BIO325 Laboratory Guide #13 (2024)

 

ACTION POTENTIALS V:

COMPUTER SIMULATIONS OF ACTION POTENTIAL

PROPAGATION
The writeup for this lab
falls under category
C

 

 

This set of simulations will allow you to explore the mechanisms of propagation of action potentials down axons. The simulations are part of the Neurons in Action set by Moore and Stuart. In this set you will work through three tutorials on the unmyelinated axon, myelinated axon, and partially demyelinated axon.

 

I. UNMYELINATED Axon Tutorial

 

Launch NIA2 from your C: drive and select The Unmyelinated Axon tutorial. Read throught the introductory materials then Start the tutorial.  In the course of the first few exercises, refamiliarize yourself with the window controls, especially:

 

            a) opening and manipulating parameter windows

            b) opening, resizing, and positioning display windows

            c) rescaling display window plots

            d) erasing individual traces in a plot

            e) arranging and printing and printing windows

 

Work through this entire tutorial.


Data Sheet Item #1a:

Produce a well-labeled printout which compares AP wave shapes plotted as functions of time and distance. A 5 msec. quad time trace and a 50,000 mm spatial trace frozen partway through the AP is a good way to do this.

Data Sheet Item #1b:

Produce well-labeled printouts which demonstrate that axons conduct APs equally well in both directions.



     


Data Sheet Item #2a:

Produce printouts for at least four different axon diameters from which you can calculate conduction velocities.

Data Sheet Item #2b:

Use Excel to produce a plot of conduction velocity as a function of axon diameter.



    

Q1:      Can you relate your results for this simulation to your findings on axon cable properties from the earlier labs, involving computer and electronic simulations of passive axon membrane..  Think specifically about how current spread relates to voltage decay with distance in passive membrane, and how these properties vary with axon diameter.  How does the space constant l of an axon relate to rate of action potential propagation?

 

When you are finished, Quit the tutorial.

 

 

II. Myelinated Axon Tutorial

 

Select and Start The Myelinated Axon tutorial.

 

Work through this entire tutorial.


Data Sheet Item #3a:

Produce printouts of APs from which you can measure conduction velocities for at least four different numbers of myelin layers.

Data Sheet Item #3b:

Use Excel to produce a plot of conduction velocity as a function of number of myelin layers.





Data Sheet Item #4a:

Produce printouts of APs from which you can measure conduction velocities for at least four different temperatures

Data Sheet Item #4b:

Use Excel to produce a plot of conduction velocity as a function of temperature.



         

Q2:      Again, can you relate your results for this simulation to your findings on axon cable properties from the earlier lab, involving an electronic simulation of passive axon membrane.  Think specifically about how current spread relates to voltage decay with distance in passive membrane, and how these properties vary with membrane capacitance.  How does myelination of the internodal space affect the space constant l of an axon and how to this relate to rate of action potential propagation?

 

 

When you are finished, Quit the tutorial.

 

 

III. Partial Demyelination Tutorial

 

Select and Start the Partial Myelination tutorial.

 

Work through this entire tutorial.

 


Data Sheet Item #5:
Produce a set of printouts and a plot which investigates one parameter which influences the ability of an AP to invade a demyelinated region of an axon.


         

Q3:      Can you relate your results for this simulation to what you know about the pathology

            or symptoms of demyelinating diseases, such as poliomyelitis, multiple sclerosis (MS), or amyotrophic lateral sclerosis (ALS)?

 

 

IV. ADDITIONAL TutorialS

 

If you have time, explore the Axon Diameter Change and Nonuniform Channel Density tutorials.  These tutorials will give you a much richer understanding of some additional widespread phenomena that can make real neurons behave rather differently than simplified views and models of neurons might suggest.

 

 

      V.  PREPARATION OF THE LAB DATA SHEET


Your data sheet should include all FIVE of the items described in the boxes above.

Make sure that the axes of all of the graphs and print-outs are labeled and calibrated. You should certainly discuss your results and the answers to the questions with your partners and others in the lab. However, please work independently when you prepare your data sheet.

 

The writeup for this lab
 falls under category
 C