Action Potentials can be a Puzzle

I found myself digging through a closet of scrap-booking goods last night in a frantic effort to find a 1 3/8” hole punch. I had been sparked by an idea that has been percolating for years, but I’ve never implemented. I wanted to build a cell with ions, channels, and charges so my students could manipulate the “players” involved in the resting membrane potential and an action potential.

This concept is particularly challenging for students. They could use chemistry, biology, and elements of physics to understand this system, but mine are woefully under prepared. Their eyes glaze over when they have to think about electrical gradients and chemical gradients working simultaneously. Add in channel types and applications to graphs that describe membrane changes in voltage, and even I’m starting to have an anxiety attack! When I teach this concept, the energy in my classroom is so thick, I could cut it with a knife. There has to be a better way.

berfore-ap
Before…

But so far, no amount of restructuring, dividing, or attempting to present just a “snapshot” in time had worked to facilitate the connection between what is occurring with ions and how it happens. So I cut out a giant cell, a little positive and negative sign, and all the different channels, and put them in a bag. That handy scrapbook punch allowed me to make sets of 10 potassium ions and 10 sodium ions in the colors I have been trying to get my students to associate with this concept. Voila- my students will now have an intracellular space on a table that represents the extracellular space…and all the important pieces as well.

before-ap
…and after.

Back in the classroom, as I drew on the board a picture of each step of the electrical changes experienced by the cell, they had to manipulate their cell. Did it work dreamily well? Probably not. Some students got it and visibly relaxed. But some students didn’t get it…and remained in a state of panic. However, I did discover that my students were pretty mixed up by the concepts of “depolarization” and “repolarization.” Because they can’t see the cell, sometimes this creates a mental block.

After class, a subset of students followed me to my office, where we played more with the model and I’ll be darned if they didn’t get to the point where they could set up their cell appropriately for each of the phases of the action potential! I could ask questions like, “Can the cell be stimulated again at this point?” And the question I love more, “WHY!?!” Light bulbs started turning on and several students took pictures so they could make their own model at home to use while studying.

This week in lab we use the HHsim program to study action potentials and this time, my new models will be on the table with them and they are going to have to show me what happens to explain the graphical results they get. My hope is that time, coupled with this paper model, will help them master the concepts.


Nichole Warwick teaches biology at Clatsop Community College and is a proud member of the HAPS Communications Committee.

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