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Flashcards in Axonal Growth Lec03 Deck (79)
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1
Q

____ changes shape at decision points

A

growth cone

2
Q

how do neurons start (before polarization)?

A

round, with no obvious processes

3
Q

___ defines the polarity of the neuron

A

the axon

4
Q

where are growth cones located?

A

the tip of the axon

5
Q

what are lamellapodium? 

what do they contain? 

A

fan shaped sheet at the tip of the axon

contain actin filaments and microtubles

6
Q

what are filopodia? what do they contain?

A

fine processes extending out from lamellapodium

have actin filaments

7
Q

___ growth cone form and disappear rapidly

A

filopodia

8
Q

___ dictates direction of growth - in lamellipodia / filopodia

A

Filamentous actin (F-actin) 

9
Q

____ gets incorporated into F-actin at leading edge

A

 Gobular actin (G-actin)

10
Q

F-actin Binding Proteins cause ___ and ___

A

retrograde flow & growth cone turning (by causing depolymerixation)

11
Q

 attractive cue increases ___ and decreases ___ 

A

↑ polymerization/assembly, ↓ retrograde flow (goes toward the attractive cue)

12
Q

functional difference ebtween MT and F-actin 

A

MT are responsible mostly for axon elongation

f-actin dictates direction

13
Q

 ___ make the cytoskeleton core

A

Microtubules (they are strong and stable)

14
Q

Acetylated microtubles only in ____

A

axons

15
Q

 Tyrosinated microtubules ↑ in ____

A

lamellipodia

16
Q

where is f actin found?

A

in lamellipodium and filpodia

17
Q

Contact repellants include

A

Semaphorins and Ephrins

18
Q

Contact attractants include

A

1. peipheral ECM

2. CAM

3. Cadherins

19
Q

___ are attractants inthe periphery, but are not well understood in the CNS?

what are examples of each?

A

ECM molecules

attractants - laminins, collagens, fibronectin

not well understood? repellants? -- proteolgycens, glycoproteins, hyaloruonan

20
Q

homolphilic binding of Cam 

A

triggers cytoplasmic kinases of growth cone

21
Q

what is Ca independent signaling? dependent

A

indepdent - CAM

 

Depdendent - caDherins

22
Q

homophilic binding of cadherins triggers

A

intracellular signals --> actin binding &
organization

23
Q

axon guidance signsla re either ___ or ___

A

1. nondiffusable and short range

2. or diffusable and long range

24
Q

the contact attraction and repulsion signals are ___

A

nondiffusable and short range

25
Q

the chemoattractants and chemorepulsive signals are 

A

diffusable and long range

26
Q

what does the binding of axon guidanc emolecules to receptors on growth cones activate?

A

signaling cascades that result in the reognization of growth cone cytoskeletons --> controlling the  direction and rate at which the growth cone moves

27
Q

attractive interactions (contact attractants and chemoattractants) promote ____

A

actin polymerization

28
Q

repellant interactions promote ____

A

actin depolymerization and growth cone collapse

29
Q

lamins, collagens, and fibronectins bind to ___

A

integrin receptors

30
Q

___ has been associated with bundling (fasiculation) of groups of axons as they grow

A

L1 CAM

31
Q

where can cadherins be found

A

on the suface of growth cones, growing axons, surrounding cells or targets

32
Q

where are semapghorins found?

A

can be secreted or anchored to the cell surface

(secreted are probably attached to the cell surface or the ECM --> not really diffusable)

33
Q

where do sempahorins bind to?

A

cell surface --> plexin family receptors

secreted --> bind neurophilins

34
Q

what is the difference between the two classes of ephrins?

A

ephrin A has gpi linked ot surface

ephrin b is a single pass transmembrane protein

 

each has its own receptors on growth cone 

35
Q

why do temporal retina axons go to the anterior tectum?

A

ephrins A2 and A5 are lower in anterior

 

-> posterior A2 and A5 repulses the temporal axons since they have high A3

36
Q

nasal retina go to the posterior tectum because

A

axons from the nasal retina are blind to ephrin and lack the eph receptor

 

so they don't be repulsed by ephrins A2 and A5 found highly in the posterior tectum

37
Q

chemorepulsion molecules include

A

slits

netrins if they have UNC 5 receptors

38
Q

chemoattractant molecules include

A

netrin if they have DCC receptors

39
Q

what is secreted at the embyro midline

A

chemorepulsants, so netrins and slits

40
Q

what are slits receptors

A

robo

41
Q

what receptors make netrin attractants

A

DCC

42
Q

what receptors make netrin repiulsants

A

UNC 5

43
Q

before crossing the midline ___ attracted to netrin at midline

A

DCC

44
Q

after crossing the midline --> 

A

cell upregualtes robo receptors, repulsion from the midline

45
Q

what silences DCC signaling?

A

the robo that is upregulated after crossing

46
Q

what does KO of netrin eliminate?

A

the crossing of commisural axons

47
Q

why do netrin and silts have to work together?

A

because the cells have to cross at a very specific site in the spinal cord

also cant recross

48
Q

synaptogensis in CNS

 Presynaptic process (from growth cone) recognizes target cell via ____

A

cadherin

49
Q

start of synaptgensis at the NMJ?

A

1. mtoor axon approaches and amkes contact with a myotube

50
Q

in synaptogensis at NMJ

after mtoor axons approaches the myotube.... what happens?

A

nerve terminal and mytotubual diffeerentiate

nerve terminal becomes motor terminal

muscle forms post synpatic apparatus

51
Q

what is the differenation of muscle induced by?

A

agrin --> activating MuSK --> causing clustering and increased expression of acetylcholine receptors

52
Q

what does MuSK do?

A

causes clustering and increased expression of acetylcholine receptors

53
Q

in NMJ synaptogensis, both the motor nerve and muscle make

A

ecm components to form a basa lamina (to stabilize the synaptic structure)

54
Q

axons arising from t1 in the superior cervical ganglia form synapses on cellbodies of neurons that 

A

project to targets in the eye

55
Q

axons arising from t4 in the superior cervical ganglia form synapses on cellbodies of neurons that 

A

project to targets in the ear

56
Q

how do the correct pre and post synaptic neurons in superior cervical ganglion find eachother

A

they have a higher affinity than the wrong combinations

57
Q

CNS synaptogensis

 

what recognizes the appropriate site on target cell

 

A

nascent presynaptic process via cadherin/protocadherin family

58
Q

CNS synaptogensis

immediately after nascent process recognizes the target cell -->

A

synaptic vesicles and active zone components accumulate

59
Q

CNS synaptogensis

what is recruited in the developing synapse tob ring in moilecules?

A

neurexin and neuroglin

60
Q

where is neurorxin found?

what is its function

A

presynatpic

function -- localizes cytoskeltal elements, vesciles, active zone proteins, and Ca channels TO PRESYNAPTIC MEMBRANE 

61
Q

where is neuroglin found? 

what is its function?

A

postsynp. membrane

function -- recruits NT receptors and other postsynatpic proteins

62
Q

After synaptogenesis, target cells secrete

A

 limited amounts of neurotrophic factors.

63
Q

which neurons survive after synaptogensis?

A

those that receive enough trophic factors

64
Q

Neurotrophins control the 

A

# of target cells contacted and # of synapses formed

65
Q

what happens if there is NGF in check sensory ganglion?

 

if there is none?

A

yes NGF -- explosion of axon extensions

no NGF -- neuron death

66
Q

___ respond to all growth factors

A

dorsal root ganglion 

67
Q

nodose ganglia respond best to

A

NT3

68
Q

Sympathetic ganglia respond best to ___? and not at all to ___?

A

best to -- NGF

not at all to BDNF

69
Q

neutrophin receptors include -- 

A

Trk and p75 receptors

70
Q

Trk receptors ahve a high affinity for

A

processed/cleaved neutrphins

71
Q

p75 have a high affinity for

A

unprocessed enutrophin

72
Q

intially, skeletal muscle and some aprsymp neurons are innveratvated by

A

multiple neurons

(this is eventually pruned)

73
Q

with synapse elimation at the nmj, comeptition is dependent on 

A

electricial activity in both pre and post synaptic cells 

74
Q

blocking electrical acitivity in either pre or post synaptic cells results in

A

persistence of polyneuronal innervation

75
Q

axonal branching patterns are refined via

A

competition and synapse elimination

76
Q

BDNF, NT3, NT 4/5 are all

A

growth factors

77
Q

what is evidence for the trophic function of NGF?

A

no NGF --> neuronal death 

excessive NGF --> survival of excess neurons

NGF are present (and produced) in target cells)

NGF

78
Q

neutrophic interactions depend on

A

neurotrophins secreted by target cells

the neurorophin receptors present

intracellualr signaling cascade present

79
Q

neutrophic interactions determine--

A

number of neurons, shape of neurons, patterns of neuronal connections