axonal growth synaptogenesis and tropism

Question 1

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

Answer 1

neuronal polarization

Question 2

what is the first step in neuronal polarization?

Answer 2

extension of neurites .

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

Question 3

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

Answer 3

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

Question 4

what are the morphological characteristics of growth cones?

Answer 4

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)

Question 5

where do growth cones get signals from?

Answer 5

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

Question 6

how do growth cones react to environment?

Answer 6

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

Question 7

__________microtubules have been around longer than ________microtubules

Answer 7

acetylated microtubules have been around longer than tyrosinated microtubules.

Question 8

what is fasciculation?

Answer 8

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

Question 9

_____are primarily responsible for axon elongation

Answer 9

microtubules

Question 10

f Actin does what?

Answer 10

dictates direction of axon turning

Question 11

f actin binding to f actin binding proteins does what?

Answer 11

regulates retrograde flow

Question 12

where are tyrosinated microtubules located ?

Answer 12

they are enriched in lamellipodia

Question 13

where are acetylated microtubules?

Answer 13

in axons ( only)

Question 14

where is f-actin?

Answer 14

lamellipodia and filopodia

Question 15

what is repulsive especially for regeneration after spinal cord injury?

Answer 15

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

Question 16

_______in the matrix are both diffusible and non-diffusible

Answer 16

proteoglycans

Question 17

what are L1 cell adhesion molecules important for?

Answer 17

they are attractants important for fasciculation

Question 18

cadherin is a ______?

Answer 18

homophilic attractant ( they are non-diffusible)

Question 19

semaphorins are _______? and lead to_________?

Answer 19

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

Question 20

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

Answer 20

Ephrins ( they are non-diffusible)

optic tectum

Question 21

what projects to the anterior optic tectum?

Answer 21

temporal axons ( lateral part of the axon)

Question 22

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

Answer 22

temporal retina

Question 23

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

Answer 23

nasal retina

Question 24

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

Answer 24

nasal axons, nasal axons

Question 25

_______ is attractive to netrin.

Answer 25

DCC

Question 26

________ is repellant to netrin.

Answer 26

UNC5

Question 27

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

Answer 27

commissural neurons

Question 28

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

Answer 28

crossing the spinal cord

Question 29

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

Answer 29

Robo ( receptor)

Question 30

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

Answer 30

slit

Question 31

robo interacts with DCC to do what?

Answer 31

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

Question 32

how does the initial formation of the PNS synapse occur?

Answer 32

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

Question 33

How does the CNS synapse form?

Answer 33

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.

Question 34

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

Answer 34

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

Question 35

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

Answer 35

selectiive higher affinity

Question 36

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

Answer 36

the same long range guidance cues innervate different set of neurons

Question 37

describe the innervation of muscle cells at birth?

Answer 37

they are initially poly-innervated

Question 38

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

Answer 38

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

Question 39

_____ _______ direct axons to target cells?

Answer 39

guidance molecules

Question 40

where do axons form synapses?

Answer 40

on selected target cells

Question 41

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

Answer 41

they are refined via competition and synapse elimination

Question 42

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

Answer 42

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

Question 43

do all cells respond to all neurotrophins?

Answer 43

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

Question 44

what are some examples of neurotrophins?

Answer 44

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

Question 45

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

Answer 45

NT-3

Question 46

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

Answer 46

NGF don't respond to BDNF

Question 47

what are Trk receptors and what is their fnc?

Answer 47

tyrosine kinase receptors (which bind to a subset of neurotrophins

Question 48

what are the 3 Trk receptors?

Answer 48

TrkA TrkB and TrkC

Question 49

all three Trk receptors only have an affinity for ________

Answer 49

processed (cleaved) neurotrophins

Question 50

Which neurotrphins activate the p75 receptor?

Answer 50

all of them

Question 51

p75 has ___ affinity for unprocesed neurotrophins

Answer 51

high

Question 52

p75 has ___ affinity for procesed neurotrophins

Answer 52

low

Question 53

What Trk receptor does NGF mainly use?

Answer 53

TrkA

Question 54

What Trk receptor does NT-3 mainly use?

Answer 54

TrkC

Question 55

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

Answer 55

TrkB

Question 56

which neurotrophin is key in activity dependent plasticity?

Answer 56

BDNF

Question 57

what are the 4 axon guidance signal types?

Answer 57

2 nondiffusible: ( short range) 1. contact attraction 2. contact repulsion 2 diffusible ( long range): 1.chemoattraction 2. chemorepulsion

Question 58

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

Answer 58

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

Question 59

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

Answer 59

repulsive | they include hyaluronan, proteoglycan, and glycoproteins

Question 60

Cadherins are Calcium independent or dependent? choose one

Answer 60

Cadherins are calcium dependent ( cadbury chocolate depends on calcium)

Question 61

CAMs are Calcium independent or dependent? choose one

Answer 61

CAMs are calcium independent