growth cones paracrine Membrane-Bound Cues for contact guidance of growth cones Contact guidance o Integrin’s: have ligand outside Extracellular matrix proteins bind and provide cues for integrin’s o First three = ligand and receptor o Last one = ligand with extracellular Diffusion o Tropic = provides cues o Trophic = maintains growth o Netrin binds to frazzled – attractive o Semaphoring = repulsive
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Pioneer neurons rely on guideposts Come from peripheral to CNS Cell body extends growth cones until another set of cells. Act like guide post (set of cells) – hold on
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