This is an activity I created to illustrate the concepts of excitatory/inhibitory stimulation and triggering thresholds using a deck of playing cards.
Students form groups of 5: of these 4 students will play the roles of dendrites and one student will be the axon hillock, summing the messages received from the dendrites. The dendrites each receive a handful of face-down playing cards, while the axon hillock is told a number which represents the triggering threshold for firing an action potential.
Black suits (clubs and spades) represent excitatory stimulation (+), while red suits (hearts and diamonds) represent inhibitory stimulation (-). Aces count as +1 or -1, and face cards count as either +10 or – 10, depending on the suit.
On “Go!” all the dendrites turn their top cards over and the axon hillock must quickly determine whether the triggering threshold has been met by summing the total value of the cards shown. For instance, if the threshold for firing was +5 and the revealed cards were 5H, 7S, 3C, and 8D, the answer would be “Don’t fire!” (-5, +7, +3, -8 = -3 threshold not reached).
A competitive element is brought into play with multiple groups of 5 students. Each group has to shout out “fire” or “don’t fire” when their cards are revealed and then if the first responding group is correct (check the math) that group earns 1 point. After several rounds of play (which should go by quickly) the axon hillock role can be switched until everyone in the group has had a chance and the group with the highest overall score wins.
If you want to make it more complex, this game could also be used to illustrate how psychoactive drugs influence neural transmission. This could be done by telling a group they are under the influence of a stimulant or a depressant drug which alters their threshold value. A stimulant could lower the stimulation needed to reach the threshold, as the neuron is now primed to fire more easily (perhaps you would lower the threshold from +5 to only +1). The group should then see that a response of “fire” becomes much more likely than “don’t fire”. In the case of a depressant, however, inhibition would mean that “don’t fire” now occurs more often than “fire” (i.e. say by increasing the threshold from +5 to +9). This is obviously a simplification of the many ways that psychoactive drugs can exert their influence, but it should help students to grasp one way that neural communication can be altered at the level of a single neuron.
My hope is that this exercise can help students to realize that each neuron is responding to inputs from many dendrites simultaneously in order to determine whether or not to fire. Students should see the incredible complexity that goes into the apparently simple firing of a single action potential, without necessarily needing to get into the details of exactly how voltage-gated channels or electrochemical gradients function in order to make this happen. If you have any comments or suggestions for using this activity, please be sure to share them in the comments section below!
