lecture 10: communication between nerve cells Flashcards
small synaptic vesicles
- SSVs are attached to the presynaptic plasma membrane and clustered nearby
- drawn to accumulating at the synaptic region
classification of SSV pools
- readily releasable pool: SSV docked at the active zone
- reserve pool: distal to active zone, associated with cytoskeleton, important as they allow for a sustained release of neurotransmitter
- recycling pool : diffusing
summary of presynaptic events at chemical synapses
- AP in bouton generated by opening of Na+ channels
- AP travels via axon to reach the presynaptic nerve terminal: Na+ channels
- depolarization opens Ca2+
- Ca2+ elevation occurs in microdomain
- ca2+ influx triggers “exocytotic machine” = mechanisms that allows for release of pre docked synaptic vesicles to release neurotransmitter (and neuromodulators) from synaptic vesicles (signals excytosis = neurotransmitter release)
–> FAST
synaptic vesicle cycle process
- NT uptake
- translocation
- docking
- priming prefusion
- fusion exocytosis
- endocytosis
- translocation
- endosome fusion
- budding
synaptic vesicle cycle summary from slides
- formed in the golgi apparatus and transported along microtubules to axons
- enter the “vesicle cycle”
- filled in nerve terminal
- release neurotransmitter
- recycled via endocytosis to endosomes or reserve pool
- refilled via transporters
–> exocytosis and endocytosis
VGLUTs (vesicular glutamate transporter)
- found only in glutamatergic neurons and are used to uniquely identify these neurons using immunocytochemistry
Exocytosis
= release of neurotransmitter
what does exocytosis require
RAB proteins –> translocation and docking
SNARE proteins –> exocytosis
Synaptotagmin –> allows fusion pore to open
- Ca2+ dependent
SNARE proteins function
linkage, pulls and tethers the synaptic vesicle to the axon axonal membrane
synaptobrevin (v-SNARE)
important part of docking and tethering of the synaptic vesicle to the plasma membrane
–> vesicle associated membrane protein, VAMP
syntaxin (t-SNARE) and SNAP25 (t-SNARE)
on the plasma membrane side, twist around to dock the synaptic vesicle at the plasma membrane
synaptotagmin
- synaptic vesicle protein
- calcium sensor
- docking
- triggers vesicle fusion/release
- couple Ca2+ influx thorugh voltage gated Ca2+ channels to vesicle fusion and thus neurotransmitter release
- important bc its the calcium sensor
process of exocytosis
- vesicle inside a cell fuses with the cell membrane and releases its contents outside the cell
–> vesicle containing neurotransmitter fuses with presynaptic membrane
–> fusion is triggered by an influx of ca2+ ions which occurs when an AP reaches the axon terminal
exocytosis –> full collapse fusion
- vesicle collapse into the plasma membrane
- release all content
exocytosis –> ‘kiss and run”
- fusion pore opens and closes
- all content is not released
endocytosis
= the process by which vesicle membrane is retrieved back into the cytoplasm
= recycling
–> ensures that axon terminals continue to function properly even after sustained neurotransmitter release
what does endocytosis require
clathrin = assists in the formation of a coated pit on the inner surface of the plasma membrane of the cell, which buds into the cell to form a coated vesicle
dynamin:
- GTPase
- binds to a forming bud on the membrane
- forms a helical collar around the neck of the bud
–> GTP hydrolysis is coupled to vesicle scission
–> dynamin spirals undergo a length-wise extension which pinches or pops the vesicle from the parent membrane
