Title: Neurons and Action Potentials
Overview:
In this lesson, students will learn about ion flow and membrane potential during an action potential in a neuron. Channel position, graphing and naming of the different stages of action potentials will also be discussed. Applications of this information are introduced using neural data, sound clips and an online program showing the concept of the refractory period. Following the activity, students will be given a worksheet asking them to describe what they did during the activity and apply what they learned to more abstract questions.
Objectives:
The students will learn:
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Neurons are specialized cells composed of various parts with specific names and functions
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Neurons transmit information using action potentials
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Action potentials are generated by the flow of ions across the cellular membrane
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Scientists can record action potentials and use the information to associate the corresponding area of the brain to distinct behaviors
Arizona State Standards:
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Strand 1: Inquiry Process o Concept 1: Observations, Questions, and Hypotheses (Formulate predictions, questions, or hypotheses based on observations. Evaluate appropriate resources.)

PO 1. Evaluate scientific information for relevance to a given problem.
 PO 2. Develop questions from observations that transition into testable hypotheses.
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PO 3. Formulate a testable hypothesis.
 PO 4. Predict the outcome of an investigation based on prior evidence, probability, and/or modeling (not guessing or inferring). o Concept 2: Scientific Testing (Investigating and Modeling) (Design and conduct controlled investigations.)
 PO 5. Record observations, notes, sketches, questions, and ideas using tools such as journals, charts, graphs, and computers o Concept 3: Analysis, Conclusions, and Refinements (Evaluate experimental design, analyze data to explain results and propose further investigations, design models)
 PO 1. Interpret data that show a variety of possible relationships between variables, including:
 positive relationship
 negative relationship
 no relationship

 PO 2. Evaluate whether investigational data support or do not support the proposed hypothesis.
o Concept 4: Communication (Communicate results of investigations)

PO 2. Produce graphs that communicate data.
 PO 3. Communicate results clearly and logically.
 PO 4. Support conclusions with logical scientific arguments.
National Standards:
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Science as Inquiry o Abilities necessary to do scientific inquiry o Understandings about scientific inquiry
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Life Science o The cell
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Science and Technology o Abilities of technological design o Understandings about science and technology

Science in Personal and Social Perspectives o Personal and community health
Materials and Resources:
Action Potential Activity:
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For Each Group:
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Enlarged and simplified drawing of a neuron, showing the soma, dendrites, axon, ion channels and terminal branches
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14 brads
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5 red construction paper rectangles, the length of the openings left for ion channels
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6 yellow construction paper rectangles, the length of the openings left for ion channels
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3 blue construction paper rectangles, the length of the openings left for ion channels o Note: The construction paper rectangles should be attached to the drawing of the neuron, in no particular order, with the brads. To save time, this should be done prior to the class period.
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165 dried black-eyed peas
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130 dried lima beans
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155 dried pinto beans
 Large construction paper circles labeled with a “-” (these represent proteins and other large ions found in a cell and should be larger than the openings used to represent ion channels)


Stopwatch
Supplemental Information:

Online simulation of an action potential, generated using the Hodgkin-Huxley equation. http://afodor.net/HHModel.htm

Youtube video demonstrating a mapping technique in the visual cortex of a cat. The scientists are recording from a neuron that fires in response to visual stimuli in specific areas of the cat’s visual field. The discharge of the neuron is actually the increase in static noise heard during the video. http://www.youtube.com/watch?v=KE952yueVLA
Assessment:
Group discussion
Action Potential Graphing
Post Activity Worksheet
Lesson Plan:
Action Potential Activity (25 minutes)
Decide ahead of time how many groups you will divide students into. Groups should consist of about 5-7 students. Set up the drawings and other materials where you would like each group to work, leaving the beans and other items in pile. As the students walk into the classroom, divide them into the predetermined number of groups and have them go to the corresponding table.
Verbally walk through an action potential with the students. Make sure to discuss the specific ions involved, where/how they move before and during an action potential, the discrete parts of the action potential, and the corresponding membrane voltages.
•
•
Next, provide the students with the following information:
•
Sodium channels open for approximately one millisecond
Potassium channels open for between one and three milliseconds
Proteins are too big to fit through these channels

•
Particle
Concentration
Inside Outside
Sodium 15mM 150mM
Potassium 150mM 5mM
Chloride 10mM 120mM
Also tell them that there is a correct way to assign each of the beans to the particular ion they are representing
Tell the students that their task is to model the flow of ions leading up to and during the firing of an action potential. Have them fill out the first few questions on the worksheet while they are doing the activity.
As you walk around the classroom, ask the students what each part of the drawing is and what each material represents and why. If they open a channel, ask them why they had it open for that exact period of time. Make sure that they use the stopwatch and recognize that a millisecond is too short to time and that they must use multiples for this representation. Also, ask them more abstract questions, such as “What if I this neuron was exposed to a drug that had the ability to shut down all of the sodium channels, how would that affect the action potential?” or “Why do the sodium ions flow into the cell and not out of it during depolarization?”
Simulation (10 minutes)
When each group has successfully demonstrated the action potential, use the Hodgkin-Huxley simulation to show the effects of losing part or all of the ion channels. The simulation can also be used to show that a stimulation applied during absolute refractory will not generate an action potential.
Real Life Applications (10 minutes)
Next, the Youtube video is a great demonstration of how scientists use neuron discharges in real life. The video shows a series of lights in different shapes, locations and orientations. You are essentially seeing what the subject (a cat) was seeing during the experiment. The researchers have electrodes located in the cat’s visual cortex. As the light moves, the discharge of a neuron can be heard and sounds like an increase in the amount of static. The scientists can deduce that the neuron they are recording from at that time is sensitive to light in that area of the cat’s visual field. This sort of work is routinely done in many areas of the brain to “map” and “decode” what each part is specifically “tuned” for.
Review/Reflection (10-15 minutes)
Verbally review the steps of an action potential. It was useful to relate the words to other, more common concepts. A great example refers to depolarization and hyperpolarization. First make

sure that they associate the words to the charge of the cell. Guide them to come up with the term hyperpolarization by talking about an elbow and ask them what it is called when someone extends their elbow too far in the wrong direction. When they say “hyperextend”, ask them what they think people call the period when the charge is over shot by the neuron. Next, draw a 2D axis on the board and ask for volunteers. Have the students draw an action potential (membrane potential vs. time). Have each student volunteer draw one piece (i.e. depolarization, repolarization, etc.). It is also beneficial to have them label the positions of the channels, axes and different parts of the graph.