Okay, so in this video we're gonna be talking about acting and skeletal muscle contractions. So skeletal muscle contractions depend on interactions between two proteins acting. And my since we've talked about acting. So what is my sin? So my sin are die MERS. So they have two heads which have a T. P. Ace capabilities and a tail that is uh coiled coil. So it just pretty much means it's wrapped around each other that extend outward from the heads. And so they also form filaments. They form myosin filaments and they are clusters of this miocene to and so they kind of look like a double headed arrow. Some people say, I think they look like other things. You can kind of figure out what they look for by yourself. Um But anyways that's what people say. And then pretty much there are two mice and filaments that bind to each acting filament. And each one of these medicines buying an opposite orientations and that allows for them to move the acting in opposite directions. And this will make more sense when I show you the picture. Um But you'll have to bear with me on some of these pictures. But right now this is what my son looks like. So you have your two heads. These are these have a T. P. S. Capabilities and you have this long coiled coil tell. So this is gonna be a mice and filaments. So there's lots of them here you can see um and there are bound in opposite directions to the acting. And so um skeletal muscle is made up of these active and missin. Um and their distinct organization, what you actually need to know what all of these features are called. And this organization and these features allow for muscles to contract. So um bundles of acting and mason are called fibrin. Microfiber als. Um And inside the the liberals. Oh goodness! I can't say that. And then you have circle manners inside of them. And the star chrome mirrors are the tiny units that actually contract. And there's many of them in these vibe roles. So inside a circle mirror, there's a lot of different structures you need to know about. There's an A band. And this is composed of my sin. You may also see this as a thick filament. It's the same exact thing. Then you have the H. Zone which is in the a band. And this is a lighter region. And my sin is not overlapping with acting. So here you have some medicine with overlapping with acting. In here you don't. And then you have the in line which is the disc in the middle. I think that might be the easiest one to remember because it's the in line in the middle. Um But then you also have the eye band to have the A. And I band I band is called the light band. And it's composed of acting. May see it as thin filaments and no Meyssan. And then the very end of both of these both ends are called the Z. Line or the disc. So let's look at this what this actually looks like. So here you have a circle mirror and it goes from here to here and the lines are here in blue, that's the Z. Disc. So then you have um the in line that's easily in the middle, you have the H. Zone. And so this is gonna be my sin that's not overlapping with acting. So here you have your medicine and red. So you can see that it's not overlap, overlapping of acting. Then you have your a band which has acting and medicine. And then you have your eye band which is much smaller and contains only this thin filament which is acting and that those are the structures that make up the circle mirror and you're gonna have to know them. It's gonna just be crucial. Um So those are the structures. So now let's move on.

Okay so now we're going to talk about the steps to a muscle contraction. And so if I'm just going to give a once in an overview of how muscle contraction happens. Well it happens because through the shortening of the SAR premieres that we talked about. So that's just the overview skeletal muscle contraction occurs through shortening of sarcoma years. But of course it's not that simple. And there are four steps that we're going to go over and then each or a couple of the steps have even more like intricate things we're going to talk about. But let's just go through them. So the first one is that the maya sin binds to acting. So it's a fairly easy step to remember. Then the second step is an A. T. P. Hydraulic sis step. And so a TB hydraulic sis of course, results in some type of change. And that change is a confirmation all change and that allows myosin to bind very tightly to acting. And this begins to stimulate the movement. So I'm going to talk about this but I'm gonna come back to this in just one second for the third step once the A. T. P. Has been hydraulic sized. What happens are these things called cross bridges which form? And this is going to be an overlap between the thin and thick filaments which remember the thin acting acting and mason. So there begins to be an overlap in the circle here and it overlaps because there's it's shortening so things are having to be condensed together and there's overlap and I'll come back to this and then the find the final thing that happens is that A. T. P. Binds again. This this associates the cross bridge and so it relaxes and elongates out again and returns to its relaxed stage. So let's go back and talk about these intricate things. So the first thing my sin binds to act in that's easier to remember. The second thing is the A. T. P. A hydraulic assist step and that allows my skin to bind tightly. So what happens is there's this other protein called Troppo mason. And this is a protein that normally and it's relaxed state is going to bind to the place the act in binding site preventing myself from binding there. But when a TB hydrolyzed this occurs, what happens is that um There's also another thing that happens which is calcium comes in and binds to this other protein called troponin. And when calcium is bound to your opponent that alters tre promicin. So you have calcium binding the proponent alters tre mason and then Tre mason um sort of moves a little and releases that binding site. So mason um can bind to act in or more tightly than it does. Then once it's bound really tightly you have across bridge form. Remember this is an overlap. So what happens is the eye band and the H zone shorten so that the Z. Line which is the ends come closer together. So you'll have to go back we look at the I. Zone or the eye band in the H. Zone, remember what these are? Um So that you know what thing is exactly shortening. So the length comes together. But the important thing here is that nothing is actually the length is not changing at all. Like the length of the mice and the length of the acting. They're saying exactly the same. The difference is that the acting is sort of just sliding past. So my hands right now same length. So if they come together they're still going to be the same length. But the distance between this wrist and this risk is now shorter because they slid past each other. And that's resulted in the stark amir shortening. So that's the same thing. So just like my hands don't change length when the when the risk get closer together and shorten the distance. Same here all the bands, all the action all the nice and stays the same length. It's just they come across each other and so they get shorter and then finally you get a tv binding which dis associates the cross bridge and returns to its relaxing. So here you have a relaxed state and you can see there are you know, big portions here that aren't over lacking you have an acting filament, you have your Z. Disc which is the very end here and here this is its relaxed state. Then all those steps happen and you have a contracted state and you can see that the bands are exactly the same length, but everything is now overlapped more so that these Z discs are closer together and it's more contracted. So let me also go over troponin and triple miocene which remember this is for step two. So here you have a filament here and an active filament which has troponin bound to it here and you have my sin which wants to bind so that it can contract. So what happens is calcium comes in and binds the troponin troponin, which then binds the troppo mason, which you can see is this green thing here which now I just made it blue. Let me highlight it this green protein here. This like thin protein that's overlapping this thin filament. So when calcium comes in, binds the troponin, troponin will change triple mason's confirmation and that will allow for mason to come in and bind the acting filament. So that is how that step two works. So with that let's now move on