Term
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Definition
| early 1900's - proposed the "membrane breakdown" hypothesis to explain change in membrane potential |
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Term
| Was Bernstein's "membrane breakdown" hypothesis rigorously tested? |
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Definition
| not until 1940's by Hodgkin & Huxley |
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Term
| Who published the first figure of the intracellularly recorded action potential? |
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Definition
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Term
| Was the first intracellular recorded action potential figure supportive of or contradictory to Bernstein's "membrane breakdown" hypothesis? |
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Definition
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Term
| What hypothesis was supported by the first figure of the intracellular action potential? |
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Definition
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Term
| The first intracellular recorded action potential refuted ______ & supported ______ |
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Definition
| refuted Bernstein's hypothesis & supported the sodium hypothesis |
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Term
| What explanation was given for the fact that the membrane potential goes above 0 in an action potential? |
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Definition
| sodium conductance >>>>> potassium conductance |
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Term
| 2 things you must have in order to have a resting membrane potential |
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Definition
1. concentration gradients
2. selective permeability |
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Term
| How did Hodgkin & Huxley test the sodium hypothesis? |
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Definition
| change the outside concentration of sodium - if the rising phase of the AP is due to sodium, this would affect it |
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Term
| What was the proposed relationship between membrane potential & conductance? |
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Definition
| membrane potential changes the conductance --> increase in conductance causes a change in membrane potential |
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Term
| What technique was needed to test AP current? |
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Definition
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Term
| Why was using an electrode an issue for Hodgkin & Huxley? |
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Definition
| this was before the invention of the glass electrode |
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Term
| Why did Hodgkin & Huxley use a squid giant axon for testing their AP hypothesis? |
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Definition
| allows insertion of a small wire down the axon |
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Term
| Did Hodgkin & Huxley's wire cross the membrane of the squid giant axon? |
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Definition
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Term
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Definition
| the voltage (membrane potential) is the same throughout the neuron |
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Term
| Why is isopotentiality an issue when studying an axon? |
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Definition
| there is resistance to current flow in a long, thin cylinder; if you insert a wire & inject current, membrane potential recorded at different parts of the axon will be different from one another |
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Term
| What was the solution to the axon isopotentiality issue? |
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Definition
| got an electrode to go down entire axon (not just one end) |
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Term
| Was speed an issue for Hodgkin & Huxley? |
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Definition
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Term
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Definition
| current flows down wire to charge membrane & keep membrane potential at a set value |
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Term
| Why do you need a voltage clamp? |
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Definition
| you need a computer to regulate the variable value battery because it needs to work very fast |
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Term
| What is the catch 22 when using the voltage clamp wire? |
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Definition
| you have an electrode (a small wire that has some resistance) in the cell & you pass current through the wire, between the beginning & end of that wire you will get voltage; even though it is a good conductor, it doesn't have 0 resistance --> voltage at the end of the wire will be different from at the beginning |
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Term
| H&H were able to show that AP current is carried by _____ & ______ currents using voltage clamp technique in the squid giant axon preparation |
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Definition
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Term
| In Hodgkin & Huxley's experiments, what two voltages equaled each other? |
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Definition
| V inside cell = V of battery |
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Term
| How did Hodgkin & Huxley solve the big problem of the small wire having resistance meaning there is a voltage drop? |
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Definition
| inserting two wires! (first wire served as a recording electrode, second wire served as a current passing electrode to keep voltage at whatever they wanted it to be) |
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Term
| What was the role of the voltage clamp amplifier in Hodgkin & Huxley's experiments? |
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Definition
| to compare the command voltage with the actual membrane potential (actual voltage being recorded by the recording electrode) & then it would pass current through the current passing electrode to make sure that they stay the same |
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