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Hebbian And Synaptic Plasticity Flashcards

1
Q

Importance of Donald Hebb

A

Two neurons become stronger synapsed with more use, stronger association

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2
Q

What is Hebb’s rule

A

Neurons that fire together, wire together

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3
Q

What is hebbian plasticity

A

Basic PRINCIPLE that learning and memory can occur due to changes in the strength of connections between neurons
- Hebb inferred the principle without knowing the mechanisms

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4
Q

What are the mechanisms for hebbian plasticity

A

Long-term potentiation (LTP)
Long-term depression (LTD)

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5
Q

Define homeostasis

A

Body’s ability to maintain a set point

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6
Q

Homeostatic plasticity function

A

Move neurons back to set point (original stage) after modification

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7
Q

What does continual excitation cause

A

Excitotoxicity
-mess up ATP production, mitochondria issues

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8
Q

Explain long-term potentiation

A

Synaptic activity increases future post-synaptic potentials
Or
Excitation at synapse determines greater excitability in the future

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9
Q

What/when was the first evidence of LTP

A

1973
Trains of high frequency APs led to increased EPSP
- prove EPSP increase in future after excitation at synapse

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10
Q

What is a high frequency value

A

50 Hz

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11
Q

How are synaptic experiments recorded

A

Electrode- pre synaptic neuron
Recorder- post synaptic neuron

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12
Q

How is LTP triggered

A

High sustained Ca in post synaptic neuron triggers LTP
- intracellular Ca signalling

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13
Q

What does LTP cause, what is this dependent on

A

Structural changes at the postsynaptic terminal
Dependent on glutaminergic receptors (AMPA/NMDA)

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14
Q

What kind of channels are NMDA and AMPA

A

NMDA- Ca channel (also permeable to Na, K)
AMPA- Na channel (also permeable to K)

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15
Q

What kind of receptors are NMDA and AMPA

A

Glutamate receptors

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16
Q

Explain LTP pathway for NMDA and AMPA (when there is a depolarizing signal)

A

Local depolarization removes Mg from NMDA (at RMP NMDAR is blocked by Mg)
Ca influx through NMDA (in postsynaptic membrane) activates intracellular CaMKII pathway (CaMKII is Ca dependent kinase)
Insertion of AMPAR in post synaptic membrane (inside neuron brought to surface) via vesicular fusion caused by kinase phosphorylation (now have more post synaptic channels, can generate larger EPSP)

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17
Q

Provide details for AMPAR

A
  • tetrameric (4 subunits) can choose from GluA1-4
  • central Arg provides specificity
  • inward current at negative mV (Na)
  • outward current at positive mV (K)
  • without GluA2 inwardly rectifying
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18
Q

Provide main function of NMDAR

A

Trigger LTP: strong activation of NMDAR lead to large increase in postsynaptic Ca
Trigger LTD: modest activation of NMDAR leads to modest increase in postsynaptic Ca

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19
Q

AMPA and NMDA are non-selective ion channels so where is their reversal potential

A

Near zero (I vs V graph)

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20
Q

Draw the NMDAR and AMPAR current vs voltage graph

A

AMPA should have 2- with and without GluA2
Pg. 7 of Hebbian

21
Q

How does LTD happen

A

Moderate Ca levels trigger PP2B and PP1
PP2B- calcineurin
PP1- protein phosphatase 1
These phosphatase s’ s remove P from AMPAR and recall receptors into postsynaptic cell via endocytosis
Receptors can be reused later

22
Q

Explain molecular events that lead to increase in AMPAR during LTP

A

Transport of endosomes important for AMPAR insertion
- involves Rab, syntaxin, synaptotagmin, complexin
Laterally diffusing AMPAR must be trapped at nanodomains
- involves CaMKII and P-PDZ stargazin
Phosphorylation results in binding of stargazin to PSD-95
(stargazin and PSD-95 are structural proteins that physically anchor receptor to membrane)

23
Q

Role of cadherens

A

Transmembrane proteins that tether the pre and post membranes together- physically strengthen synapse

24
Q

EPSP outcome after increasing AMPA

A

Overall greater, same NMDA current and greater AMPA current
There is a comparative graph on pg 10

25
Result of hippocampus damage
Inability to make new memories
26
Importance of hippocampus and location
Connections critical for formation of long-term memories - medial temporal lobe structure with well-characterized regions (Ca1, CA3, dentate gyrus)
27
Patient H.M.
Bilateral loss of hippocampi produces anterograde amnesia or inability to form new memories
28
What 4 structures form a neural circuit
CA1 CA3 DG (dentate gyrus) EC (entorhinal cortex)
29
Function of EC
Entorhinal cortex is a bridge between the hippocampus and the cortex
30
Describe pathway of 4 structure neural circuit
EC gets input from cortex and gives it to hippocampus Dentate gyrus receives input from EC and projects to CA3 CA3 receives input from DG and from EC CA1 major output goes to layer V of EC
31
What can stimulation to EC cause
Repeated stimulation of EC cells that project to DG leads to increased EPSPs in DG (consistent w Hebbian principles)
32
Requirements for hippocampus LTP
- input specificity: only activated synapses will potentiate (get LTPed) - cooperativity: enough presynaptic axons must fire coincidentally (at same time) to activate the post synaptic neuron (to get LTP)
33
Values for frequency levels
50 Hz - high 10 Hz - medium 1 Hz - slow
34
Experiment for hippocampal plasticity
Measure post synaptic EPSP. Induce LTP in lab Test and control pathway. Stimulus to Schaffer collaterals (using different synapses on CA1 neuron for two conditions) CA3 neurons project to CA1 neurons Electrode in CA3 Schaffer collaterals provide depolarization Recording electrode in CA1 Test pathway- 10 Hz frequency paired with post synaptic depolarization (paired pulse protocol) Control pathway- CA1 neuron never depolarized, constant 10 Hz amplitude, no EPSP generation
35
When does LTD occur
Long-term depression happens because of - short term decreases caused by inactivation of Cav channels - depletion of NT containing vesicles
36
What is LTD
Temporary decrease in post synaptic excitability
37
Factor that determines if a synapse will strengthen
Frequency of stimulation it receives
38
How does LTD occur
Activation of phosphatases that act on synaptic proteins to regulate synapse strength - proteins: cadherins, catenins, PSD95 - phosphatases also remove P from AMPA cause endocytosis
39
Function cadherins vs catenins and PSD-95
Cadherins - outside of cell, tether neurons at synapse Catenins and PSD-95 (post synaptic density) - intracellular, link AMPA to cytockeleton
40
Localizationism and connectionism: what? Key takeaway is they both are important for history of neurology
Localizationism (where in brain)- particular functions for particular regions or groups of neurons Connectionism (neural circuit/connections)- particular functions for connected neurons
41
Does Hebbian plasticity prove Localizationism or connectionism
Connectionism - provides a connectionist account of learning, memory, development
42
Where are memories stored? What does this prove?
Short term- hippocampus Long term- cerebral cortex, thalamus (36 days after learning) Explains why loss of hippocampus prevents new memories but old memories remain in tact Shows that memories are plastic
43
Proof the brain is plastic
Trevor Greene- severed motor cortex but was able to rewalk - following traumatic injury, functional brain responses can be remapped through new groups of neurons being recruited
44
How does plasticity change during development
Child- connections are stronger between neurons that are anatomically close but functionally unrelated Teens/adults- connections are stronger between neurons that are functionally related but distant
45
Why are connections between neurons important
Learning and memory encoding
46
What does neural plasticity allow for
Education Training Recovery
47
Amount of connections at birth, 7, 15
Birth- few 7- most 15- less than7, synaptic pruning. LTD weakens unnecessary synapses
48
Snail experiments
Article and pg 20 Scientists made snails remember something that didn’t happen to them 1. Extract RNA from trained snails and put in untrained. Upon shock the untrained snails responded the same as the trained snails (siphon retract for long period) 2. Untrained snail brain cells in dish with trained RNA, shock neurons and saw them fire same was as trained neurons

BPK 306 (18 decks)

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