Axonal Growth Lec03 Flashcards by brittany gouse

____ changes shape at decision points

growth cone

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how do neurons start (before polarization)?

round, with no obvious processes

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___ defines the polarity of the neuron

the axon

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where are growth cones located?

the tip of the axon

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what are lamellapodium?

what do they contain?

fan shaped sheet at the tip of the axon

contain actin filaments and microtubles

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what are filopodia? what do they contain?

fine processes extending out from lamellapodium

have actin filaments

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___ growth cone form and disappear rapidly

filopodia

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___ dictates direction of growth - in lamellipodia / filopodia

Filamentous actin (F-actin)

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____ gets incorporated into F-actin at leading edge

Gobular actin (G-actin)

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F-actin Binding Proteins cause ___ and ___

retrograde flow & growth cone turning (by causing depolymerixation)

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attractive cue increases ___ and decreases ___

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

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functional difference ebtween MT and F-actin

MT are responsible mostly for axon elongation

f-actin dictates direction

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___ make the cytoskeleton core

Microtubules (they are strong and stable)

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Acetylated microtubles only in ____

axons

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Tyrosinated microtubules ↑ in ____

lamellipodia

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where is f actin found?

in lamellipodium and filpodia

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Contact repellants include

Semaphorins and Ephrins

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Contact attractants include

peipheral ECM
CAM
Cadherins

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

what are examples of each?

ECM molecules

attractants - laminins, collagens, fibronectin

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

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homolphilic binding of Cam

triggers cytoplasmic kinases of growth cone

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what is Ca independent signaling? dependent

indepdent - CAM

Depdendent - caDherins

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homophilic binding of cadherins triggers

intracellular signals –> actin binding &
organization

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axon guidance signsla re either ___ or ___

nondiffusable and short range
or diffusable and long range

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the contact attraction and repulsion signals are ___

nondiffusable and short range

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the chemoattractants and chemorepulsive signals are

diffusable and long range

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

signaling cascades that result in the reognization of growth cone cytoskeletons --\> controlling **_the direction and rate at which the growth cone moves_**

attractive interactions (contact attractants and chemoattractants) promote \_\_\_\_

actin polymerization

repellant interactions promote \_\_\_\_

actin depolymerization and growth cone collapse

lamins, collagens, and fibronectins bind to \_\_\_

integrin receptors

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

L1 CAM

where can cadherins be found

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

where are semapghorins found?

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

where do sempahorins bind to?

cell surface --\> plexin family receptors secreted --\> bind neurophilins

what is the difference between the two classes of ephrins?

ephrin A has gpi linked ot surface ephrin b is a single pass transmembrane protein each has its own receptors on growth cone

why do temporal retina axons go to the anterior tectum?

ephrins A2 and A5 are lower in anterior -\> posterior A2 and A5 repulses the temporal axons since they have high A3

nasal retina go to the posterior tectum because

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

chemorepulsion molecules include

slits netrins if they have UNC 5 receptors

chemoattractant molecules include

netrin if they have DCC receptors

what is secreted at the embyro midline

chemorepulsants, so netrins and slits

what are slits receptors

robo

what receptors make netrin attractants

DCC

what receptors make netrin repiulsants

UNC 5

before crossing the midline ___ attracted to netrin at midline

DCC

after crossing the midline --\>

cell upregualtes robo receptors, repulsion from the midline

what silences DCC signaling?

the robo that is upregulated after crossing

what does KO of netrin eliminate?

the crossing of commisural axons

why do netrin and silts have to work together?

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

synaptogensis in CNS Presynaptic process (from growth cone) recognizes target cell via \_\_\_\_

cadherin

start of synaptgensis at the NMJ?

**1. mtoor axon approaches and amkes contact with a myotube**

in synaptogensis at NMJ after mtoor axons approaches the myotube.... what happens?

nerve terminal and mytotubual diffeerentiate nerve terminal becomes motor terminal muscle forms post synpatic apparatus

what is the differenation of muscle induced by?

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

what does MuSK do?

causes clustering and increased expression of acetylcholine receptors

in NMJ synaptogensis, both the motor nerve and muscle make

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

axons arising from **_t1_** in the superior cervical ganglia form synapses on cellbodies of neurons that

project to targets in the eye

axons arising from **_t4_** in the superior cervical ganglia form synapses on cellbodies of neurons that

project to targets in the ear

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

they have a higher affinity than the wrong combinations

CNS synaptogensis what recognizes the appropriate site on target cell

nascent presynaptic process via cadherin/protocadherin family

CNS synaptogensis ## Footnote immediately after nascent process recognizes the target cell --\>

synaptic vesicles and active zone components accumulate

CNS synaptogensis ## Footnote what is recruited in the developing synapse tob ring in moilecules?

neurexin and neuroglin

where is neurorxin found? what is its function

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

where is neuroglin found? what is its function?

postsynp. membrane function -- recruits NT receptors and other postsynatpic proteins

After synaptogenesis, target cells secrete

limited amounts of neurotrophic factors.

which neurons survive after synaptogensis?

those that receive enough trophic factors

Neurotrophins control the

of target cells contacted and # of synapses formed

what happens if there is NGF in check sensory ganglion? if there is none?

yes NGF -- explosion of axon extensions no NGF -- neuron death

\_\_\_ respond to all growth factors

dorsal root ganglion

nodose ganglia respond best to

NT3

Sympathetic ganglia respond best to \_\_\_? and not at all to \_\_\_?

best to -- NGF not at all to BDNF

neutrophin receptors include --

Trk and p75 receptors

Trk receptors ahve a high affinity for

processed/cleaved neutrphins

p75 have a high affinity for

unprocessed enutrophin

intially, skeletal muscle and some aprsymp neurons are innveratvated by

multiple neurons | (this is eventually pruned)

with synapse elimation at the nmj, comeptition is dependent on

electricial activity in both pre and post synaptic cells

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

persistence of polyneuronal innervation

axonal branching patterns are refined via

competition and synapse elimination

BDNF, NT3, NT 4/5 are all

growth factors

what is evidence for the trophic function of NGF?

no NGF --\> neuronal death excessive NGF --\> survival of excess neurons NGF are present (and produced) in target cells) NGF

neutrophic interactions depend on

neurotrophins secreted by target cells the neurorophin receptors present intracellualr signaling cascade present

neutrophic interactions determine--

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

Axonal Growth Lec03 Flashcards

(79 cards)