lecture 9- intro to axon guidance

Question 1

what are the two theories for axon guidance

Answer 1

1= they all form random connections to each other and then the non functional ones are eliminated

2= they have ‘individual identification tags’ to direct them to the correct target

Question 2

describe the experiment used to prove axons have individual identification tags

Answer 2

removed the temporal retina and then allowed nasal axons to grow back

result= axons grew back directly in the right place, there were no extra useless connections

Question 3

what happens when the neural tube is cut out a chick embryo before axons grow and then reversed

Answer 3

the axons still ultimately guide themselves to the right muscles

Question 4

what are guidance cues

Answer 4

factors that axons contain to find their correct targets

Question 5

how can lazer experiments be used to identify axon cues

Answer 5

can lazer out cells and then see if axons still extend or whether they relied on those cells as cues

Question 6

what are the key features of the labelled pathway hypothesis

Answer 6

axons bundle together in a specific way
axons carry labels
different axon growth cones express different sets of receptors for cues
early axons form a scaffold which the later axons extend

Question 7

how do the first axons find their way

Answer 7

they follow steroetyped pathways and use normal cells

Question 8

describe the experiment in grasshoppers to show the stereotyped pathways of pioneers

Answer 8

Ti1 follows a specific pathway to the cell Cx1

when Cx1 is removed, the Ti1 stalls and doesnt know where to go