Synaptic Transmission

Question 1

synapses

Answer 1

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

Question 2

electrical synapse

Answer 2

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

Question 3

chemical synapse

Answer 3

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

Question 4

transmission sequence

Answer 4

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

Question 5

EPSP and IPSP

Answer 5

excitatory post synaptic potential

inhibitory post synaptic potential

Question 6

Loewi’s experiment

Answer 6

chemical neurotransmission

ACh in mAChR - contraction slowed down; inhibitory

Question 7

neurotransmitter criteria

Answer 7

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

Question 8

exogenous? agonist? Antagonist?

Answer 8

exogenous transmitters can mimic

agonists and antagonists can alter transmission

Question 9

(synaptic transmission at ) neuromuscular junction

Answer 9

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

Question 10

MEPP

Answer 10

• 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

Question 11

Freeze fracture analysis

Answer 11

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

Question 12

Role of Ca2+

Answer 12

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

Question 13

Ca2+ sufficient?

Answer 13

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

Question 14

Ca2+ necessary?

Answer 14

Ca2+ buffer blocked depolarization in postsynaptic neuron

Question 15

two types of transmitters

Answer 15

small molecule

peptides

Question 16

small molecule neurotransmitters

Answer 16

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

Question 17

neuropeptide

Answer 17

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)

Question 18

release of small molecule NT or neuropeptides

Answer 18

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

Question 19

synaptic vesicles resued

Answer 19

experiment: HRP-horseradish peroxidase

budding (endosome)->docking->priming (exocytosis) ->fusion->budding (endocytosis)

Question 20

coating

Answer 20

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

Question 21

vesicle docking

Answer 21

complex: synaptobrevin&syntaxin&SNAP-25

Ca2+ controled: synaptotagmin; evoke fusion

Question 22

SNARE complex

Answer 22

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

Question 23

LEMS

Answer 23

attacks presynaptic Ca2+ channels

Question 24

Congenital myasthenic syndrome

Answer 24

impared vesicle recycling

Question 25

Botulinum and tetanus toxins

Answer 25

clostridial toxin

affect SNARE proteins involved in vesicle fusion

Question 26

Clostridial toxin

Answer 26

protease
tetanus toxin, botulinum toxin
cleave presynaptic SNARE proteins