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homework1ans - BME665/565 Notes on Assignment 1 Overall:...

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BME665/565 – Notes on Assignment 1 Overall : Most people provided a good explanation of why they saw the results they did. On a test, an answer without such an explanation would be insufficient for a passing grade. Also, the questions were mis-numbered, so that part of question 6 appeared as a second part of question 5, and part of question 5 appeared as the second half of question 4. So… if you answered all of 4, you answered part of 5 too! 1) Test the hypothesis that the action potential is an "all-or-none" event. i.e. that there is a critical level of stimulus that results in an action potential - below that level no action potential is generated, above that level no further change in the amplitude of the action potential occurs. Draw a graph of action potential amplitude vs. stimulus amplitude. Related question: Even if the amplitude of the action potential does not change with increasing stimulus amplitude above threshold, do any other characteristics? The expected behavior of a typical HH neuron (using parameters from class) is that as current is injected, sodium channels are activated – if enough current is injected, lots of sodium flows into the neuron and a spike occurs. The all-or-none behavior is predictable from the Hodgkin-Huxley equations – once the membrane is depolarized to a certain level (by the current injection), the sodium channels become activated and the currents start to flow into the cell, further depolarized the neuron and creating a positive feedback loop. Below that level, we are “off the curve”, so to speak – the membrane potential is not sufficient to cause sodium to flow into the cell. Most people who answered this question confirmed the “all-or-none” property of the action potential by injecting currents of different sizes into a typical HH neuron and plotting the maximum membrane potential that results. A number of people also noted that the delay to
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This note was uploaded on 04/04/2010 for the course BME 302L taught by Professor Maarek during the Spring '08 term at USC.

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homework1ans - BME665/565 Notes on Assignment 1 Overall:...

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