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Flashcards in Synaptic Transmission Deck (26):
1

synapses

cell-to-cell communication occurs here
cells come in contact
-electrical synapse
-chemical synapse

2

electrical synapse

gap junction; connexons(6 per pore)
fastest; nearly simultaneous
bidirectional
synchronized signal; large neural network
interneurons, hormone secreting neurons in hypothalamus

3

chemical synapse

AP arrives, local increase in cytoplasmic Ca2+ -> synaptic vesicles fusion
neurotransmitter released into synaptic cleft
binds to specific receptor on postsynaptic cell

4

transmission sequence

transmitter stored in synaptic vesicle
AP enter
depolarization/Ca2+ channels open
influx of Ca2+
synaptic vesicles fuse
release transmitters
transmitter diffuse across synaptic cleft
transmitter binds to receptors
ion channels open or close - PSC can be either excitatory(EPSP) or inhibitory(IPSP)
vesicular membrane recycled

5

EPSP and IPSP

excitatory post synaptic potential
inhibitory post synaptic potential

6

Loewi's experiment

chemical neurotransmission
ACh in mAChR - contraction slowed down; inhibitory

7

neurotransmitter criteria

1. present within the presynaptic neuron; enzymes, precursors
* some needed for protein synthesis: glutamate, glycine, aspartate

2. released by depolaration and require Ca2+ influx

3. receptors must be present on post synaptic cell

8

exogenous? agonist? Antagonist?

exogenous transmitters can mimic
agonists and antagonists can alter transmission

9

(synaptic transmission at ) neuromuscular junction

neuron stimulated -> muscle membrane potential occurs : EPP (end-plate potential)
large enough to evoke AP

10

MEPP

* fusion of one vesicle (quanta) releasing its NT
spontaneous changes in muscle membrane potential
miniature(<1mV) EPP(40-50mV); look similar when compared to subthreshold EPP; integer multiples of MEPP
can be blocked by drugs that block postsynaptic receptors

11

Freeze fracture analysis

to study quantal release of NT
# of fusion vs. #of quanta

12

Role of Ca2+

AP not prevented when Na+ channel blocked
voltage gated Ca2+ channel
* cadmium (ca2+ channel blocker) blocks both pre- and post- synaptic current/depolarization
sufficient and necessary

13

Ca2+ sufficient?

microinjection of Ca2+ in presynaptic nerve terminals evoke release even when AP was not present

14

Ca2+ necessary?

Ca2+ buffer blocked depolarization in postsynaptic neuron

15

two types of transmitters

small molecule
peptides

16

small molecule neurotransmitters

synthesized in presynaptic terminals
enzymes made in soma trnsported by slowaxonal transport
precursor transported into the nerve terminal
synthesized and packaged into vesicles
* final steps of synthesis sometimes occurs in vesicle
small clear core vesicles

17

neuropeptide

precursors synthesized in cell body
transported by fast axonal transport; kinesins
in terminal, enzymes modify precursors to produce the neuropeptides
when released, diffused away and degraded( proteolyticm enzyme)

18

release of small molecule NT or neuropeptides

low frequency stimulation -> local increase of Ca2+ -> small molecule NT
high frequency stimulation -> more diffuse in Ca2+ concentration -> neuropeptide and small molecule NT released

19

synaptic vesicles resued

experiment: HRP-horseradish peroxidase
budding (endosome)->docking->priming (exocytosis) ->fusion->budding (endocytosis)

20

coating

clathrin triskelion
vesicle recovered (endocytosis)
Adaptor proteins AP-2 & AP-180 facilitate
Dynamin; final pinching
HSC-70, auxilin, synaptojanin: uncoat

21

vesicle docking

complex: synaptobrevin&syntaxin&SNAP-25
Ca2+ controled: synaptotagmin; evoke fusion

22

SNARE complex

synaptobrevin, syntaxin, snap-25
pull membranes together
Ca2+ binds to synaptotagmin
synaptotagmin catalyzes membrane fusion

23

LEMS

attacks presynaptic Ca2+ channels

24

Congenital myasthenic syndrome

impared vesicle recycling

25

Botulinum and tetanus toxins

clostridial toxin
affect SNARE proteins involved in vesicle fusion

26

Clostridial toxin

protease
tetanus toxin, botulinum toxin
cleave presynaptic SNARE proteins