1. Without changing any other parameters, vary the duration (pulse width) in the stimulation panel between 10 µs and 1 ms in steps. Find the threshold current that is barely enough to initiate an action potential for each stimulus duration. You might want to use smaller steps at smaller durations for better resolution since the curve will be steep for small pulse widths.
For instance: Use steps of 10µs, from 10µs to 50µs, and then steps of 50µs from 50µs to 300µs and then steps of 100µs after. You need to search for the threshold by varying the amplitude and running the simulation again and again to find the threshold accurately. Try to get enough precision in amplitude so that your curve looks smooth. Also, make sure to apply a very long pulse at the end (e.g. 5ms) to find the rheobase current accurately.
2. Write down your threshold amplitude and duration values in a table and enter into an mfile. Plot the current versus duration. This is called strength-duration curve.
3. Now, reset the parameters to initial values, and try another axon diameter in the simulation software to see how activation threshold changes by the axon diameter.
Try a twice larger and a twice smaller diameter and use a single pulse duration, e.g. 0.2ms. Does the threshold increase or decrease with axon diameter?
4. Finally, increase and decrease the intracellular and extracellular concentration of the sodium, potassium, and chloride ions (one at a time) and report how these changes affect the resting potential of the cell.
You may want to use a table to present this info.