Biology: Muscle Structure and Action

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Alright I want to talk to you a little bit about muscles and I want to ask you a question. What do you think of when I say the word muscle? And now you know if I could read all of your minds it would illustrate the dilemma we have in anatomy when we start talking about muscles because you probably all, most of you probably thought of like muscle, you know making what we used to say making them. We probably still do say making a muscle and for those of you who care that's called the biceps. But you want to know something? We have some dilemmas and the dilemma is how do we classify muscles. For example we have talked in the past about the microscopic structure of muscles and we characterize muscles not so much by where they are or what they do but how they look under a microscope because there are three very clear differences between different types of muscles. I could take one type of muscle and I could slice it and look at it under a microscope and you will see the striations in it, these cross hatches if you will. So we say aha we are going to call that striated muscle. But then we look at other muscles and we see that wow those striations lack and so we will call that smooth muscle. And then we look at a third muscle like the muscle of your heart and this one in particular seems to almost be a blending of those two. And so we call that heart muscle, cardiac muscle because it's just bizarre into itself. Well that's one way to do it. But then there is another way we can classify muscles and we can classify by the way we say they are innervated or in other words how they are controlled. So for example we could say some muscles are voluntary muscles. So for example, when I say raise your arm, you did it you see. But when I say make your heart beat faster you can't do that. Why? Because that's involuntary, you see. So and some muscles are actually sometimes voluntary sometimes involuntary but there is a classification. We can say voluntary or involuntary and thirdly we can say well we can go by location. For example we could say that muscles are attached to a skeleton and if they are attached to a skeleton we will call them skeletal muscles. And if they are not attached to a skeleton and they are the muscles of your gut for example your diaphragm we will call them the visceral muscles and again we will put the heart as a cardiac muscle all into itself. So you see typically we have in anatomy, we have different ways of looking at things and I want to talk right now about those muscles that you probably thought of when we started out and I am going to generically refer to those as the skeletal muscles, those muscles that are attached to our skeleton. So we got location that are voluntary although can sometimes be involuntary and I put that are voluntary and that are striated, okay. And so we are going to generically call them or anatomically call them the skeletal muscles, alright. So let's talk about the anatomy of these skeletal muscles and let's talk a little bit about the, let's extend what we know from a microscopic level to the macroscopic level if you will. Now thinking back to the way muscles organize we know that muscle cells are elongated cells. In fact if I could magnify this picture right here of a generic muscle we would see that we have these long fibers. But if I went deeper I would see elongated muscle cells and then I would see that these elongated muscle cells are built into kind of like bundles called fascicles and these fascicles upon fascicles build up and end up with these muscle fibers if you will and that gives me a muscle. So in this particular muscle fiber this elongated or this particular muscle, this elongated muscle we have very, very long muscle fibers. Now the other thing about this muscle is there is a structure along the outside of every muscle and this particular structure is called the epimysium. Now the epimysium is a tough membrane, a bag around a muscle and this is kind of cool because it extends. So it encloses the muscle and then it comes down to the end and it kind of pulls in and it makes a very, very strong connective tissue and for this, this is how these skeletal muscles are attached to bones alright. And so these very strong connective tissue points otherwise known as tendons will connect the muscle to a bone thus the word skeletal muscle. So now there is one other thing about these tendons which is kind of cool. Some of them are quite stretched out. So for example in this long flat muscle right you can see that there would be a tendon here but to call this a tendon an elongation of the epimysium is really not accurate. It's kind of a broad extension of the epimysium and we have another word for that and that's called aponeurosis. But it's just a long flat tendon but don't tell anybody I told you that. So that's kind of what the structure of a muscle is. Alright so far so good. Let's talk about where muscles are found and what they do. Well skeletal muscles are attached to a bone okay and where they are attached to a bone they are generally going to span a joint. Well why is that? Well remember the function of a skeletal muscle. A skeletal muscle's function generally is to move. So in most cases at least the muscles we are talking about without getting into the in-depth anatomical relationships of every muscle of your body we can generically say that the muscles we want to look at are going to span a joint and we will talk more about joints in a little bit. So they are going to be attached to bones and they are going to span a joint and they are going to be placed in regions where they attach on one bone and attach on another bone. Well okay why? Well if you are spanning a joint, I happen to have a joint right here, okay alright. If you are spanning a joint you are going to literally cross from this bone, which as you know is my humerus. So I am attached to my humerus here and I am going to cross this joint right here and I am going to be able to move this thing, alright like so. So one muscle is going to have what's called the origin and the origin is the anchor. So my biceps is anchored up into my shoulder and it's going to extend down to my lower arm and its going and that's where what we call the insertion is. So every muscle, every skeletal muscle is going to have an origin and anchor and an insertion, the bone that moves okay. So when we have these skeletal muscles that are actually going to move a limb we are going to have the spanning of a joint and we are going to have an origin and insertion and every muscle that's attached is going to have an origin and insertion. Now sometimes muscles are going to contract and you can actually define and there is not a clear anchor and moving point. So just one little side thought to that, another way we can define the origin is that the origin is where the broadest attachment is because we have got to have one called an origin and one called the insertion. So if there is not an obvious anchor we will say it has the broadest attachment and the insertion has the smaller attachment. Okay so let's talk about the different types of muscle movements. So this is kind of cool. So far muscles are easy. They are attached to skeletons, at least the muscles we are looking at. They kind of move things. The cool thing about muscles is this. They work in opposable pairs, okay. Now what does that mean? Generally speaking when you, a lot of people think watch this right, here is what they think. They think when I pull my arm up okay that I am actually contracting my bicep and you are right. But here is what, this is wrong. Here is a misconception people think that when I move my arm down I am extending my bicep. Wrong. See my biceps can only contract. In fact there is no muscle in your body that can contract and then expand. It's not the way muscles work. Go over your muscle physiology you will see that. You have got the shortening of those fibers inside of a muscle, another story about great stuff. So then how do I do this? Is that gravity? Do I just kind of like let it fall when I raise my shoulder? Is there a way to pull my arm down or is it just gravity and gravity accelerating it. And the answer is no. They are working in opposable pairs. One muscle opposes the other muscle. So I have biceps to pull my arm this way and triceps to pull my arm that way across this elbow joint. Again we will talk more about joints later. So let's talk about these different kinds of movements okay and by the way we call one the agonist and one the antagonist, agonistic movement antagonistic movement, opposable, see opposable pairs. Let's talk about the basic types of muscle movement. First of all we have a movement called flexing. You know that one. You flex your bicep right or did you know you were using an anatomical term when you said I flexed to my bicep today? Well you were because flexing has a definition. It's called flexion and it's a bending movement that actually decreases the angle of a joint. So in other words it's bringing the bones closer to each other whereas extension is increasing the angle of a joint or bringing the bones further away. So flexing extending, cool. Here is another movement and these are the big two. Flexing and extending is one opposable pair of movements. The other one is abduction and adduction. If you are not careful about the way you pronounce those you will confuse your friends and relatives. So be careful. Its abduction and adduction. What's abduction? Abduction is the movement of the limb away from the midline. So here is the midline of my body. I am moving my limb away from the central line. I could do with my leg too but you won't see my leg and I am not so sure I could stand up but we will go with arms right now. See so I am moving it away from my body or away from the midline. Well I am going to now adduct. I know you like to say well why don't you just call it raise and lower? Deal with it. So I am going to abduct and I am going to adduct, abduct, adduct. Double abduction, double adduction. And sometimes you can combine flexion and extension and abduction and adduction. How? Watch this. So see what I am doing. It's kind of, I have got, I mean I have a lot of muscles doing this cone like movement. Look at that. That's called circumduction. Circumduction I am flexing I am extending I am abducting I am adducting I am doing the whole thing and all these different muscles being controlled by my brain, remember they are voluntary, are just doing this very smooth movement in microseconds. I could do that all day. That's really that's amazing, the nervous control. Okay so there is muscles. Where they are, what they do, how they work and the terminology removed for them.
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Muscle Structure and Action Page [1 of 2]