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Exam 3
Unit 1
25
Other
Undergraduate 4
11/15/2016

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Term
Julius Bernstein
Definition
early 1900's - proposed the "membrane breakdown" hypothesis to explain change in membrane potential
Term
Was Bernstein's "membrane breakdown" hypothesis rigorously tested?
Definition
not until 1940's by Hodgkin & Huxley
Term
Who published the first figure of the intracellularly recorded action potential?
Definition
Hodgkin & Huxley
Term
Was the first intracellular recorded action potential figure supportive of or contradictory to Bernstein's "membrane breakdown" hypothesis?
Definition
extremely contradictory
Term
What hypothesis was supported by the first figure of the intracellular action potential?
Definition
the sodium hypothesis
Term
The first intracellular recorded action potential refuted ______ & supported ______
Definition
refuted Bernstein's hypothesis & supported the sodium hypothesis
Term
What explanation was given for the fact that the membrane potential goes above 0 in an action potential?
Definition
sodium conductance >>>>> potassium conductance
Term
2 things you must have in order to have a resting membrane potential
Definition
1. concentration gradients
2. selective permeability
Term
How did Hodgkin & Huxley test the sodium hypothesis?
Definition
change the outside concentration of sodium - if the rising phase of the AP is due to sodium, this would affect it
Term
What was the proposed relationship between membrane potential & conductance?
Definition
membrane potential changes the conductance --> increase in conductance causes a change in membrane potential
Term
What technique was needed to test AP current?
Definition
voltage clamp
Term
Why was using an electrode an issue for Hodgkin & Huxley?
Definition
this was before the invention of the glass electrode
Term
Why did Hodgkin & Huxley use a squid giant axon for testing their AP hypothesis?
Definition
allows insertion of a small wire down the axon
Term
Did Hodgkin & Huxley's wire cross the membrane of the squid giant axon?
Definition
NO!
Term
isopotentiality
Definition
the voltage (membrane potential) is the same throughout the neuron
Term
Why is isopotentiality an issue when studying an axon?
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
Term
What was the solution to the axon isopotentiality issue?
Definition
got an electrode to go down entire axon (not just one end)
Term
Was speed an issue for Hodgkin & Huxley?
Definition
yes!
Term
variable value battery
Definition
current flows down wire to charge membrane & keep membrane potential at a set value
Term
Why do you need a voltage clamp?
Definition
you need a computer to regulate the variable value battery because it needs to work very fast
Term
What is the catch 22 when using the voltage clamp wire?
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
Term
H&H were able to show that AP current is carried by _____ & ______ currents using voltage clamp technique in the squid giant axon preparation
Definition
sodium & potassium
Term
In Hodgkin & Huxley's experiments, what two voltages equaled each other?
Definition
V inside cell = V of battery
Term
How did Hodgkin & Huxley solve the big problem of the small wire having resistance meaning there is a voltage drop?
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)
Term
What was the role of the voltage clamp amplifier in Hodgkin & Huxley's experiments?
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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