Synaptic Transmission Flashcards
Golgi staining of neurons is based on the precipitation of ____ ions and reveals detailed morphology of ____ ___.
Silver
Single cells
Reticular theory vs neuron doctrine: what does each state and which one is correct?
Reticular theory: neurons are a network that is one continuous connection (incorrect)
Neuron theory: neurons are separate cells with space between them; one cell must release and the other must detect (correct)
Synaptic cleft
Gap between pre- and post-synaptic neuron
Action potential causes release of _____ from the ___- synaptic terminal.
Neurotransmitters
Pre
Binding of neurotransmitter causes what to open on the post-synaptic neuron?
Ion channels
Ions flowing through channels causes change in the resting membrane potential of what on the post-synaptic cell?
Dendrites
Changes in membrane potential from dendrites is “integrated” where?
Axon hillock
The axon ___ ___ is enriched in voltage-gated K+ and Na+ channels.
Initial segment
If the membrane potential is above threshold, voltage-gated channels in the axon will do what?
Fire an action potential
The action potential travels what way down the axon?
Distally
Which is more common, a chemical or electrical synapse?
Chemical
In an electrical synapse, ____ flow from one cell to another through what?
Ions
Gap junction
A gap junction creates a ____ channel.
Continuous
Are the channels in electrical synapses ever closed?
No- they are always open
Is the distance between cells in an electrical synapse large or small?
Small
Is the pore size in an electrical synapse large or small? What 3 things can pass through the pores of an electrical synapse?
Large
Ions, ATP, neurotransmitters
What is the directionality of an electrical synapse?
Bidirectional
Is the speed of an electrical synapse fast or slow? How much time between pre- and post-synaptic neurons firing?
Fast
Less than 1 ms
Can many or few things modulate an electrical synapse?
Few
In a chemical synapse, a pre-synaptic neuron releases a _____ that binds to a post-synaptic neuron’s ____, causing an ____ ____.
Chemical
Receptors
Action potential
Is the distance between cells in a chemical synapse larger or smaller than that of an electrical synapse? Relatively speaking, is it large or small?
Larger
Small
Is the pore size of a chemical synapse larger or smaller than that of an electrical synapse? What can pass through it?
Smaller
Only ions
What is the directionality of a chemical synapse?
Unidirectional
Is the speed of a chemical synapse fast or slow? In comparison to an electrical synapse? How much time between pre- and post-synaptic neurons firing?
Fast
Slow
2-3 ms
Can many or few things modulate a chemical synapse?
Many
In a chemical synapse, are synaptic vesicles found on the pre- or post-synaptic side?
Pre-synaptic side
In a chemical synapse, is the pre- or post-synaptic side denser?
Post-synaptic side
A glioblastoma tumor cell forms what kind of synapse because it functions as a part of the synapse? What type of polarization feeds the tumor cell?
Tripartite synapse (interacts with synapse) Depolarization
In what type of synapse can signals such as ions travel directly from one cell to another without passing through the extracellular space?
Electrical synapse
Neurons signal to each other through what?
Neurotransmitters
In an experiment to determine how neurons signal to each other, 2 frog hearts were connected to each other how? When the vagus nerve of the first heart was stimulated, causing the force and frequency of heartbeat to go down, what happened to the next? What does that prove?
Containers- solution could flow from one heart to another
Force and frequency of heartbeat also went down
Neurons release something that enables signalling
The neuromuscular junction is made up of what synapsing on what?
Motor neuron
Muscle fiber
In a muscle fiber, what happens when depolarization brings membrane potential above threshold?
Muscle contracts
What is the end plate in the neuromuscular junction?
Synapse of the neuromuscular junction
What is the end plate potential?
Depolarization of muscle fiber before contraction
What is the neurotransmitter released at the neuromuscular junction?
Acetylcholine
In reference to the end plate of the neuromuscular junction, what is a “mini” and what is it caused by?
Small depolarization
Release of synaptic vesicles from pre-synaptic side
Studying minis at the neuromuscular junction requires blocking the ____ channels using TTX so that what doesn’t occur?
Na
Action potential
In regards to minis at the neuromuscular junction, what is spontaneous vs evoked release?
Evoked release is when the minis are synchronized due to stimulation of the motor axon, whereas spontaneous release involves waiting and watching (not synchronized)
The mini end plate potential (mEPP) changes in amplitude by a factor of x (x, 2x, 3x, 4x). What is x measuring?
How much pre-synaptic cell causes depolarization in post-synaptic cell
In regards to mini end plate potential (mEPP), what is a quantum?
Amount of post-synaptic depolarization caused by the release of neurotransmitter from 1 synaptic vesicle
Graphically, what is the relationship between quanta and vesicles?
Linear- quanta are directly related to number of vesicles fusing
Experimenting with 4-aminopyridine that blocks voltage-gated K+ channels, what is the effect on depolarization? What does this mean for the number of synaptic vesicles released?
Prolonged depolarization
More synaptic vesicles released
When the motor axon is stimulated, the synaptic vesicles wind up opening into where because they fuse with what?
Synaptic cleft
Plasma membrane
A mini in a neuron can be classified what 2 ways depending on what effect it has on the post-synaptic neuron?
Excitatory (mEPSP- mini excitatory post-synaptic potential)
Inhibitory (mIPSP- mini inhibitory post-synaptic potential)
The amplitude of a mini caused by a single synaptic vesicle is proportional to what?
Strength of synapse
The frequency of minis is proportional to what?
Number of synapses
The amplitude of depolarization curve comes in multiples of ____ content?
Quantal
In an excitatory or inhibitory mini in a neuron, what ion binds what molecule to cause vesicle fusion and release?
Ca+2
Synaptotagmin
Once a neurotransmitter is released, it crosses what to bind to what?
Synaptic cleft
Ligand-gated ion channel receptors
Binding of a neurotransmitter to a receptor causes a small net post-synaptic ____ for a mEPSP (mini excitatory post synaptic potential) or ____ for a mIPSP (mini inhibitory post synaptic potential).
Depolarization
Hyperpolarization
Does Ca+2 indicator bind free or bound Ca+2? During an action potential in an axon, there is a transient increase in what type of Ca+2?
Free (answer for both)
Injecting Ca+2 in the pre-synaptic side causes what change in membrane potential on what side? Does it cause an action potential on the pre-synaptic side?
Increase
Post-synaptic
No
What effect does injecting a Ca+2 chelator have on pre vs post synaptic membrane potential? What can be concluded from this experiment?
Pre-synaptic: no effect
Post-synaptic: no increase in membrane potential
Ca+2 isn’t required for pre-synaptic action potential, but is for post-synaptic action potential
Adding cadmium on the extracellular side does what to the Ca+2 channels? When cadmium is added, what happens to the pre-synaptic Ca+2 current and post-synaptic membrane potential? What can be concluded from this experiment?
Blocks them
Pre-synaptic current is decreased
Post-synaptic cell isn’t depolarized
Ca+2 comes from outside to inside on pre-synaptic side, triggering release of synaptic vesicles
Calcium can be imaged what 2 ways? How do they work? What does calcium imaging reveal about a cell?
Dye (fluorescence when Ca increases)
Indicator protein (bind to Ca, then fluoresce)
Reveals neuronal activity
Injecting Ca into the pre-synaptic terminal would cause what in the post-synaptic terminal?
Depolarization
What is the first step in synaptic transmission (caused by action potential on pre-synaptic neuron)?
Action potential causes opening of voltage-gated Ca+2 channels (located near synaptic cleft on pre-synaptic side)
What is the second step in synaptic transmission (what does Ca+2 bind to, and what happens then)?
Ca+2 binds to synaptotagmin, triggering release of synaptic vesicles
What is the third step in synaptic transmission (what do the vesicles do)?
Vesicles fuse to plasma membrane
What is the fourth step in synaptic transmission (what does vesicle fusing release and where)?
Neurotransmitters are released into synaptic cleft
What is the fifth step in synaptic transmission (where does the neurotransmitter go and what does it bind to)?
Neurotransmitter diffuses across synaptic cleft and binds to receptor
What is the sixth step in synaptic transmission (what opens on the receptor and what does this cause)?
Gated channels on receptor open up, letting ions pass through
What is the seventh step in synaptic transmission (ion flow causes what?)
Ion flow through channels causes post-synaptic depolarization
What is the eighth step in synaptic transmission (what happens with the post-synaptic depolarizations, and what does that mean for the post-synaptic cell)?
Post-synaptic depolarizations get summed up- if they surpass threshold, an action potential occurs in the post-synaptic cell
What is the ninth step in synaptic transmission (what happens to the vesicle after it has fused and released its neurotransmitters)?
Vesicle gets recycled
What is the tenth step in synaptic transmission (what does the recycled vesicle fuse with)?
Recycled vesicle fuses with endosome
What is the eleventh step in synaptic transmission (what is the recycled vesicle filled with and what does this mean for the cycle of synaptic transmission)?
Vesicle is filled with neurotransmitter, starting cycle over
In the context of vesicles, what do exocytosis and endocytosis mean?
Exocytosis: release of vesicles
Endocytosis: taking vesicles in for recycling
What are 2 reasons why vesicles are recycled?
- Prevention of pre-synaptic plasma membrane enlargement
2. Energy conservation (energetically expensive to synthesize vesicles)
Budding off of the synaptic vesicle involves uncoating of vesicle from what molecule?
Clathrin
About how long does it take to make and recycle a vesicle?
1 minute
In anchoring, vesicles are stored in what? What molecule keeps vesicles away from the plasma membrane?
Reserve pool
Synapsin
In docking, where are vesicles brought close to? Are they close enough to fuse?
Plasma membrane
No
In priming, vesicles prepare to do what?
Fuse with the plasma membrane
During what step of synaptic vesicle life cycle does accidental fusion happen? What does accidental fusion cause?
Priming
Accidental fusion causes minis
In fusion, what molecule binds Ca+2 and enables fusing of vesicles to plasma membrane?
Synaptotagmin
In endocytosis, recycling and budding of vesicles is mediated by what protein?
Clathrin
In budding, what protein pinches off budding vesicles in order to release them?
Dynamin
In uncoating, vesicle loses its ____ coat and fuses with the ____. After this step, the vesicle is refilled with ____ and then ____ off the endosome. What happens to the vesicle’s life cycle then?
Clathrin Endosome Neurotransmitter Buds Starts over
What is the name of the proteins involved in vesicle fusion? What are they called if they are on the vesicle, and what are they called if they are on the target plasma membrane?
SNARES
vSNARES
tSNARES
What are the 2 vSNARES?
Synaptotagmin
Synaptobrevin
What are the 2 tSNARES?
Syntaxin
SNAP-25
Interaction of vSNARES and tSNARES is necessary for what process?
Docking
Which vSNARE binds after the SNARE complex is formed in docking?
Synaptotagmin
What happens to synaptotagmin once Ca+2 has bound to it?
Undergoes conformational change, enabling membrane of vesicle and plasma membrane to fuse
Primed vesicles with SNARE complexes formed are called ____ _____.
Ready releasable
Botulinum toxins function as what?
Proteases
What is the effect of toxins cutting SNARES?
Prevention of vesicle fusion
BotX-A is also called ____. What SNARE does it cut, and what is the effect?
Botox
SNAP-25
Blocks skeletal muscle contraction of face (limp paralysis), reducing wrinkles
Tetanus toxin cleaves what SNARE? It predominately affects what type of neuron? What do these neurons normally do, so what is the effect of this toxin?
Synaptobrevin
Inhibitory interneurons
Normally inhibit muscle contraction, so permanent contraction (lockjaw) occurs
The nicotinic acetylcholine receptor is gated by what? Is it voltage dependent?
Acetylcholine
No
The nicotinic acetylcholine receptor opens when what binds and closes when that molecule does what?
Acetylcholine
Comes off
The nicotinic acetylcholine receptor passes what 2 ions according to their driving force?
K+
Na+
What occurs at the reversal potential for the nicotinic acetylcholine receptor (nAChR)? Where is that potential relative to the equilibrium potentials of Na+ and K+?
Current switches directions
Somewhere in between equilibrium potentials for Na+ and K+
When a channel lets more than one ion through, it is important to think in terms of ____ current.
Net
At or below the equilibrium potential for K+, the net current of the nAChR is ____ and completely due to ___.
Inward
Na+
Below the reversal potential for the nAChR, the net current is ____ and is due to some ____ current, but more ___ current. The influence of ____ is increasing and the influence of ____ is decreasing.
Inward K+ Na+ K+ Na+
At the reversal potential for the nAChR, the net current is ____ and the Na+ and K+ currents are ____ and ____.
0
Equal
Opposite
At or above the equilibrium potential for Na+, the net current of the nAChR is ____ and completely due to ___.
Outward
K+
For both equilibrium potential (Ex) and reversal potential (Erev), when Vm is greater, the current flows ____. When Vm is less, the current flows ____. When Vm is the same, there is ___ net current.
Outward
Inward
No
In inward current, the cell becomes more ___. This is also referred to as _____ of the cell.
Positive
Depolarization
In outward current, the cell becomes more ___. This is also referred to as ____ of the cell.
Negative
Hyperpolarization
When the outside concentration of Na+ is decreased, what happens to the equilibrium potential of Na+ and the reversal potential?
Equilibrium potential and reversal potential are decreased
When the outside concentration of K+ is increased, what happens to the equilibrium potential of K+ and the reversal potential?
Equilibrium potential and reversal potential are increased
How can the end plate current be calculated from the conductance of the AChR channel, its Vm, and its Erev?
End plate current = g of AChR (Vm-Erev)
How does determining the direction of current differ when using equilibrium potential vs reversal potential?
Equilibrium potential is determined for a single ion, whereas reversal potential is determined as a net current from all ions
4 ways to increase the amplitude of a mini (or post-synaptic Vm): neurotransmitters, vesicles released, Ca, and receptors
- Increase amount of neurotransmitter released
- Increase number of vesicles released
- Increase pre-synaptic Ca
- Increase number of receptors on post-synaptic side
Synaptic potential is caused by the opening of what type of channels? Action potential is caused by the opening of what type of channels?
Ligand-gated ion channels
Voltage-gated Na+ and K+ channels
Reversal potential depends on what 2 things (think I= g x DF)?
Channel conductance
DF of ions involved
If reversal potential is above threshold, stimulating the channel results in a ______ in the post-synaptic neuron, also referred to as an _____ response.
Depolarization
Excitatory
If reversal potential is below threshold, stimulating the channel results in a ______ in the post-synaptic neuron, also referred to as an ______ response.
Hyperpolarization
Inhibitory
If the reversal potential is greater than Vrest but lower than threshold, the post-synaptic neuron will become _____, but (will/will not) reach threshold.
Depolarization
Will not
Is one depolarization from an excitatory neuron enough to cause an action potential?
No
What effect does an inhibitory pre-synaptic neuron have on the total excitation of the post-synaptic neuron? What does that mean for an action potential of the post-synaptic neuron?
Decreases total excitation
May prevent action potential by preventing total excitatory inputs from reaching threshold
In an electrical synapse, speed is limited only by what?
Rate of diffusion
When Ca+2 channels are blocked, can any vesicle fusion occur and why?
Yes- even though induced fusion no longer occurs, spontaneous fusion still can
