Bill's Nerve Simulation

NOTE: This simulation is a DOS simulation, not a windows program. It will run in a DOS window as shown above. When it displays an action potential, the screen will switch to full-screen mode. I am working on a windows version. This figure shows the setup for the nerve simulation. Background information on the application can be read by pressing F10, an explanatory picture is at F9.  You can start the nerve simulation by clicking here and telling the pop-up box to run the program from it's current location.

1. NOTE: if the simulation doesn't run when you press the button, choose "save the program to disk", choose a directory (remember it), open Windows Explorer (not Internet Explorer), click over to the window, and then double-click on nerve.com. It should run fine then.

2. When this window (click to make larger) opens, tell it to run.

3. On some versions of XP you will get a message concerning the 16 bit MS-DOS Subsystem (whatever that is). Just tell it to ignore the problem and it'll run fine. I'm not sure that it will run at all under Vista (after all, nothing else does). That window will look like this: (Click to enlarge)

4. Sorry it looks so clunky. Look's like it needs a re-write....

Here, a multiple stimulus simulation is selected.

Two stimuli are selected here.

This figure shows the components of an action potential and portions of the screen.

Here's the results of a single stimulus of 10 mV for a 1 mV duration. Try decreasing the stimulus duration while holding the voltage constant until you no longer get an action potential. At that point, increase the stimulus voltage.

By only slightly reducing the input voltage to 8 mV, the nerve cell never reaches threshold. Increase the stimulus duration until you get an action potential (leave the voltage at 8 mV)

In multiple stimulus mode, an 8 mV stimulus applied at 2 ms intervals never results in an action potential.

Decreasing the pulse interval while holding the voltage at 8mV will produce action potentials. Increase the pulse interval to 1.5 ms. Explore what happens if you increase the stimulus voltage. What happens if you decrease the pulse interval?

Effects of inhibition on nerve cell function. In this simulation, an inhibitory impulse (-20 mV) is followed by a previously successful 10mV, 1ms stimulus. No action potential is seen.

An action potential is not seen until you allow an 8 ms interval between the inhibitory pulse and the 10 mV, 1 ms stimulus.

A stronger stimulus will permit an action potential.

The Nerve Lab (You can get a print-out here)

This simulation will allow you to explore the effects of stimulus voltage, duration and frequency on a model nerve cell. If this is your first time using the simulation, press the <F10> function key for help or ask your instructor for assistance. Otherwise, provide inputs for questions in the above menu.

You must first choose either the multiple stimulation mode or the single stimulus mode. The single stimulus mode produces a voltage pulse that like this:"___▒___", while the multiple stimulus mode produces a chain of pulses:"_▒__▒__▒__▒__▒__▒_". In either mode, you can adjust the stimulus intensity in millivolts (mV): You can also adjust the stimulus duration in milliseconds (ms):

 Short duration: __▒__ Longer duration: __▒▒▒▒▒▒▒▒__

 The multiple stimulus mode also allows you to vary the frequency:

 Low frequency: ___▒_____▒_____▒___ High Frequency: _▒__▒__▒__▒__▒_

How to begin
If this is your first time using the program, begin with the single stimulus mode (answer "N" to the first question. Then begin with 20 mV stimulus amplitude at .5 ms stimulus duration. Enter "N" to the next question (you don't want to enter a second stimulus). The screen will then switch to a display similar to the following:

1.       Determine what a normal action potential looks like, and what stimuli are required to produce an action potential. (Start with 20 mV at 0.4 ms).

2.       Experiment with varying the stimulus amplitude while holding the duration constant  (keep the duration at 0.4 ms and try a lower voltage (like  10  mV). Does the nerve still respond with an action potential?  Decrease the stimulus  amplitude  and determine the threshold voltage for  a  0.4   ms duration stimulus. Try increasing the stimulus voltage above 20 mV.  Does the resulting action potential look more-or-less the same?

3.       Next  vary  the stimulus duration.  Start with a stimulus amplitude near, but  below  threshold (as determined in (2))  and step  up  the  stimulus duration. Does an increase in stimulus duration allow an action potential to occur for what was previously a sub-threshold stimulus? The remaining experiments rely on the use of the dual stimulus mode and multiple stimulus modes.

4.       Demonstration of Absolute and Relative refractory periods. To demonstrate the absolute refractory period, choose the single stimulus mode and enter a stimulus at or near threshold (say,  20  mV at 0.4  ms).  Then indicate that  you  need  to enter another stimulus.  Enter your  second  stimulus parameters (for example,  20 mV at .4 ms)  with an interpulse interval of  only 3.0  ms or so).  Since the second stimulus arrives during the active    phase  of  the  action  potential,  the nerve does  not  respond  to  the  stimulus.   Increase the amplitude of the second stimulus by  an order of magnitude  (keep  the first stimulus as 20  mV for 0.4  ms and allow  the second amplitude  to  be 200  mV).  Note that the nerve still  does  not  respond  indicating  that you are attempting to stimulate it  during  the absolute  refractory period.  Increase the interpulse interval until  you can  get a response to the second 200  mV stimulus.  If the cell does not  respond  to  a  20   mV stimulus for those  conditions,   then  you  have  demonstrated the relative refractory period.

5.       Next   use the  multiple stimulus  mode to  demonstrate the   effects  of stimulus frequency on the nerve impulse.  Choose a subthreshold condition (such  as  5 mV at .4  ms)  and change the interpulse  duration (shorter durations result in higher frequencies).