lecture 9 Flashcards
(27 cards)
electrical synapse
transfer of signals without delay
synchronize networks of neurons
no change in sign
chemical synapse
release of vesicles through synapses - some delay
gap junction
direct current flow
6 connexions
large enough for 1000 dalton molecule to get through
lamprey
composite electrical-chemical synapses
mix electrical synapses with chemical
chemical response is delay because NT release is slow
fast chemical synapse
a synapse with a delay between pre/post of about < 1msec
always release small molecules
temporal fidelity for fast transmission requires tight temporal coupling between pre synap depolarization and NT release
what happens when using a Ca channel blocker
if you block presynaptic Ca current you block release (giant squid synapse)
non linear release dependant on Ca
Ca channels are co-localized and have a low affinity so it will only open if concentration is really high and channel is close by
means transmitter release will turn on and off in specific times
calculate release
release = k (Ca)^ 4
if you double calcium you get 16x release
funnel web spider toxin (AgaIVA)
cone snail toxin (omega conotoxin GVIA)
designed to block calcium channels
block relay messages
other propositions for transmitter release
Ca gated channels- no driving force (Ach wants to go in of cell not out)
pump - too slow
only practical way is to bundle in vesicles - solves problem of high [] without osmotic effect
MEPP and EPP
MEPP- spontaneous depolarizations
EPP- subthreshold - stimulate and see depolarization within 1msec
- synchronized to AP because tied in time to Ca influx
what happens to MEPP if Ca inside terminal is increased
the frequeuncy is increased but not the size of MEPP
always around 0.4mV
composed of multiple independant events with a unit size of 0.4mV
3 factors of size of post synaptic response to release event
size of one unit# of available quantap of release of unit*
= k * n * p
n of synaptic vesicles
must be docked (close to membrane) and primed (ready to release)
vesicles in back of neuron are tied up in meshwork of actin
clatharin
assembles with itself to form a vesicle from membrane
dynamin required to pinch off membrane (ATP)
kiss and run
vesicle doesnt fully fuse with post synaptic membrane
dynamin could help vesicles from fully fusing and pinch back off - would result in empty vesicles with the proper proteins to function
components of SNARE complex
synaptobrevin- vesicule membrane (VAMP)
SNAP-25 - embedded in synaptic membrane
syntaxin- presynaptic membrane
synaptotagmin - 1 end in vesicle, associated with Ca
Munc18
docking and priming also involves
as well as complexin and ATP
fusion step of vesicle binding
requries Ca and ATP
one hypothesis that Ca binding changes lipid solubility of synaptotagmin providing a force to pull membrane together to fuse
what happens if you dont have ATP
not required for release but you will run out of vesicles and not be able to dissasemble them
botox
cleaves snare complex and prevents transmitter release
LEMS- attacks presynaptic Ca channel and lowers probability of release
frog nmj
example of fast synapse
active zones lined up with channels
tight vesicle colocalization
RIM/RIM-BP binding to Ca achieves tight colocolization
creates an anchor
active zones
docked vesicles are arranged into active zones
colocalized with calcium channels and other proteins
