Week 1 - Synaptic Transmission Flashcards
criteria for chemical neurotransmitters
- present in presynaptic terminal
- released in response to stimulation; release must be Ca++ dependent
- specific receptors for neurotransmitter must be present on postsynaptic cell
- mechanism to inactivate neurotransmitter must be present (reuptake, enzymatic breakdown)
how are synaptic networks dispersed?
- spatially focused, subserving behaviors requiring precise timing
- widely dispersed and diffuse, subserving arousal, mood, and motivation
electrical synapses
- how fast are they?
- how do they flow?
- how are the pores and what does this mean?
extremely fast (little to no delay) with (mostly bidirectional) speed and synchrony
- allow direct passive flow of electronic current between cells via gap junctions
- pores are much larger than in voltage-gated or ligand-gated, thus permitting unselective diffusion of ions and substances like ATP and metabolites between cells
CNS synapses
electrical synapses are present in CNS, but much less common than chemical synapses
-brainstem neurons that regulate breathing are synchronized by electrical synapses
what do chemical synapses provide?
- directionality
- amplification
- potential for excitation/inhibition
- potential for plasticity/remodeling
- integration in space/time
what is necessary and sufficient for nt release?
rise in intracellular Ca++
- steep Ca++ gradient across presynaptic membrane, along with electrical gradient since positively charged
- travels through voltage-gated Ca++ channels, triggering vesicle fusion and nt release
what happens if you block voltage-gated Ca++ channels?
eliminates the postsynaptic response b/c no transmitter released
what does lowering external Ca++ concentration do?
decreases size of PSP by decreasing the number of vesicles that fuse to the membrane and release their NT
how fast is Ca clearance compared to entry?
entry of Ca++ is rapid, but clearance is slower, so Ca++ can build-up in the terminal
what is synaptic facilitation?
rapid increase in synaptic strength that occurs when 2+ AP invade presynaptic terminal w/in a few milliseconds of each other
- second EPSP is larger than the first, resulting from prolonged elevation of presynaptic Ca++ following synaptic activity
- when APs arrive in close succession, Ca++ builds up and allows more NT release in response to subsequent AP
- facilitation is not observed if 2 APs arrive far apart in time
is synaptic facilitation the same as temporal summation?
no; temporal summation is related to the number of APs and the time constant of the postsynaptic membrane
what do small molecule nt vesicles look like?
clear core, small (50 nm) vesicles made in nerve terminals (nt made in presynaptic terminal)
what do neuropeptide nt vesicles look like?
dense core, large (200 nm) vesicles synthesized in cell body and transported to nerve terminal via fast axonal, ATP-dependent transport
-vesicular release often requires high-frequency presynaptic activation
what does high-frequency stimulation lead to?
more generalized increase in Ca, causing release of both types of transmitter
relationship between active zones and postsynaptic densities
AZs - where subset of vesicles with small molecule transmitters are docked
PSDs - electron dense area with many receptors, aligned with presynaptic AZs
