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neuroscience > axonal growth synaptogenesis and tropism > Flashcards

axonal growth synaptogenesis and tropism Flashcards

1
Q

________is the first step in neuronal identity and the formation of connections.

A

neuronal polarization

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2
Q

what is the first step in neuronal polarization?

A

extension of neurites .

1 neurite becomes the axon but it is some what random as to which one becomes the axon.

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3
Q

what happens if you cut off the neurite that is to become the axon?

A

another neurtie will become the axon therefore there is some flexibility as to which neurite is the axon

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4
Q

what are the morphological characteristics of growth cones?

A

lamella podium ( ruffling membrane at tip of axon containing actin filaments and microtubules) and filopodia ( finger like projections extending from the lamellapodium; contain actin; form and disappear rapidly)

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5
Q

where do growth cones get signals from?

A

they react to the environment directly rather than reacting to a signal from the nucleus.

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6
Q

how do growth cones react to environment?

A

they sense calcium in the environment and also have lots of receptors.

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7
Q

__________microtubules have been around longer than ________microtubules

A

acetylated microtubules have been around longer than tyrosinated microtubules.

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8
Q

what is fasciculation?

A

when axons travel along one another ( guide each other) and follow each other to chemo attractant and split in the case of chemorepulsion.

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9
Q

_____are primarily responsible for axon elongation

A

microtubules

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10
Q

f Actin does what?

A

dictates direction of axon turning

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11
Q

f actin binding to f actin binding proteins does what?

A

regulates retrograde flow

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12
Q

where are tyrosinated microtubules located ?

A

they are enriched in lamellipodia

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13
Q

where are acetylated microtubules?

A

in axons ( only)

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14
Q

where is f-actin?

A

lamellipodia and filopodia

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15
Q

what is repulsive especially for regeneration after spinal cord injury?

A

chondritin sulfate ( but it plays a diff role in early development)

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16
Q

_______in the matrix are both diffusible and non-diffusible

A

proteoglycans

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17
Q

what are L1 cell adhesion molecules important for?

A

they are attractants important for fasciculation

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18
Q

cadherin is a ______?

A

homophilic attractant ( they are non-diffusible)

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19
Q

semaphorins are _______? and lead to_________?

A

repellants which lead to depolarization of actin. ( they are non-diffusible)

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20
Q

_______are bi directional signalers, which are usually repellant and affects actin and ligand. they also play an important role in ________.

A

Ephrins ( they are non-diffusible)

optic tectum

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21
Q

what projects to the anterior optic tectum?

A

temporal axons ( lateral part of the axon)

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22
Q

axons from the _____ ________ are repulsed by ephrin in posterior tectum because they express high levels of an Eph receptor.

A

temporal retina

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23
Q

axons from the ________ _______ are blind to ephrin because they lack a eph receptor.

A

nasal retina

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24
Q

_____ ______ projects to posterior optic tectum , something else is directing the ________ _______ to the posterior.

A

nasal axons, nasal axons

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25
Q

_______ is attractive to netrin.

A

DCC

26
Q

________ is repellant to netrin.

A

UNC5

27
Q

what crosses the spinal cord and can’t cross back?

A

commissural neurons

28
Q

DCC is initially expressed in the neural cone which leads to_______?

A

crossing the spinal cord

29
Q

up regulation of _________ occurs as soon as commissural neurons cross the spinal cord.

A

Robo ( receptor)

30
Q

after comissural neurons cross over and robo is unregulated the receptor for ____ is activated and the neurons are repulsed from crossing over.

A

slit

31
Q

robo interacts with DCC to do what?

A

further silence DCC’s attraction to prevent recrossing over of commissural neurons

32
Q

how does the initial formation of the PNS synapse occur?

A

peripheral nerve releases agrin which binds to MusK ( receptor- a tyrosine phosphatase) which activates Ach receptors through the cytoplasmic linker protein rapsyn

33
Q

How does the CNS synapse form?

A

We are not yet sure but there are lots of protocadherins in the CNS and it is thought that the homophilic interactions of protocadherins is probably the first step.

34
Q

what type of cell is critical in determining the number of cells that get innervated and why ?

A

target cells because they release neurotrophic factors and cells that don’t have enough neurotrophic factor apoptose.

35
Q

Synapse formation must be _________: the correct pre- and post synaptic neurons have __________ __________ each other

A

selectiive

higher affinity

36
Q

T1 and T4 axons use the same ______________ ________ to reach ganglion but each innervate _________ set of neurons

A

the same long range guidance cues

innervate different set of neurons

37
Q

describe the innervation of muscle cells at birth?

A

they are initially poly-innervated

38
Q

what happens to muscles cells after birth ( in maturity)?

A

each muscle fiber gets it’s own nerve fiber ( usually occurs but not always)

39
Q

_____ _______ direct axons to target cells?

A

guidance molecules

40
Q

where do axons form synapses?

A

on selected target cells

41
Q

how are axonal branching patters refined ( i/e how does a poly-innervated muscle at birth become ( single-ly ) innervated in maturity?

A

they are refined via competition and synapse elimination

42
Q

in addition to contributing to the survival of a subset of neurons what else do neurotrophins

A

they elaborate axonal and dendritic branches to support connections ( the number of synapses formed)

43
Q

do all cells respond to all neurotrophins?

A

no, different cells respond to different neurotrophins, except dorsal root ganglia respond to all growth factors

44
Q

what are some examples of neurotrophins?

A

Nerve growth factor ( NGF)
BDNF
NT-3
NT 4/5

45
Q

what growth factor ( neurotrophin) do nodose ganglia neurons respond to most robustly?

A

NT-3

46
Q

what growth factor ( neurotrophin) do sympathetic ganglia neurons respond to most robustly and which don’t they respond to at all?

A

NGF

don’t respond to BDNF

47
Q

what are Trk receptors and what is their fnc?

A

tyrosine kinase receptors (which bind to a subset of neurotrophins

48
Q

what are the 3 Trk receptors?

A

TrkA TrkB and TrkC

49
Q

all three Trk receptors only have an affinity for ________

A

processed (cleaved) neurotrophins

50
Q

Which neurotrphins activate the p75 receptor?

A

all of them

51
Q

p75 has ___ affinity for unprocesed neurotrophins

A

high

52
Q

p75 has ___ affinity for procesed neurotrophins

A

low

53
Q

What Trk receptor does NGF mainly use?

A

TrkA

54
Q

What Trk receptor does NT-3 mainly use?

A

TrkC

55
Q

What Trk receptor do BDNF and NT-4/5 mainly use?

A

TrkB

56
Q

which neurotrophin is key in activity dependent plasticity?

A

BDNF

57
Q

what are the 4 axon guidance signal types?

A

2 nondiffusible: ( short range) 1. contact attraction 2. contact repulsion

2 diffusible ( long range): 1.chemoattraction 2. chemorepulsion

58
Q

in the PNS name 3 attractive substrates for growth cones and what do they bind to?

A

lamins, collagens, and fibronectin

they bind to integrins which triggers a series of signaling cascades leading to axon growth and elongation

59
Q

the CNS matrix molecules are largely ________? they include________,_______, and _________

A

repulsive

they include hyaluronan, proteoglycan, and glycoproteins

60
Q

Cadherins are Calcium independent or dependent? choose one

A

Cadherins are calcium dependent ( cadbury chocolate depends on calcium)

61
Q

CAMs are Calcium independent or dependent? choose one

A

CAMs are calcium independent

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