MT - Neuronal Function (Part 4): Synaptic Transmission Flashcards
What differentiates the structure of an electrical synapse from that of a chemical synapse?
Electrical: gap junctions join presynaptic and postsynaptic cells
Chemical: synaptic cleft between presynaptic and postsynaptic cells
What is the name given to the functional protein complexes in gap junctions? What kind of synapses are these present in?
In electrical synapses, the functional protein complexes are called connexins.
How do electrical synapses allow a signal to pass from the presynaptic to the postsynaptic cell?
By allowing the passage of ions through aqueous pores called connexins. This changes the membrane potential.
What differentiates the directionality of chemical synapses from electrical synapses?
Chemical: unidirectional
Electrical: bidirectional
How was the movement of solutes through an electrical synapse proved?
Injection of dye into the presynaptic cell diffueses and fills the postsynaptic cell.
How would you calculate the coupling coefficient of two cells joined at an electrical synapse?
From cell 1->cell 2, K= R2 / (R2+Rc)
-Where R2 is resistance of cell 2 and Rc is resistance of coupling.
What ion is required for chemical synaptic transmission and mediates release of neurotransmitter vesicles into the synaptic cleft?
Calcium!
How many calcium ions are needed to mediate the release of a single neurotransmitter vesicle?
4 (bind to synaptotagmin).
Who discovered the acetylcholine neurotransmitter? How?
Otto Loewi noticed that if you stimulate the vagus nerve of a frog it decreases heart rate. Moved the solution that the heart was in to another heart and observed the same thing!
What is the term used to refer to the smallest unit of neurotransmitter release?
“Quantal” release. Actually found before they knew that this was the amount of neurotransmitter contained in a vesicle.
In what part of the synapse are docked vesicles arranged prior to neurotransmitter release?
The “active zone”.
Are all chemical synapse active zones the same? Elaborate.
No, they can have various arrangements of Ca-channel colocalization around the vesicles.
What equation gives the mean size of postsynaptic response from a chemical synapse?
Response = # of available sites * prob. of release @ any site * response from 1 quanta. (PSR = n p q)
What protein in the membrane of synaptic vesicles binds calcium?
Synaptotagmin.
What 4 steps outline vesicle fusion at the presynaptic membrane?
- SNARE complexes form
- Synaptotagmin binds complex
- Ca2+ binds synaptotagmin
- Membrane fusion
What are the 2 membrane fusion proteins in the presynaptic vesicles?
- Synaptobrevin
2. Synaptotagmin
What are the 2 membrane fusion proteins in the presynaptic membrane?
- Syntaxin
2. SNAP-25
What happens to vesicles following fusion with the presynaptic membrane and neurotransmitter release?
They are retrieved by endocytosis.
What protein forms the coat around vesicles as they are being recovered from the presynaptic membrane post-fusion? How are these budded off?
Clathrin. Dynamin disconnects the vesicles from the membrane.
Are GPCRs ionotropic or metabotropic?
Metabotropic (slow, non-ionic).
What differentiates temporal summation from spatial summation?
Temporal: small, slightly staggered potentials cause net change of memb. pot.
Spatial: small potentials from various sites combine to cause net change of memb. pot.
Are spatial summation and temporal summation distinct in-vivo?
No. They’re both really co-occurring all the time in the neurons.
Describe the release of ACh at cholinergic synapses, starting from Acetyl CoA synthesis.
- Acetyl CoA produced by mitochondria
- Acetyl CoA -> ACh
- ACh packaged in vesicles
- ACh released into synapse
- ACh binds to receptor
- ACh -> choline + acetate
- Acetate diffuses, choline is recycled
How many receptor subunits make up a muscle nicotinic ACh receptor? What are they?
Pentameric (5 subunits). 2 * α, β, γ/ε, δ.
How many receptor subunits make up a neuronal nicotinic ACH receptor? What are they?
Pentameric (5 subunits). 1-5 * α, 1-3 * β.
Where on the nicotinic ACh receptors do ligand(s) bind?
2 ligands bind to the α subunits to activate.
What ion channels are fluxed through nicotinic ACh receptors?
Cations: Na+, K+, Ca2+.
What is the reversal potential (equilibrium potential) for nicotinic ACh receptors?
~0mV.
Are nicotinic ACh receptors excitatory or inhibitory?
Excitatory (depolarizes the membrane).
What mechanism ensures that ACh signalling remains brief?
Acetylcholinesterase hydrolyzes ACh to choline and acetate.
What are the 3 kinds of ionotropic glutamate receptors?
- AMPA receptors
- NMDA receptors
- Kainate receptors
How many subunits are required to form an ionotropic glutamate receptor?
4.
What do ionotropic glutamate receptors Kainate and AMPA require for opening? What ions do they flux?
They require only glutamate binding to open. Flux Na+ and K+.
What does ionotropic glutamate NMDA receptor require for opening? What ions does it flux?
Requires membrane depolarization and glutamate/glycine binding to open. Flux Na+, K+, and Ca2+.
What ion can NMDA receptors flux that AMPA and Kainate receptors can not?
Calcium.
What is the reversal potential (equilibrium potential) for ionotropic glutamate receptors?
~0mV.
Are ionotropic glutamate receptors excitatory or inhibitory?
Excitatory (depolarizes the membrane).
How is glutamate removed from the synaptic cleft?
By glutamate transporters EATT on the presynaptic cell or on supporting glial cells.
How many subunits are required to form a GABA receptor?
Pentameric (5 subunits).
What is the reversal potential (equilibrium potential) for GABAa receptors?
~-99mV (the Nernst potential of Cl-).
What ion do GABA receptors flux?
Cl-.
Are GABAa receptors excitatory or inhibitory?
Inhibitory (hyperpolarize the membrane).
