Role Playing A Neuronal Transmission

by Sandra Eidson

Overview

Neuronal transmission of an action potential is one of the highly abstract concepts that role playing can help clarify. The neuronal transmission activity is a class participation activity in which students role play the action potential as it is generated, begins to move down the neuron, and transmits the action potential across a synapse to the next neuron. It is expected that after participation in this activity students will have a better visualization of action potentials, neurotransmitters, and stimulus thresholds.

Biological Concepts

• Structure of a Neuron

• Action Potential

• Stimulus Threshold

• Role of Neurotransmitters

• Myelinated and Non-myelinated Axons

Class Time

Approximately 15-30 minutes of class time will be needed. Class time will vary according to how much time is spent reviewing the parts of the neuron while the students are standing in position and allowing students to role play different variations.

Background

It should be noted that many textbooks incorrectly suggest that the sodium-potassium pump is responsible for the repolarizing phase of the action potential. It is impossible for membrane voltage to be restored to the polarized state by the action of the sodium-potassium pump. Pump proteins act much too slowly for this to be true. This is correctly described by Matthews (1991; p.74), "the repolarizing phase of the action potential is produced by the simultaneous decline in Na+ permeability to its resting level and increase in K+ permeability to a higher than normal level." Therefore, actions of the membrane channel proteins, not pump proteins produce permeability changes. However, the action of the sodium-potassium pump maintains the distribution of sodium ions on the outside and potassium ions on the inside of the membrane. See textbook to examine a graph of an action potential.

Materials

Small squirt gun filled with water, names of parts of a neuron printed on cards

Teacher Preparation and Direction

Class discussion concerning the basic concepts of nerve communication by way of action potentials (including polarized, depolarized and repolarized) and synaptic transmission of an impulse should precede this activity. Before class, instruct the student who will act as the synaptic knob about his/her responsibility. Impress on the students the fleeting nature of the depolarization of the neuron. The depolarized neuron is restored very quickly to the polarized state by the action of the gated ion channels.

Line up students shoulder -to-shoulder. Place the "synaptic knob" at the end of the pre- synaptic neuron (after about half of the students). A small space between the knob and the rest of the line of students will represent the synapse. Review the parts of the neuron by having students in the line wear a card printed with the name of a neuron part. Students representing the dendrites can hold their arms up in different directions to receive the impulse.

Have all students bend and place their hands on their knees to represent the polarized state of the neuron. The student at the beginning of the pre-synaptic neuron will begin a "wave" by raising his or her arms and returning to the bent position. The up position represents the depolarized state of the neuron. Practice, hands on knees (polarized), hands up (depolarized), hands back on knees (repolarized), several times. Then ........The surprise comes when the wave reaches the synaptic knob who squirts the student at the beginning of the post synaptic neuron with a small squirt gun hidden in the palm of his or her hand. This action represents the release of a neurotransmitter into the synapse which acts on the post- synaptic neuron. Students love this activity and remember the concepts.

Extensions/Variations

Repeat line-up with the following variation. To prevent giving students the misconception that neural transmission is always a linear process, have 2-3 students be dendrites and 4-5 students be axons branches. Give each pre-synaptic knob a squirt gun that releases neurotransmitter into the synapse and is picked up by several post-synaptic dendrites.

The neurotransmitter can be played out by squirting varying amounts of water (neurotransmitter). If not enough neurotransmitter is released, an action potential will not be produced. This threshold could be demonstrated by having a post-synaptic student in the hillock of the neuron hold a target. If less than half of the target is wet, the action potential will not reach threshold and the impulse will not continue.

Also have one student completely empty his or her squirt gun by repeated firings to allow the discussion of what happens when there is no more neurotransmitter.

To demonstrate the difference between a myelinated axon and a non-myelinated axon, form two neurons (lines of students) which will race each other. In one line students will pass a ball (or other object) from student to student to illustrate an impulse moving down a non-myelinated axon. In the other line have two or three students pass the ball and then the third student throws it down the line to the sixth or seventh student ( wearing node sign) who throws it quickly to the end of the axon. This illustrates advantage of myelination.

Blockage of the neurotransmitter by drug interaction can be illustrated by placing a piece of plastic wrap over the end of the squirt gun.

Resources

Matthews, G. G. Cellular Physiology of Nerve and Muscle.. Blackwell Scientific Publications, 1991.

About the Author

Sandra Duck Eidson is a biology teacher at West Hall High School in Oakwood, Georgia. Sandra can be contacted at West Hall High School, 5500 McEver Road, Oakwood, Georgia 30566.The phone number at WHHS is 770-967 9826.

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