Synaptic Transmission Flashcards
Is synaptic transmission unilateral?
Yes
What are the two types of synaptic transmission and which one is faster?
Electric transmission is faster than chemical
What do chemical synapses generate that add to create an action potential?
PSP (postsynapticpotentials)
What are the channel cells composed of in electric gap junctions?
6 connexins
What is the mechanism of electric synapse transmission?
It is the flow of ions directly from cytoplasm to cytoplasm
What does the PSP of an electric synapse look like after one presynaptic action potential?
It slightly depolarises
What kind of junction established principles of synaptic transmission?
The Neuromuscular Junction
What are 4 types of CNS synapse based off of connectivity?
Axodendritic - to dendrite
Axoaxonic - to another axon
Axosomatic - to cell body
Dendrodendritic - dendrite to dendrite
What are characteristics of the two Gray’s types of chemical synapse?
Type 1 - Asymmetrical membrane differentiations, excitatory
Type 2 - Symmetrical membrane differentiations, inhibitory
When a synapse lands on a dendritic spine, does the post synaptic neuron fire an action potential?
Not necessarily!
What depolarization is required for an action potential?
-40mV
How many mV is an EPSP roughly?
0.5mV
How did Otto Loewi contribute to the understanding of NTs in 1932?
He injected saline from an electrically generated slow heart frog heart that slowed down the heart of another without electrical stimulation
What are the 7 steps of chemical synapse transmission?
- Neurotransmitter synthesis
- Loading of NTs into vesicles
- Fusion of vesicle to membrane at presynaptic nerve terminal
- Release of NT into synaptic cleft
- Binding of NT to postsynaptic receptors
- Postsynaptic response
- Removal of NTs from synaptic cleft
Why is it important that receptors have low affinities for their NTs?
Because they should only be activated by high concentrations of NT
What are the three types of NT? What are they (with popular examples)?
Amino Acids - Small Amino Acids (GABA, glutamate)
Amines - Small amino acids (dopamine, acetylcholine)
Peptides - short amino acid chains (dynorphin)
Where are NTs synthesized?
Amino acids + amines = enzymes at nerve terminals
Peptides = The ER/packaged in the Golgi apparatus
What ion stimulates exocytosis?
Intracellular Ca2+
What is the nature of Ca2+ gates?
They are voltage gated, but slower than Na+ gates
Describe the two types of vesicle content emptying into the synapse
- Kiss and run, energetically favorable that creates a small opening that connects the vesicle and presynaptic membrane
- Full collapse into the presynaptic membrane
What process recovers vesicle membranes?
Endocytosis
What does the stochastic nature of transmitter release entail?
Most of the time there are actually synaptic failures, and nothing happens after an action potential in terms of NT release, and sometimes NT release has different effects on the PSP
What is the quantal unit of NT transmission?
Vesicles
What is the quantal hypothesis of NT release?
Based off of the amplitude of the end-plate potentials, we can assign probabilities of single, double, etc. quantal events
In a NMJ, how many synaptic vesicles would be released for an EPSP of how much?
Roughly 200 vesicles woul dbe released for an EPSP of roughly 40mV
What direction does voltage go in an EPSP or IPSP?
EPSP - Voltage depolarizes +
IPSP - Voltage polarizes -
In a CNS synapse, what happens in an EPSP?
One vesicle is released for a change of only a few tenths of a milivolt
What is an ionotropic receptor?
It is a transmitter-gated ion channel
What is the full formula for the current of an EPSP?
I (epsp) = N(total number of channels) * p0 (probability they’re open) * y(conductance of one) * (vm - Eepsp)(driving force)
Why is the reversal potential for Vepsp and Iepsp zero?
Because both Na and K channels flux with voltage changes
What are the 4 mechanisms of NT recovery/degradation?
- Diffusion away from the synapse
- Reuptake into the presynaptic axon terminal
- Enzymatic destruction in the synaptic cleft or terminal cytosol
- Desensitization, ie. Enzyme deactivates a NT
What do receptor antagonists do? What is an example of this?
Inhibit neurotransmitter receptors (curare)
What do receptor agonists do? What is an example of this?
Mimic naturally occurring NTs e.g. Nicotine
What is the root cause of neurological and psychiatric disorders?
It is defective neurotransmission
What is synaptic integration?
It is the process where multiple synaptic potentials combine in one postsynaptic neuron
What are the three types of EPSP summation that allow for sophisticated computations?
Integration - EPSPs added together
Spatial - Coordinated EPSPs at different areas
Temporal - EPSPs generated at the same synapse in rapid succession
How do dendrites contribute to synaptic integration?
Depolarization falls off with increasing distance of the dendrite
What is the formula for the depolarization of the membrane based off of the length of the dendrite?
Vx = V0/e^(x/y(dendritic length constant))
Why are dendrites considered excitable?
They have voltage gated channels as well, and can act as amplifiers
How can dendrites carry signals in the opposite direction?
Their sodium channels
What is the difference between an IPSP and a shunting inhibition?
IPSP = Membrane potential less an -65mV
Shunting inhibition = Current flow inhibited from soma to axon hillock
