Lecture 18 Flashcards Preview

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Flashcards in Lecture 18 Deck (20):
1

Describe the physical structure of an electrical synapse.

Usually gap junctions
Connexons form channels between cells
PASSIVE movement of ions and small molecules (ATP) can pass through the water pore

2

Do you see transmission delay in electrical synapses?

NO - immediate transmission

3

Do you see amplitude changes between pre/post electrical synapse?

Yes - amount of decline depends on resistance

4

Are electrical synapses easily blocked by reagents (toxins) that affect chemical transmission?

No! Don't have anything to attach to!

5

What are 2 variations of axo-dendritic synapses?

1. Directly onto the dendrite shaft
2. Onto dendrite spine

6

Describe the calyx of Held neuronal synapse.

Usually auditory
Pre-synapse = "hand", many synaptic connections

7

Of the axo-dentritic/axonic/somatic connections, which are generally inhibitory vs excitatory?

Axo-D = excitatory
Axo-S = tends inhibitory, more middle
Axo-A = inhibitory

8

Describe the action of events in a firing chemical synapse.

Pre-synapse AP
Open pre-s Ca2+ channels
Ca2+ entry causes vesicle fusion
Release NT
Post-synaptic response - change in membrane permeability (ex: open receptor gated Na channels to cause depol)

9

What is an EPSP?

Excitatory post-synaptic potential
The ability of a pre-synaptic AP tending to evoke a depolarization of the post-synaptic cell via NT response

10

What is an EPSC?

Excitatory post-synaptic current
If the EPSP reaches threshold, will yield an EPSC
Larger EPSP (depol) --> larger EPSC (current)

11

Can chemical synapses be blocked by toxins?

YES!

12

Is Ca2+ required for NT release?

YES
No Ca2+ - no NT release

13

Is a change in voltage required for NT release?

NO
Only need Ca2+ rise!

14

Do you see transmission delays with chemical synapses? What is the reasoning behind your answer?

Yes!
Primary cause = presynaptic
- Opening Ca channels
- Time takes to activate release mechanism
NT release and diffusion time contributes

15

What is the active site/synapse/release site relationship?

1 active site constitutes a synapse
1 active site can have many release sites

16

Is 1 Ca2+ ion enough to trigger a release event?

No
Need several
↑ strength of pre-synaptic depol --> more Ca2+ released --> ↑↑↑ amount of NT released

17

How does the amount of Ca change the NT release?

Changes the # of vesicles likely to release contents - NO change in the amount of NT per vesicle
- ↑Ca2+ pre-s = more vesicles fused for release

18

What is the quantal hypothesis?

NTs are released in small packets = quanta
1 vesicle contains 1 quanta of NT

19

How many quanta can be released per release site?

1
Remember, an active zone can have multiple release sites - how 1 synapse can release multiple vesicles worth NTs

20

What is a MEPP? What is the relationship between MEPP and EPSP?

MEPP = mini endplate potentials = random, small depolarizations that result in NT release (think mini EPSP)
EPSPs are the result of many simultaneous MEPPs - the size of an EPSP is a multiple of the smallest MEPP NT bundle