BioNB 442: Lab 6

Active cell model


You will build a simple, active model of a neuron with variable sodium and potassium conductances, then use use Matlab programs to probe the electrical characteristics of the model.



  1. Modify slowAIni.m to include uicontrol edit fields for dt and max time. Add uicontrol buttons to start plotting voltages and to quit the program. You should be able to start the plotting several times (perhaps after adjusting the time parameters) without restarting the program.
  2. Build Circuit 1 above and use your modified program to record some voltage traces. For each of the manipulations below, describe what you see. Include all voltage recordings in your report.
    1. Vary only the sodium conductance over its full range. Set potassium to minimum conductance (ccw). Repeat with potassium set to maximum conductance (cw).
    2. Vary only the potassium conductance over its full range. Set sodium to minimum conductance (ccw). Repeat with sodium set to maximum conductance (cw)
    3. Generate a waveform which resembles an action potential with positive overshoot caused by a large sodium conductance, followed by a hyperpolarization caused by increased potassium conductance (and low sodium conductance).
  3. Build Circuit 2 above by slightly modifying the existing circuit. Be sure to set the two potentiometers to max conductance. Further modify your program to produce a 1 second long 5 volt pulse about 4 seconds after the program starts recording voltage. For each of the manipulations below, describe what you see. Include all voltage recordings in your report.
    1. What is the time constant of the model cell with both switches open?
    2. Start the trace and after about 1 second, turn on the potassium switch. What happens to the stimulus amplitude. Why? Measure the cell time constant just after you turn on the switch, then again just after you turn off the switch. What are the values and why are they different?
    3. Simulate an voltage-triggered action potential by waiting for the stimulus pulse then flipping switches.
    4. Set the sodium potentiometer to 50% and repeat 3. This condition might correspond to poisoning half the channels with TTX.
    5. Increase the membrane capacitance to 100 uf. and repeat 3.

Your written lab report should include:

  1. Your programs
  2. Circuit schematics
  3. Screen shots of the various waveforms you recorded.
  4. Descriptions of circuit behavior


Simple Analog Models to Teach Electrophysiological Concepts, Ferit Pehlivan, Proceedings of the 2005 IEEE Engineering in Medicine and Biology 27th Annual Conference, Shanghai, China, September 1-4, 2005, pp 863-866 (Cornell students who are logged on using campus networks can seach for the title on Google and get the full text. Cornell students who are logged on off-campus must use the library interface and search for IEEE Xplore, then search for the title.)

June 2007 Copyright Cornell university