Identify and distinguish between the ions and proteins important in action potentials
Distinguish between membrane potentials and action potentials
Describe the process of message transmission down the axon of a neuron
Introduction: In the last activity, you learned about the different cells of the nervous system: neurons and glial cells. In this activity, we will be learning about how messages are sent in neurons and how one specific type of glial cell can help it happen!
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Warm-Up 1
Find a meme to describe how you're feeling today. Place it in the 'show your work' box below.
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Warm-Up 2
a. What is an ion?
b. Think back to the muscle unit... which ions are important in muscle contraction?
Part 1: Neuron Structure and Membrane Potential POGIL
Cells are specialized for different functions in multicellular organisms. In animals, one unique kind of cell helps organisms survive by collecting information and sending messages throughout the body. The shapes and features of neurons, which are the primary cells in the nervous system, enable animals to experience all of the five senses; find food, mates, and shelter; and to survive in their diverse environments.
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Model 1 is an illustration of two neurons.
Click on the 'show your work' box below, then label both neurons in Model 1 with the following terms:
cell body
nucleus
dendrites
axon
synapse
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Which structure on the neuron in Model 1 would receive a signal from either a sensory cell (taste bud, touch receptor, retinal cell, etc.) or from another neuron?
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What is the arrow in Model 1 displaying?
Model 2 (below) is a very 'zoomed in' diagram of the cell membrane of a neuron at rest (the neuron is not sending an electrical signal).
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Which part of the neuron is displayed in Model 2? (hint: look for the "area of detail")
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Identify each of the following symbols in Model 2
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Phospholipid
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Potassium ions (K+)
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Sodium ions (Na+)
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Ion channel
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Click on the 'Show your work' box below. On Model 2, color the potassium ions (K+) green and the sodium ions (Na+) red.
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Which side of the membrane has more sodium ions (Na+) when the neuron is at rest?
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If a channel were to open, which direction would sodium ions (Na+) flow?
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Which side of the membrane has more potassium ions (K+) when the neuron is at rest?
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If a channel were to open, which direction would potassium ions (K+) flow?
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The two different types of channels in Model 2, outlined in red and blue in the model below, illustrate active transport and passive transport.
Which channel, the channel outlined in red or the channel outlined in blue, do you think illustrates active transport? Explain your reasoning. (Hint: If you're stuck, think about what the terms active and passive mean)
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Look in the model for the sodium/potassium pump. Which ions move in and out of the cell with the help of the sodium/potassium pump?
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potassium
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sodium
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What is the resting membrane potential of a neuron?
Read This!
When a neuron is "at rest," it is constantly pumping sodium ions out and potassium ions in to maintain a potential across the membrane of about -70 millivolts (mV). The outside of the neuron has a slightly positive charge, the inside a slightly negative charge. The sodium/potassium pump process must be continuous as the ions will "leak" back in or out in the direction of the concentration gradient. The resulting membrane potential is caused ny a combination of factors including the relative number of positive and negative ions on each side of the membranea and the properties of the ion channels themselves. In this state, the neuron is always ready to quickly respond to a stimulus.
When a neuron is stimulated, there is a change in the membrane potential. Examine model 3 below, in which an electrical message is being sent down a neuron.
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Which side of the membrane (as you see it) in model 3 is responding to a simulus?
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The protein channel illustrated in Model 3 is a ligand-gated channel. Watch the video below about ligand gated channels:
What must occur for the "gate" to open and allow movement of ions across the membrane?
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Use the 'key in lock' analogy from the simulation to match the structures:
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key
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lock
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what goes through the "door"
Continue to consider model 3 as you answer questions 19-23
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What type of ions are moving through the ligand-gated protein channel when it opens?
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The ions going through the ligand gated channel are moving _________ the original concentration gradient.
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Is the transport of ions across the membrane active transport or passive transport? Justify your reasoning.
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When the gated channel is open and ions flood through, what happens to the concentration of that ion species inside of the cell.....
Decreases
Increases
Stays the same
... in the immediate vicinity of the protein channel?
... in the area further away from the protein channel?
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Examine the voltage readings across the membrane in Model 3:
How does the flood of ions through the gated channel affect the membrane potential....
The membrane potential gets more negative
The membrane potential gets more positive
The membrane potential does not change
... in the immediate vicinity of the protein channel?
... in the area further away from the protein channel?
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Extreme athletes use sports drinks not only to hydrate but also to replenish the electrolytes (ions) in their body that are lost through sweat. Propose some reasons why this would be necessary to keep an athlete healthy and in top condition.
Part 2: Action Potential Simulation
The simulation below represents a cross-section of an axon in a nerve. The yellow represents the cell membrane of the axon. The myelin is not shown in this model.
When you click 'stimulate neuron', you'll notice a purple and yellow thing moving down the length of the axon: this represents the action potential. What you'll be observing in this activity is what happens when the action potential reaches this cross section of axon. You are not observing the entire nerve cell - just a small fraction of its membrane. The changes you observe here are what happen down the entire length of the neuron.
Spend 3-4 minutes playing with the simulation below. Think to yourself:
what things do you recognize from the POGIL activity?
what things do you NOT recognize from the POGIL actvity?
what things can you "change" on the simulation?
Use the simulation to answer questions 25-32. Note: you're going to need to zoom in, change speeds, and pause the simulation to really understand what is happening as you work through these questions! You should also click on all of the 'boxes' to the right.
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Consider a neuron at rest. Match the following:
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The membrane channels that are open
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The membrane channels that are closed
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Are more channels open or closed when the axon is at rest?
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Which side of the neuron is negatively charged when the neuron is at rest?
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The simulation only shows positively charged ions. How can one side of the membrane have a net negative charge in this scenario? (Hint: what must be present but is not shown in the image?)
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On the axes provided, sketch the graph that is generated when you click 'stimulate neuron'. Include ALL necessary titles, labels, and units. (note: this does not ned to be perfect, so please don't bother writing every number or filling in grid lines.)
If you would like to have the simulation open in another window on your computer, click here.
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What is the membrane potential (in mV)....
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-70 mV
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+40 mV
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-75 mV
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Which side of the membrane has a net negative charge....
outside
inside
at rest
at the peak of the action potential
immediately after the action potential
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32.
Consider the movement of sodium and potassium ions at...
Sodium ions enter the cell
Potassium ions leave the cell
Sodium ions leave the cell
Potassium ions enter the cell
the beginning of the action potential
the peak of the action potential
immediately after the action potential
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Watch the 2 minute neuroscience activity about the action potential:
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Depolarization
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Threshold
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Repolarization
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Hyperpolarization
Part 3: The Role of Schwann Cells
Watch the video below about the role of Schwann cells in the action potential:
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What is the role of schwann cells in the propogation of an action potential in a neuron?
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Multiple sclerosis (MS) is the most common disease of the human body that involves myelin. In a patient with MS, the immune system attacks either the myelin sheath surrounding the axon of PNS neurons OR the Schwann cells that produce and maintain the myelin.
Without googling (please!) - think:
What symptoms might a person with MS experience? Why?
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As always, we will start our next class discussing questions you have about this lesson.
What are two specific questions you have about action potentials? Please do not write 'IDK' or 'nothing'.
Optional Resources:
If you would like to look through the section from our textbook all about action potentials, click here.
If you want to check out the crash course on action potentials, enjoy:
