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50 Cards in this Set
- Front
- Back
What are two major types of chemical transmission? |
Direct and indirect |
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What is the best system to study direct receptors? |
The neuromuscular junction |
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What are the benefits of studying the neuromuscular junction? |
The muscle cell is large enough to accommodate several microelectrodes for electrophysiological measurements Postsynaptic membrane can be visualized with the light microscope in a living cell Muscle fiber is innervated by only one motor axon |
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What is the transmitter released at the neuromuscular junction? |
ACh |
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What receptor type is in the muscle membrane? |
The nicotinic type of ACh receptor |
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What is the end-plate? |
The motor neuron's axon innervates this specialized region of the muscle membrane |
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Does the axon have myelin at its end? |
No |
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Does the axon branch? |
Yes |
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What are synaptic boutons? |
Multiple grape-like varicosities that are the ends of the branches of the axon, where transmitter is released |
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What are junctional folds? |
A depression in the surface of the muscle fiber where the membrane of the muscle fiber forms deep folds; corresponds to a bouton |
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What is the basement membrane?
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Basal lamina; lines the junctional folds; a network of connective tissue consisting of collagen and glycoproteins that covers the surface of the entire muscle fiber
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Which cell secretes secretes proteins into the basement membrane? |
Both the presynaptic and muscle cell |
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Describe acetylcholinesterase. |
Enzyme that inactivates the ACh released by the presynaptic terminal by hydrolyzing it to acetate and choline |
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What organizes the synapse? |
The basement membrane |
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What machinery is required in the presynaptic bouton to release transmitter? |
1) Synaptic vesicles, which contain ACh 2) Active zone, a membrane specialization 3) Voltage-gated Ca2+ channels |
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What is the function of calcium in the presynaptic terminal? |
It triggers the fusion of the synaptic vesicles with the terminal |
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What part of the presynaptic terminal is apposed to the junctional fold? |
The active zone |
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Characterize the crest of the junctional fold. |
Receptors for ACh are clustered |
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Describe the depths of the folds. |
Rich in voltage-gated Na+ channels, which convert the end-plate potential into an action potential |
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What is the name of the excitatory postsynaptic potential at the neuromuscular junction? |
End-plate potential |
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What is the amplitude of the endplate potential? |
70 mV |
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What is the amplitude of the typical synaptic potential from a single neuron? |
Less than 1 mV |
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What would you use to block ACh channels? |
Curare |
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What is the purpose of adding curare to the NMJ? |
To reduce the end-plate potential so that it doesn't trigger an action potential |
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What are the kinetics of the NMJ response to a subthreshold end-plate potential? |
Rises rapidly but decays more slowly |
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What two processes act quickly to remove ACh from the cleft? |
1) ACh is hydrolyzed by the acetylcholinesterase 2) ACh diffuses away, out of the synaptic cleft |
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How can you determine which ions move through the membrane to produce synaptic action? |
By systematically changing the membrane potential and determining the reversal potential for synaptic action |
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What is reversal potential? |
The membrane potential at which the synaptic potential or synaptic current has zero amplitude |
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What is the equation for current of the excitatory post-synaptic potential?
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Iepsp = gepsp x (Vm - Eepsp)
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What is the reversal potential for the end-plate? |
0 mV |
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What determines the reversal potential for the end-plate? |
A weighted average of ENa and Ek |
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How do Na+ and K+ transmitter-gated and voltage-gated channels differ in the NMJ? |
1) Move through different classes of voltage-gated channels, one for each, activated sequentially; the ACh-activated channel is large enough for either to pass with equal selectivity, also Ca2+ 2) Na+ flux in the voltage-gated channels is regenerative, ACh channel activation is limited by the amount of ACh available and cannot produce an all-or-none action potential 3) Pharmacological differences, TTX blocks voltage-gated Na+ but not transmitter-gated, alpha-bungarotoxin blocks ACh receptors only |
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What determines the reversal potential? |
1) Relative conductance for the permeant ions 2) The equilibrium potentials of the ions |
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What two things are balanced at the reversal potential? |
INa + Ik = 0 |
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Describe a double-gated channel. |
NMDA receptor, both chemically and voltage gated |
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What technique would you use to measure the current through a single ACh-activated channel? |
Patch-clamp |
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What effect does changing the driving force have on the current? |
The magnitude of the current through the channels |
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What is the equation for total synaptic conductance? |
gEPSP = n x gamma where n is the average number of channels opened, defined by n = N x po where po is the propability that any given ACh channel is open and N is the total number of ACh channels |
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What is the equation for total end-plate current? |
IEPSP = N x po x gamma x (Vm-EEPSP) |
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What four factors does the current for the end-plate potential depend on? |
1) The total number of end-plate channels 2) The probability that a channel is open 3) The conductance of each open channel 4) The driving force that acts on the ions |
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What determines the probability that a transmitter-gated channel is open? |
The concentration of the transmitter at the receptor, not the value of the membrane potential |
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What two functions does a directly gated receptor-channel have? |
1) It recognizes and binds the chemical transmitter 2) It opens a channel in the membrane through which ion flows |
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Which subunit of the nicotinic ACh receptor binds ACh? |
Alpha |
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What determines the cation-selectivity of the nicotinic receptor? |
Three rings of negative charge that flank the M2 region |
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What are the three regions of the receptor-channel complex? |
1) A large entrance region at the external membrane surface 2) A narrow transmembrane pore that may determine cation selectivity 3) A large exit region at the internal membrane surface |
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What is the net effect of the opening of nicotinic ACh receptors? |
Net influx of Na+ ions |
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What are the three parallel regions of the end-plate equivalent circuit? |
1) A branch representing the flow of synaptic current through the transmitter-gated channels 2) A branch representing the return current flow through nongated channels (the nonsynaptic membrane) 3) A third branch representing current flow across the lipid bilayer, which acts as a capacitor |
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What are two parallel pathways for outward current flow? |
1) Nongated channels 2) Capacitive pathway |
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What is the equation for membrane voltage? |
(gEPSP x EEPSP + gm x Em) / (gEPSP + gM) |
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What is the equation for the amplitude of the end-plate potential? |
deltaVEPSP = Vm - Em |