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21 Cards in this Set
- Front
- Back
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What is the resting membrane potential? |
Resting membrane potential (Vm) is typically around -70 mV |
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What is the resting membrane potential determined by? |
Principally determined by Na+ and K+ |
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What is the equilibrium potential for a cell? |
The equilibrium potential for an ion is the membrane voltagethat a cell needs to be at to prevent movement of that iondown its concentration gradient. •If inside is very negative it will stop K+from leaving •If inside very positive it will stop Na+from entering |
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What are the EK and ENa values for physiological concentrations? |
For physiological concentrations Nernst eqn showsEK = -90 mV and ENa = +50 mV |
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Why are these values -90 and +50? |
Cell needs to be at -90 mV to stop K+ leaving and+60 to stop Na+ entering |
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Why is Vm much closer to EK? |
Vm much closer to EKthan ENa because membraneabout 50 times more permeable to K+than Na |
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Why is net flow of ions zero at constant Vm? |
At constant Vm net flow of ions is zero because thepassive leak of K+ out is matched by leak of Na+in |
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What happens if a cell becomes permeable to an ion? |
If a cell becomes permeable to an ion then that ionwill move down its electrochemical gradient and willdrive Vm towards the equilibrium potential for that ion |
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What is the driving force on an ion? |
Driving force on ion = Vm - Eeq •For Na+= -70mV – (+50mV) = -120 mV |
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What does the Golman Hodgkin Katz equation consider? |
• Nernst eqn deals with one ion at a time and makes noassumptions about relative permeabilities • Goldman Hodgkin Katz eqn considers relativepermeabilities of monovalent ions |
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What is the Golman Hodgkin Katz equation? |
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What are the properties of an action potential? |
1. Triggered by depolarisation 2. Threshold of depolarisation required for AP 3. All or none 4. Propagates without decrement 5. At peak : Vm approaches ENa 6. After AP membrane is inexcitable duringrefractory period |
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What is the action potential caused by? |
Action potential due to current flowthrough voltage-gated sodium andpotassium channels |
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What are channels selective for? |
Channels are highly ion-selective |
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What is the probability of channels opening or closing determined by? |
• Channels are open or closed • Probability of opening and closing isdetermined by the voltage across thechannel |
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What happens to the membrane potentials durimg the action potential? |
• If a cell becomes permeable to an ion thenthat ion will move down its electrochemicalgradient and will drive Vm towards itsequilibrium potential • During the action potential membrane becomespermeable to sodium first and then potassium • Membrane is driven to ENa and then EK |
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What happens when there is prolonged depolarisation? |
Prolonged depolarisation causes sodium inactivation |
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What is charge equal to? |
Charge Q (coulombs) = capacitance C x voltage V |
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How much charge does each mole of a monovalent ion have? |
Each mole of a monovalent ion has 10^5 coulombs of charge |
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What happens if there is 1 picomole per cm2 for 100mV ? |
1 picomole per cm2for 100mV • Very few ions need to be separated • Negligible osmotic consequences |
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How is the action potential propogated? |
The action potential generated at the axon hillockpropagates as a wave along the axon. The currents flowing inwards at a point on the axon during anaction potential spread out along the axon, and depolarize the adjacent sections of its membrane |
