Flashcards in Lecture 18 Deck (20):
Describe the physical structure of an electrical synapse.
Usually gap junctions
Connexons form channels between cells
PASSIVE movement of ions and small molecules (ATP) can pass through the water pore
Do you see transmission delay in electrical synapses?
NO - immediate transmission
Do you see amplitude changes between pre/post electrical synapse?
Yes - amount of decline depends on resistance
Are electrical synapses easily blocked by reagents (toxins) that affect chemical transmission?
No! Don't have anything to attach to!
What are 2 variations of axo-dendritic synapses?
1. Directly onto the dendrite shaft
2. Onto dendrite spine
Describe the calyx of Held neuronal synapse.
Pre-synapse = "hand", many synaptic connections
Of the axo-dentritic/axonic/somatic connections, which are generally inhibitory vs excitatory?
Axo-D = excitatory
Axo-S = tends inhibitory, more middle
Axo-A = inhibitory
Describe the action of events in a firing chemical synapse.
Open pre-s Ca2+ channels
Ca2+ entry causes vesicle fusion
Post-synaptic response - change in membrane permeability (ex: open receptor gated Na channels to cause depol)
What is an EPSP?
Excitatory post-synaptic potential
The ability of a pre-synaptic AP tending to evoke a depolarization of the post-synaptic cell via NT response
What is an EPSC?
Excitatory post-synaptic current
If the EPSP reaches threshold, will yield an EPSC
Larger EPSP (depol) --> larger EPSC (current)
Can chemical synapses be blocked by toxins?
Is Ca2+ required for NT release?
No Ca2+ - no NT release
Is a change in voltage required for NT release?
Only need Ca2+ rise!
Do you see transmission delays with chemical synapses? What is the reasoning behind your answer?
Primary cause = presynaptic
- Opening Ca channels
- Time takes to activate release mechanism
NT release and diffusion time contributes
What is the active site/synapse/release site relationship?
1 active site constitutes a synapse
1 active site can have many release sites
Is 1 Ca2+ ion enough to trigger a release event?
↑ strength of pre-synaptic depol --> more Ca2+ released --> ↑↑↑ amount of NT released
How does the amount of Ca change the NT release?
Changes the # of vesicles likely to release contents - NO change in the amount of NT per vesicle
- ↑Ca2+ pre-s = more vesicles fused for release
What is the quantal hypothesis?
NTs are released in small packets = quanta
1 vesicle contains 1 quanta of NT
How many quanta can be released per release site?
Remember, an active zone can have multiple release sites - how 1 synapse can release multiple vesicles worth NTs