L13 GOK

Question 1

whats the difference in axon collatorals in the invertebrate and vertebrate brain ?

Answer 1

invertebrate - few

vertebrate - many

Question 2

modes of axon branching ?

Answer 2

arborisation - branching of axon terminals
bifurcation - branching of axon terminals
collateral formation - middle of axon branches

Question 3

arborisation occurs where usually ?

Answer 3

within the target

Question 4

whats a good example of delayed interstitial branching ?

Answer 4

layer 5 pyramidal neurons

Question 5

what part of the developing neuron is involved in target selection ?

Answer 5

GC and axon shaft just behind GC

Question 6

explain activity dependent collateral elimination

Answer 6

axons innnervate too many targets during development
collaterals pruned based on activity
- no activit eliminated/ die due to lack of stimulation

Question 7

projections retained by Layer V neurons

are dependent on where they?

Answer 7

develop not where they are born

transplant motor neurons into the visual cortex - these neurons will project to the sup colliculus

Question 8

in relation to topographic mapping which part of the brain has been widely studied ?

Answer 8

retina -> superior colliculus (mammals) or optic tectum

Question 9

what is the sup colliculus involved in ?

Answer 9

eye movements particularly saccades

Question 10

Visual field divided into ?

Answer 10

nasal and temporal , dorsal and ventral

Question 11

temporal axons terminate where?

nasal axons terminate where?

Answer 11

T -rostral SC

N - caudal SC

Question 12

who carried out experiments on frog RGC ?

Answer 12

Sperry

Question 13

what did Sperrys eye experiements show ?

Answer 13

molecular mapping rather than functional molding of random connections

Question 14

GAP 4 is a marker for what ?

Answer 14

growing axons

Question 15

what is a membrane stripe assay ?

Answer 15

cut a strip out of retina explant with nasal and temporal sections and culture them on membranes isolated from caudal and rostal sc

Question 16

what did the stripe assay show ?

Answer 16

temporal axons only grow on rostral membrane

nasal axons grow on both rostral and caudal membranes

Question 17

why do temporal axons only grow on rostral membranes ?

why does boiling the axons causes ?

Answer 17

because they have receptors that respond to inhibitory signals from caudal membrane

denatures receptors and temporal axons grow everywhere

Question 18

why do nasal axons grow everywhere ?

Answer 18

because they will have to pass through the rostral sc before they get to caudal

Question 19

what type of repulsion are ephrins involved in ?

Answer 19

contactrepulsion

Question 20

level of ephrin expression in rostral and caudal sc?

Answer 20

r - low

c - high

Question 21

level of ephrin receptor expression in temporal and nasal axons

Answer 21

t - high

n - low

Question 22

why do nasal only have a small number of receptors for ephrin ?

Answer 22

want to stop at caudal SC

low no. of receptors needs high ephrin signalling at caudal SC to collapse GC and stop migrating axon

Question 23

dorsal and ventral parts of the retina eph B expression ?

Answer 23

D -low L - high
V - high M - low

receptors EphB d and V
ligand ephrin B L and M