The Correct Choice
In my current anatomy and physiology class, we've gotten to one of my favorite chapters: nerve. This chapter is one of the most difficult to understand because it's the first chapter I require the students to really synthesize the information and apply what they learn. We're not just memorizing anatomical structures...you need to know the physiological mechanisms and everything that can go with them.
Having said that, I ease them into the unit. We cover the anatomy of a neuron (it's like a representative cell, which we covered in Chapter 3), including all of its special parts. You see, not all cells have dendrites, axons, axon endings, and myelin sheaths. I've unearthed a very simple picture of a neuron and shared it below (courtesy http://the-works.net/tag/the-neuron-diagram).
We spend a long time trying to understand what happens at the plasma membrane because changes in the ion distribution across that membrane are the basis for how the nerve communicates. We talk some math (don't leave me, FRN, this will be okay), but not much. The bottom line is this: the plasma membrane has ion channels in it (see the purple protein above). If you open those ion channels, ions can flow through (the channels are usually specific for one particular ion, but you don't need that information here), and when those ions flow, you are creating a change in the system. In effect, you're making change to the concentration of ions inside the cell, and that change inside the cell will make the neuron send a signal.
Okay, I realize to some of you that what I just said might not make sense. But believe me, with the PowerPoint presentations and the 50 times I repeat important points, I would at least think that the students in my class would walk away from the lectures knowing a few things. Namely, that the plasma membrane has different concentrations of ions on either side of it, and if we alter that distribution, we can, in effect, send a message. Furthermore, I would hope that they'd realize the plasma membrane exists on all cells, including the neuron. We did, after all, learn about all the intimate details of said structure.
But you all know where this is going, don't you? I gave an exam the other day, one I thought was more than fair. I'd reworked my questions so that I had a large percentage of easy questions, hoping that the easy points would bolster the students' confidence. One of the exam questions asked the following:
Yes, we discussed that the axon is the portion of the neuron that conducts the signal, and that the signal can be called a nerve impulse. We also talked about the fact that no neuron acts alone! Our brain is made up of 100 billion neurons and so one single neuron must carry on at least several conversations at the same time. Which gets us to the last choice, d. Does the neuron lack a plasma membrane? Hadn't we just discussed (over and over again) the idea that neurons possess many characteristics of all cells? Hadn't we belabored the point that ions pass through channels in that membrane? Why yes, yes, we did. So the neuron must HAVE a plasma membrane and therefore the correct choice must be d. Right?
And you wonder why I worry about our future. These kids these days. My bet is most of them didn't understand what the term "lack" meant, and if that is true, my friends, the world is worse off than I thought.
Having said that, I ease them into the unit. We cover the anatomy of a neuron (it's like a representative cell, which we covered in Chapter 3), including all of its special parts. You see, not all cells have dendrites, axons, axon endings, and myelin sheaths. I've unearthed a very simple picture of a neuron and shared it below (courtesy http://the-works.net/tag/the-neuron-diagram).
The one detail that is not visible on the picture above is that the entire structure is surrounded by a plasma membrane. All cells have plasma membranes. They are phospholipid bilayers that allow some substances in and keep others out, a boundary between outside and inside, if you will. The plasma membrane is very important in nerve, and so, we discuss the topic at length. (In case you're curious, a zoomed in picture of a generic plasma membrane is shown below).
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| Courtesy of http://biology.tutorvista.com/animal-and-plant-cells/plasma-membrane.html |
Okay, I realize to some of you that what I just said might not make sense. But believe me, with the PowerPoint presentations and the 50 times I repeat important points, I would at least think that the students in my class would walk away from the lectures knowing a few things. Namely, that the plasma membrane has different concentrations of ions on either side of it, and if we alter that distribution, we can, in effect, send a message. Furthermore, I would hope that they'd realize the plasma membrane exists on all cells, including the neuron. We did, after all, learn about all the intimate details of said structure.
But you all know where this is going, don't you? I gave an exam the other day, one I thought was more than fair. I'd reworked my questions so that I had a large percentage of easy questions, hoping that the easy points would bolster the students' confidence. One of the exam questions asked the following:
- Which of the following is not true with respect to axons?
- It is the conducting region of the neuron.
- It generates nerve impulses.
- It can carry on many conversations with different neurons at the same time.
- It lacks a plasma membrane.
Yes, we discussed that the axon is the portion of the neuron that conducts the signal, and that the signal can be called a nerve impulse. We also talked about the fact that no neuron acts alone! Our brain is made up of 100 billion neurons and so one single neuron must carry on at least several conversations at the same time. Which gets us to the last choice, d. Does the neuron lack a plasma membrane? Hadn't we just discussed (over and over again) the idea that neurons possess many characteristics of all cells? Hadn't we belabored the point that ions pass through channels in that membrane? Why yes, yes, we did. So the neuron must HAVE a plasma membrane and therefore the correct choice must be d. Right?
And you wonder why I worry about our future. These kids these days. My bet is most of them didn't understand what the term "lack" meant, and if that is true, my friends, the world is worse off than I thought.
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