____ changes shape at decision points
how do neurons start (before polarization)?
round, with no obvious processes
___ defines the polarity of the neuron
where are growth cones located?
the tip of the axon
what are lamellapodium?
what do they contain?
fan shaped sheet at the tip of the axon
contain actin filaments and microtubles
what are filopodia? what do they contain?
fine processes extending out from lamellapodium
have actin filaments
___ growth cone form and disappear rapidly
___ dictates direction of growth - in lamellipodia / filopodia
Filamentous actin (F-actin)
____ gets incorporated into F-actin at leading edge
Gobular actin (G-actin)
F-actin Binding Proteins cause ___ and ___
retrograde flow & growth cone turning (by causing depolymerixation)
attractive cue increases ___ and decreases ___
↑ polymerization/assembly, ↓ retrograde flow (goes toward the attractive cue)
functional difference ebtween MT and F-actin
MT are responsible mostly for axon elongation
f-actin dictates direction
___ make the cytoskeleton core
Microtubules (they are strong and stable)
Acetylated microtubles only in ____
Tyrosinated microtubules ↑ in ____
where is f actin found?
in lamellipodium and filpodia
Contact repellants include
Semaphorins and Ephrins
Contact attractants include
1. peipheral ECM
___ are attractants inthe periphery, but are not well understood in the CNS?
what are examples of each?
attractants - laminins, collagens, fibronectin
not well understood? repellants? -- proteolgycens, glycoproteins, hyaloruonan
homolphilic binding of Cam
triggers cytoplasmic kinases of growth cone
what is Ca independent signaling? dependent
indepdent - CAM
Depdendent - caDherins
homophilic binding of cadherins triggers
intracellular signals --> actin binding &
axon guidance signsla re either ___ or ___
1. nondiffusable and short range
2. or diffusable and long range
the contact attraction and repulsion signals are ___
nondiffusable and short range
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 ____
repellant interactions promote ____
actin depolymerization and growth cone collapse
lamins, collagens, and fibronectins bind to ___
___ has been associated with bundling (fasiculation) of groups of axons as they grow