Neurons are so Impulsive! (Day 1)

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Objective

Students will develop and use a model to explain the role of Schwann cells and myelination in action potential activity.

Big Idea

Schwann cells and myelin sheaths on neurons possess insulative properties which enhance the neuron's capability to generate, sustain and propagate an electrical signal along the axon to communicate with neighboring cells.

Introduction

Lesson Background & Justification:

       An Action Potential is the change in electrical potential associated with the passage of an impulse along the membrane of a muscle cell or nerve cell. This impulse generated, as a result gained momentum, propagates down the axon and finishes with the release of neurotransmitters stored in vesicles at the end of the axon. This ultimately and consequently stimulates the post synaptic cell and repeats the process so that a message may transmitted from short and long distances within the body. In this lesson, students explore the power of positive ions within the cell to understand how electrical impulses are perpetuated and sustained over great distances within the human body.

Lesson Preparations:

 In the effort to prepare for this lesson, I make certain that I have the following items in place: 

a) A class set of 3D Molecular Design: Phospholipid and Membrane Transport Field Test Kit (1 per student group of 4)

b) Student lab books.

c) Class copies of students evaluation worksheets and Action potential simulation guides. 

 Common Core and NGSS Standards:

HS-PS2-6: Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials. 

SP2- Developing and using models.  

Standards Rationale:

      Modeling is the process by which scientists represent ideas about the natural world to each other, and then collaboratively make changes to these representations over time in response to new evidence and understandings. It is intimately connected to other scientific processes (asking questions, communicating information, etc.) and improves students ability to recall scientific jargon through association. In the classroom, it is important that teachers engage students in modeling practices, to set the foundation of success in a lesson or instructional unit. In this lesson modeling is used in concert with other science practices in the classroom to promote students’ reasoning and understanding of core science idea presented (neuron transmission of impulse via action potentials).    

Engage

15 minutes

Section Primer:

         Schwann cells, also called neurilemma cells, are any of the cells in the nervous system that produce the myelin sheath around neuronal axons. These glial cells support the neuron by producing this insulating material (myelin), which is useful to the cell because it promotes the transmission of electrochemical signals to move along nerve axons at high speed. Multiple Sclerosis is a chronic, typically progressive disease involving damage to the myelin sheaths (fat coverings) of nerve cells in the brain and spinal cord, whose symptoms may include numbness, impairment of speech and of muscular coordination, blurred vision, and severe fatigue.

 Section Sequence: 

         In this section of the lesson, my goal is to spark students interest in understanding the significance of myelin sheath coverings in the action potential process. This is accomplished by giving students a snapshot of a condition where the myelin sheath deteriorates (Multiple Sclerosis) first and then follow up with a sequence of activities to aid students fully explaining the sheath's existence. This activity proceeds as follows:

a) State: Recall what you learned or know about multiple sclerosis from the exit ticket in our last lesson. Based on what you know, what part of the neuron is impacted in this condition? How is this part generally formed? (students should have some reference of the myelination process as developed in unit 2 of this course.)

b) Share with the class that we will explore this condition a little more as we continue to understand how neurons function. Let's start with the following clip:

      

c) Post video, revisit initial questions in part a and add, what do you believe is going on under and in between the myelin? Continue to share that the goal is to understand its etiology a little more and that understanding this is the first step in finding a cure. 

Standards Covered:

HS-PS2-6: Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials. 

Explore

40 minutes

Section Sequence:

      In the section of the lesson, my goal is to provide students with an opportunity to explore and utilize models to obtain a visual on a difficult process: Action Potential. The idea is to provide them with physical and colorful manipulative to build association between tough jargon and familiar items.I proceed as follows:

a)  Slide 1: Remind students that the goal is to understand what happens in the node of Ranvier and the sheath between them(iterate their locations by pointing them out on the screen).  Provide every student pair with a membrane model kit and a copy of the action potential simulation instructions and student worksheet. Instruct students to read and follow the simulation directions and to address the questions on the corresponding student worksheet (this serves as the students notes for the process) as they progress. 

Note: Give Students adequate time to work through this process as it can be difficult to grasp. Circulate and provide unsolicited support to each group to make certain that they are clear on direction specifics and are actually grasping the goal of the activity. Ask if they have figured out anything about why some patients suffer certain symptoms of MS? etc. 

Slide 2 can be used to clarify how relative negative and positive charges can be created in and outside of the cell with only positively charge ions. This can be done prior to student pursuit of the activity or demonstrated when they have this specific question during the activity. 

 Standards Covered:

SP2- Developing and using models.  

Explain

40 minutes

Section Sequence:

      In the section of the lesson, my goal is to provide students with an opportunity to digest the process of starting and propagating an action potential to align any misconceptions acquired during the simulation in the exploration section. I proceed as follows:

a) Ask: How many of us feel comfortable with explaining an action potential? Survey class and use a simple raise of hand method to quantify student numbers. If student numbers are high, ask: How many of us could use some clarification on the process? Survey class and quantify by hand count. Proceed with the following video if students numbers (30% or more of the class) require a more fluid explanation of action potential generation and conduction. Pause to explain areas that you observed students struggling with during the simulation activity.  

                     

b) Post video, reask "How many are more comfortable with the process now?" Discuss.

c) Share with students that we are now going to attempt propagate an action potential in real time. Instruct students to do the following:

1) Construct their models in the shape of a neuron. This time use small cut outs of construction paper to create sheath coverings. Tell students that all active transport must occur between these nodes of Ranvier. 

2) Situate equal numbers of neurons (all facing in the same direction) on each side of the room.

3) Take time to improve your speed on simulation the propagating an action potential before the big potential race. Compare this to the process of Neuroplasticity. That is, the speed of the impulse occurs quicker with greater usage of practice. 

4) Announce that each side will race one another to get their message from the back to the front of the room first. (Remind students of the node rule). Allow students to race and time them.

5) Ask students how they could utilize the neuron model to simulate neuron impulse activity in those with MS. Allow students to develop a representation of neurons impacted by MS using some of the models and instruct them to repeat the race with some missing or destructed sheaths. Set the standard of electrochemical movement through an unmyelinated area of the axon by telling students that it will take 15 seconds to move through these destroyed areas. Record, compare/contrast speed times of a healthy pathway to one affected by MS.

Wrapping up!

6) Instruct students to produce an illustrative representation of a healthy person's action potential activity compared/contrasted to those with MS in their lab books.  Encourage students to use acquired lingo to annotate their illustrations.  

Standards Covered:

HS-PS2-6: Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials. 

SP2- Developing and using models.