BME 5401 - BME 5401/BME4409 Homework 2. Due Sept 19 in...

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BME 5401/BME4409 Homework 2. Due Sept 19 in class PART A BOX your answer Consider a cell with the following ion concentrations (mM): [Na] out = 118, [Na] in = 15, [K] out = 9, [K] in = 150. Compute: 1. Nernst potential for Na (E Na ) 2. Nernst potential for K (E K ) Using the classic electrical circuit model for the passive Na and K membrane channels with R Na = 3.5 X 10 8 ohms and R K = 2.0 x 10 5 ohms and the Nernst potentials from Questions 1 and 2, compute: 3. leakage current 4. membrane potential PART B Box your answers Download the Hodgkin-Huxley Simulator from: http://www.cs.cmu.edu/~dst/HHsim/ . (Downloading Matlab code will create folder "hhsim_31_source". Run Matlab with this as the current directory). Click on the Channels button in the main window to call up the Channels window. In the Channels window, turn off all the channels except the first one (passive sodium), by clicking on their respective buttons. Notice that the resting potential Vr displayed in the Membrane window is now equal to the Nernst potential for sodium, 52.4 mV. A mouse click on the red line will show you the exact value of the membrane voltage. The membrane voltage may not be exactly equal to V r, but clicking the yellow Nudge button a few times will nudge things along until the voltage reaches the theoretical asymptote. Or you can click Run , wait a while, and then click Stop . 1. Calculate the effect of halving the external sodium concentration (still only sodium channels on). Use the simulator to confirm your answer by looking at the value of passive Vr in the Membrane window. (You can type new values into any of the boxes in the Membrane window, or use the < or > buttons to change the values.) 2. Calculate the [Na] external concentration required to achieve Vr = 55.5 mV. Confirm your answer using the simulator. 3. Suppose we double the temperature from 6.3 deg C to 12.6 deg C. What is the new value of V r ? Explain why Vr doesn't double. 4. Reset the simulator by typing "hhsim" again in the MatJab command window. Click the "Stim1" button to deliver a depolarizing current and elicit an action potential. Describe the actionpotential: (a) what's the peak voltage? (b)
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This note was uploaded on 02/06/2012 for the course BME 5401 taught by Professor Johannesvanoostrom during the Fall '10 term at University of Florida.

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BME 5401 - BME 5401/BME4409 Homework 2. Due Sept 19 in...

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