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Flashcards in Lecture 20 Deck (28):
1

How do different mechanism affect the pre-synaptic side?

Change the # quanta released per stimulus

2

How does facilitation affect vesicle release?

Increases the LIKELIHOOD that a vesicle's contents will be released
NO change to the size of each vesicle/amt of NT inside

3

Will one large stimulation cause facilitation?

NO - frequency dependent
More rapidly the nerve is stimulated - greater effect on EPSP

4

What is the mechanism that explains facilitation?

More stimuli = more depolarization = more Ca in pre-synaptic terminal
1. Lingering "on" machinery activated by Ca (priming)
2. Extra Ca adds to the depol of the next stimulus

5

What is depression?

Repeated pre-synaptic stimulation causes ever smaller EPSPs
↓# quanta released - again not about size

6

What mechanism explains depression?

Depleted pre-synaptic vesicles

7

Can you predict if depression of facilitation will be dominant at a synapse?

No
Both are present at varying degrees
Which one wins depends on the role of that synapse

8

Where on a neuron is a synapse a weak contributors to generating neuron depolarization?

Synapses on dendrites
Often far away from soma - signal becomes weaker the further it has to travel

9

Where on a neuron is a synapse a strong contributor to generating neuron depolarization?

Soma
Axon initial segment

10

What part of the neuron is the "detector" = determines whether a depolarization will occur? Why?

Axon initial segment
↑[Na channels] = low threshold
If depolarized, will send it down the length of the axon = myelinated

11

What is facilitation?

Pre-synaptic
Rapid stimulation causes increasingly large sized EPSPs

12

What are passive electronic characteristics of the neuron that contribute to EPSP decay as it travels?

Capacitance
Resistance
Current will escape through open ion channels as it travels

13

What is temporal summation?

Post-synaptic
2 potentials at same synapse in rapid succession
Additive

14

What is spatial summation?

Post-synaptic
2 potentials at 2 different synapses at the same time
Additive

15

How do neurons attempt to compensate for its own passive properties that lead to electronic decay of EPSPs with travel?

Active modulation
Add more Na channels to dendrites so that the signal can travel further

16

What is inhibition by shunting?

Inhibitory synapses near cell body
Will allow depolarizing (+) ions to leak out and it allows = ions to leak in
Loose current this way --> less excitatory input reaches the soma
"Prevents a depolarization"

17

Is the AMPA receptor excitatory or inhibitory? What is its NT?

Glutamate
Excitatory

18

What is long term potentiation? Are its effects transient or long lasting?

Elevated EPSP baseline (pre-stimulation)
Rapid stimulation --> gets progressive larger EPSPs --> then a SUSTAINED elevated baseline

19

What would block LTP?

NMDA-receptor antagonists
Is a Ca2+ channel - block this = no change in baseline

20

What 3 factors make us think LTP is linked to memory?

1. Persistant
2. Associative - requires events at both pre-synapse (glutamate release) and post-synaptic depol (via AMPA-R)
3. Specific - doesn't travel to affect neighboring synapses

21

What is LTP induction? Describe the process.

Detection of signal by NMDA receptor
1. MORE glutamate released than usual
2. Binds AMPA receptors --> STRONG post-synaptic depolarization
3. Remove Mg2+ NMDA receptor block
4. NMDA receptors open --> Ca2+ entry

22

How Ca2+ in the post-synapse cause LTP?

Activates protein kinases

23

With an elevated baseline from Ca2+ in the terminal, the synapse is now stronger meaning it can produced stronger depolarizations. How? (Hint: expression)

Insert new AMPA receptors into post-synaptic membrane
↑glutamate sensitivity of future stimuli

24

Where are new AMPA receptors often added for LTPs?

Dendritic spines!
Makes sense - where most synapses occur

25

Where do these new AMPA receptors come from?

Were part of reserve normally used to replace worn out AMPA receptors

26

What are 2 other changes that must happen to accommodate the ↑# AMPA receptors?

↑post-synaptic density
↑size of dendrite spines
(Both of these indicate a stronger synapse in general)

27

How are the LTP changes from induction/expression maintained?

Change in protein translation and transcription

28

What is long term depression? What is the mechanism: induction, expression, maintenance?

Low post-synaptic Ca
Mechanism = activates PHOSPHATASES
Weaken synapse
↓# AMPA-R
Spine and density shrinkage
Maintenance via translation/transcription