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Biology: Motor Control: Muscle Microstructure


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About this Lesson

  • Type: Video Tutorial
  • Length: 10:18
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 111 MB
  • Posted: 07/01/2009

This lesson is part of the following series:

Biology Course (390 lessons, $198.00)
Biology: Animal Systems and Homeostasis (63 lessons, $84.15)
Biology: Motor Mechanisms (4 lessons, $5.94)

Taught by Professor George Wolfe, this lesson was selected from a broader, comprehensive course, Biology. This course and others are available from Thinkwell, Inc. The full course can be found at The full course covers evolution, ecology, inorganic and organic chemistry, cell biology, respiration, molecular genetics, photosynthesis, biotechnology, cell reproduction, Mendelian genetics and mutation, population genetics and mutation, animal systems and homeostasis, evolution of life on earth, and plant systems and homeostasis.

George Wolfe brings 30+ years of teaching and curriculum writing experience to Thinkwell Biology. His teaching career started in Zaire, Africa where he taught Biology, Chemistry, Political Economics, and Physical Education in the Peace Corps. Since then, he's taught in the Western NY region, spending the last 20 years in the Rochester City School District where he is the Director of the Loudoun Academy of Science. Besides his teaching career, Mr. Wolfe has also been an Emmy-winning television host, fielding live questions for the PBS/WXXI production of Homework Hotline as well as writing and performing in "Football Physics" segments for the Buffalo Bills and the Discover Channel. His contributions to education have been extensive, serving on multiple advisory boards including the Cornell Institute of Physics Teachers, the Cornell Institute of Biology Teachers and the Harvard-Smithsonian Center for Astrophysics SportSmarts curriculum project. He has authored several publications including "The Nasonia Project", a lab series built around the genetics and behaviors of a parasitic wasp. He has received numerous awards throughout his teaching career including the NSTA Presidential Excellence Award, The National Association of Biology Teachers Outstanding Biology Teacher Award for New York State, The Shell Award for Outstanding Science Educator, and was recently inducted in the National Teaching Hall of Fame.

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How do nerves talk to muscles? Here comes a scientific demonstration. Ready? I'm going to send a message to my arm. And I'm going to make this muscle contract. Now I could that even without doing this. Watch, ready? Now, what's going on here that I did that? Muscles work in opposable pairs so when I contract my biceps, to now make my arm move down, I have to do two things. I have to relax my biceps and then contract my triceps. So there's a couple of lessons here.
One of the things I want you to understand is that nerves talk to muscles. There's something called a neuromuscular junction. Now we're going to talk about that and the ionic events that occur there, at another time, because first I have to make you understand what muscles are. And then the second thing I want you to understand is that muscle fibers, muscles can only do two things. Contract or not contract. And we call that not contracting, relaxing. But really, that's all that it is, that's all muscles do. Get rid of the concept, if you had it, that now I'm contracting my biceps and now I'm pushing my biceps back. You can't do it. You can only relax that. You have to contract this. Opposable pairs.
Well, that's pretty cool. How do muscles work? What is a muscle? Well, if you've ever eaten meat and a lot of steaks, it's hard to see this in, because we cut our steaks in cross section rather than in longitudinal section, but the next time you're butchering an animal, I want you to look at its muscle. Or the next time you eat like a chicken leg. Because you get the whole muscle on the chicken leg. You rarely eat like cow legs. But if you eat a chicken leg, take a look at the muscle and you'll notice that there's long lines in the muscle and if you look very closely, there's actually lines in the chicken muscle. The reason we have those long lines is we have to take a look at the way muscles are built.
Let's take a look at a muscle. Here's a muscle. We'll make it an arm muscle rather than a leg muscle. So there's an arm muscle. And you could see that they are built to work with this longitudinal way. If you take a look at a muscle and you start to dissect it apart, you see that it's consisting of long fibers, which we call muscle fibers. Which is a good thing to call them. However, muscle fibers are really muscle cells. These are actually cells and they are multinucleated cells. That's an embryological thing, but what ends up happening embryologically is your muscles end up fusing and you get multinuclei in there. Then if you take a look at one of these cells - let's take a look at one muscle cell, one single fiber or cell. We see that it is like a cable. Inside of that cell, most of the cytoplasm is taken up with these long cables. That's the whole idea of the multinucleation. Really, I should say it another way. You have few cells which provide multinuclei but the point is that it is so you have one long continuous cable the length of that whole muscle cell, which will go the length of my muscle, you see. So, we have these long cables in there. And these cables, which are sometimes referred to as myofibrils - the word "myo" often refers to muscles - are actually microfilaments. That's right. Things you know about. Filaments of actin and myosin. And it's the actin and myosin, which is going to provide us the magic of the way a muscle works.
Actin and myosin filaments. Let's take a look at how they are arranged in a muscle cell. If you take a look at, say, a micrograph of a muscle, we see that it seems to involve these, like, repeating units. Let me go back to this diagram here. You notice that there is what looks like some kind of zonation to the idea of a muscle fiber. There's a zone of some kind in there. I remember my anatomy and physiology days - all of these sections have names. There's different bands. But what I really want to concentrate on here, is what's going on here? What are we seeing? I'll give you the artist's rendition and then I'll draw for you what's going on here. What you can see is there is a correspondence that you can make out between this diagram and this diagram. You see that there is a dark area in the center and then two light areas here and here. And then, it repeats. So there's my dark area again. What's going on here is this is the way the actin and myosin tubules or filaments are arranged. The actin and myosin filaments - what do they do? Let's look at it in a diagrammatic form first. In a diagrammatic form, it will look something like this. The myosin filaments are very thick and they have these portions, the structure of the protein is such, or the filament is such that they have these heads sticking off of them. I'm going to refer to them as the myosin heads. In a relaxed muscle, sitting above the myosin filaments and below the myosin filaments, are thin fibers, called actin. And they are not attached, in the relaxed state. That's what it looks like in longitudinal section. But what this really forms is, if you were to look at a muscle in cross-section, you would see a very different story. You would see an entire network of these fibers and that, including this diagram here, is going to give you an idea of how this all works together. What you would see, just to get you started, would be something like this. I'm in cross-section now. What I'm going to see is I'm going to see my actin and it's going to look something like this. You're going to have a myosin filament attached to an actin. And what you're going to form is this kind of network of actin-myosin filaments.
So, literally, when you take a look, what we get is this whole idea of this meshwork so that when these things are connected to each other, they can somehow work as a unit. And how are they going to work as a unit? These are going to work as a unit by what we call the sliding filament theory. And this is when it's going to get interesting. If it's not interesting yet. Which, for me, I'm like really there. But, the point is that eventually what's going to happen is you're going to be able to view a muscle here as a network of fibers and this network of fibers are going to be constantly interacting so that when this muscle - imagine all these pink things sliding up out of the paper and imagine that this is a muscle cell. Well think about this. If these small filaments slide up out of the paper and these remain constant, and they're going to be pulling on each other, that muscle fiber is going to tighten. And if we look at it from the longitudinal section like this, you can see that that would work, too. If these microfilaments of actin move that way, and these microfilaments of actin move that way, and these move that way, and these move that way, what are you going to do? You're going to shorten up your muscle. And that is called the sliding filament theory of muscle action. The fact that these filaments slide on each other. How do they do that? It's a long story and we'll talk about it later.
Animal Systems and Homeostasis
Motor Mechanisms
Motor Control: Muscle Microstructure Page [1 of 2]

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