Hows it going Neuro Midterm 2 .docx

Hows it going Neuro Midterm 2 .docx - Chapter 5 Hows It...

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Chapter 5 How’s It Going? 5.1 Name the parts of a growth cone: Lamellipodium: The sheetlike extensions of membrane produced by growth cones Filopodia: The slender, rodlike extensions of membrane produced by growth cones How do growth cones advance? Extending itself out, latching onto some adhesive portion of the environment, then contracting to pull the rest of the structure forward. Actin (protein) provides the force to push the tips of filopodia out and pull them back in. The filopodia kind of ‘sniffs’ the environment, follows guidance cues and leaves a ‘tail of an assembled axon. How are microtubules assembled & what functions do they serve? Molecules of the protein tubulin assemble to form the microtubules that provide a sleek structural core to the axon, as well as a scaffold for extensive axonal transport (where additional building components are brought from their manufacturing site in the cell body to the growth cone - anterograde transport - and chemical messages are sent from the growth cone back to the cell body - retrograde transport). 5.2 What is the role of adhesivity in the movement of growth cones? For growth cones to advance, filopodia must have something to adhere to, if not they make little progress by themselves. However, adherence is not considered a required factor for axonal pathfinding. What is the disadvantage for the function of a growth cone if a surface is too adhesive? There needs to be the right degree of adhesity, if there is too much it can impede growth as it has difficulties dislodging lamellopodia to move the cone forwards. RESEARCHERS AT WORK - Example “Getting a grip: The role of Adhesion in Axonal Growth” Hypothesis : Growth cones in a dish will preferentially grow along whichever pathway they find most adhesive. Results : Found no correlation Conclusion : Adhesive surfaces are definitely required, but there is a fine line between not sticky enough and too sticky. If the surface is too sticky, it can impede growth, because it is hard to move the whole growth cone forward. The researchers concluded that differences in adhesion might play a permissive role (allowing particular growth cones to grow along particular pathways), but not an intrusive role (directing growth cones in a particular direction or to choose a particular pathway among several alternatives) 5.3 What are the two main types of cues that guide growth cones? Short range cues: direct contact with membranes of other cells. The ligand embedded in the membrane of one cell engages a receptor embedded in the membrane of another cell Long-range cues: diffusible molecules released by cell of group. A concentration gradient can be seen, a process known as chemotropism (‘following a chemical [trail]’) How does a filopodium respond to contact with an attractive surface versus a repulsive surface?
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