Ii-21: Neurodevelopment 2 - Construction Of Neural Circuits

Front 1

What is the function of a growth cone?

Back 1

To navigate the connection from a neuron to its target

Front 2

How does a growth cone form?

Back 2

Spot on neuron becomes active --> begins to migrate away from body

Front 3

How does an axon form?

Back 3

As growth cone migrates, it leaves a string of cytoplasm that remains connected to the cell body

Front 4

What are filopodia?

What are their features/functions?

Back 4

Spike like protrusions on the edge of the growth cone

1. Contain actin
2. Have dynamic movements
3. sense chemical environment
4. respond to stable environments by stabilizing
5. Respond to unfavorable environments by retracting

Front 5

What exists in the center of the growth cone/axon?

Back 5

microtubules

Front 6

What makes the signaling molecules that guide growth cones?

Where are the receptors?

Back 6

Target cells and cells along route of growth make proteins to guide

Filopodia have specific receptors

Front 7

What happens when a Filopodium binds an attractant?

Back 7

Filopodium is stabilized, growth cone pulled along

Front 8

What happens when a Filopodium binds a repellant?

Back 8

Filopodium retracts, growth cone heads in another direction

Front 9

What determines the attractive/repulsive nature of the signals to growth cones?

Back 9

The receptors

Front 10

How do long-range signaling molecules work?

Back 10

Signaling molecules secreted into fluid around cell --> diffuse away from source, forming concentration gradient

Can act on growth cones from a dsitance

Front 11

How do short-range signal molecules work?

Back 11

Remain anchored to the membrane of the cell that makes them, must come in contact with the growth cone

Front 12

What are the 4 kinds of growth cone guidance signals?

Back 12

Long range attractive
Long range repulsive
Short range attractive
Short range repulsive

Front 13

What are commissural neurons?

Back 13

Interneurons in dorsal horn --> send axons carrying pain/temperature info to the ventral midline --> decussate and ascend rostrally

Front 14

What type of signaling takes place to allow commissural axons to grow? Where do they go?

Back 14

Long range attraction by netrin

Grow toward floor plate

Front 15

What does netrin do?

Back 15

Expresed by floor plate cells --> diffuses dorsally from within neural tube --> conc. gradient --> can attract axons from dorsal neural tube

Front 16

Why do commissural axons ascend rostrally after crossing the floor plate?

Back 16

When the growth cone contacts the floor plate cells, its receptors change --> no longer respond to netrin, but rather to other signals

Front 17

How can netrin act as a long-range rupulsive signal?

Back 17

Different receptors on growth cones respond to netrin differently

Front 18

What type of signals guide retinotectal axons?

Where do they go?

Back 18

Short-range repulsin by ephrins

Travel to dorsal midbrain (sup. colliculus or tectum)

Front 19

To what structure in the tectum do the anterior retinal neurons project?

posterior retinal neurons?

Back 19

Posterior tectum

Anterior tectum

Front 20

What is the chemoaffinity hypothesis?

Back 20

Different parts of the retina are chemically different and neurons in the tectum have corresponding differences that allow the retinal growth cones to find the right place

Front 21

How does ephrin work on axons from the temporal retina?

Back 21

Ephrins expressed in gradients in the tectum, anchored to cell membrane --> short-range signal to REPULSE growth cones from temporal retina

Front 22

How do fascicles form?

Back 22

Short range attraction

One axon bears CAMS, which is attractive to the growth cone of a second, developing axon

Front 23

What are pioneer neurons?

Back 23

Neuron that is laid down early in development that can navigate a complex pathway for later born axons to follow

Front 24

How does regeneration of axons occur?

Why does regeneration not occur in the CNS?

Back 24

Selective fasciculation - short-range attractive signals are produced by glia

In CNS, white matter contains lots of short-range repulsive signals

Front 25

What do axon guidance molecules do at synapse formation?

Back 25

Act as cadherins, help form synapse

Front 26

What is postsynaptic density?

Back 26

Specialized intercellular junction that localizes NT receptors

Front 27

What are neurexin and neuroligin?

Back 27

Molecules that help set up a synapse

Neurexin = presynaptic
neuroligin = postsynaptic

Front 28

What has been associated with mutations in neuroligins?

Back 28

Autism

Front 29

During development, how many neurons are made?

Back 29

Neurons are made in excess, then half die

Front 30

How does a neuron survive once it establishes a synapse?

Back 30

Neuron becomes dependent on the target for survival and differentiation

Front 31

What accounts for changes in the shape of the ventral horn of the spinal cord as you go rostrally to caudally?

Back 31

Neurons that fail to make a connection to a target die

Motor neurons in cervical and lumbar regions synapse w/ muscles, survive

Motor neurons in thoracic regions do not synapse, die

Front 32

What do neutrotrophic factors control? (2)

Back 32

Number and shape of synapses on target

Control shape and growth of axonal and dendritic branches

Front 33

What are target-derived neurotrophic factors?

examples

Back 33

Secreted by target cells

NGF, BDNF, NT3 and NT4

Front 34

How do neurotrophic receptors work?

Some examples?

Back 34

Receptors in growth cones or synapses bind specific neurotrophins --> endocytosis --> neurotrphins transported back along axon to cell body --> promote cell survival

TrkA, TrkB, TrkC

Front 35

What 3 processes are affected by neurotrophic signaling?

Back 35

1. cell survival/death
2. neurite outgrowth/differentiation
3. activity-dependent synaptic stabilization or elimination

Front 36

What are embryonic stem cells?

Back 36

Totipotent cells isolated from the ICM of a blastocyst- can give rise to any cell type and self-renew

Front 37

How can ES cells be inducd towards a neural lineage?

What if you add FGF?
Shh?

Back 37

culture density, addition of retinoic acid

FGF - results in spinal cord (caudal) neurons

Shh - ventral types (motor, interneurons) rather than dorsal neurons

Front 38

From where can neural stem cells be derived (somatic)? (3)

How do they reproduce?

Back 38

Can come from embryonic stem cells, embryonic neural tissue, or adult neural tissue

Self-renew

Front 39

What are 2 regions of the adult brain that have neurogenesis occuring and what do they produce?

Back 39

1. Subventricular zone of lateral ventricles --> olfactory bulb neurons

2. Subgranular layer in the dentate gyrus of hippocampus --> granule neurons