while in the previous video we talked about something known as the myofibril and I mentioned that the myofibril had these they had this unique quality of zones or areas where they were light and dark areas and I mentioned that the light areas were due to the thin filaments known as actin filament and myosin filaments were the reasons why it was dark because it was the thicker filament but what exactly are the actin and myosin filaments made out of right uh we need to talk about that a little bit too so what I'm going to do here is I am actually going to remove out one of the sections of the light area which is made out of the one Z line and the Z line and also the many actin filaments and I'm just going to highlight that one particular actin filament I hope you can see that over there where I have highlighted that in yellow and we are going to enlarge and try to draw out what we think the actin filament looks like because even by using an electron microscope when you try to magnify deeper into the actin filament you don't get um you don't get a very clear image because they are very tiny structures but based on Research based on scientific research we have an idea of what the actin filament is actually made out of and I'm going to try to represent it to the best of my abilities so to draw the actin filament the actin filament itself is made out of a globular protein called actin when I say globular protein what's the meaning of globular protein by the way chapter 2 as yes globular proteins just means proteins which are spherical or ball-shaped now you might be thinking how actin is a ball-shaped protein so how is it able to become an actin filament which is quite you know linear well it's very simple the many ball like proteins will just join together okay and fuse together you do not need to know how they fuse together there will be some calent bonds and such in play and that's what causes it to become that long structure known as the actin filament but the actin filament is not just that bare thing there are also other things that needs to be joined to the filament to make it become an actin filament other things also include something known as troponin and troponin over here I'm just going to talk about the function immediately but I'm not going to delve into the detail of troponin yet because we will talk about troponin in the subsequent videos more in detail so toonin is just basically another protein molecule that is attached to the filament and their function is just to act as calcium ion receptors just take it at face value for now I will elaborate on that in the future okay but also to complete the actin filament they must also have something called TPO myosin tropomyosin is just this fibrous protein which is usually like a linear shape now different books will represent the tropomyosin in a slightly different way what I like to do is I just like to represent the tropomyosin as something that is covering the bottom and the top of the actin filament so as you can see that covers the bottom it covers the top in reality it doesn't do that but I'm just going to represent it like that you just have to know that the function of the tropomyosin is to prevent the actin filament and the myosin heads from attaching to each other so of course when I teach this topic to students students will start to get overwhelmed because I'm introducing phonin which is a calcium ion receptor they might be thinking what does calcium ion have to do with anything and then suddenly they're thinking of oh Pho myosin myosin heads like what what the hell is this all about again calm down take a deep breath go get yourself a couple of coffee if you have to no coffee is a stimulant coffee makes us coffee makes it worse but you know what do what you have to do to Cal down a little bit so and then I'll say um don't worry about it because we have to introduce the myosin heads but for now the actin filament itself is made out of actin proteins joined together it's made out of something called troponin and also tropo myosin so sometimes in the exam if the question asks you to describe the actin filament I forgot which year it was they did ask it for like two or three marks to describe the actin filament you can actually say the actine filament is a thin filament thin okay that will give you one Mark you can say that it's made out of actin proteins phonin and Pho myosin I think for the most part that's good enough for the exam if they do ask you to describe the actin filament now what I'm going to do then is I'm going to take out the other structure you can see the mline and the mline is holding the thick filaments together and we know that the thick filaments are referred to as myosin filaments so I'm going to do a bit of changes just going to bring the acting filaments to the left because I need a bit of space okay the myosin filament is pretty interesting because I mean everything is I say everything is interesting uh because it is to me uh but some of my students will be like teacher it's not okay they they are just they're just having a headache at this point um so the myosin filament um what it does is I'm just going to draw it out again so what do we think the myosin filament looks like if we draw it out so as you can see that I'm just highlighting that green color area I'm just uh drawing out a magnified portion of what we think the green color area looks like so you know that the thick area over there that extension is the myosin filament the line that is 90° to it is the m line that's all good I'm now going to color it in with gray color okay that's all fine now the myosin filament itself uh on its structure it has this weird um I don't know how to describe it like a head like a ball or like an extension that is coming out like an like I guess many arms that are coming out many tiny arms or many tiny heads if you can call it that and those many tiny heads are referred to as the myosin heads the only thing I want you to understand about this myosin heads right now is it faces away from the mline you see the HS are leaning away from the mline it's not leaning towards the mline so immediately some of my students will go ah when you mentioned phom myosin you talked about the myosin head right I'm circling that okay can you see that in green and now I'm introducing something called myosin heads so something needs to happen between the actin filament and the myosin heads during muscle contraction so you must understand that there is a connection between the two of them obviously and we will talk about the connection between the two of them in the next video another thing that we also have to mention here is at least just to put it in your notes when you're writing your notes is this the myosin head also has this particular characteristic where even though it looks like this globous structure is like a head right and it has something to do with the actin filament later they can act as enzymes too what I mean by that is they can actually receive ATP molecules and they can also attach the ATP molecules can attach to them and they can also hydrolize ATP into ADP and phosphate so the myosin head can act as something called ATP a ATP a is a type of enzyme that have the function of hydroling ATP why do they have to do that again future future future f future okay so don't worry about that the reason why I'm trying to keep these videos as short and as concise as possible is because I want to introduce very simple Concepts first because if I did one entire video on skeletal muscle number one it's going to be more than 40 minutes to 50 minutes I think and number two it'll be too much as well so I think i' rather break it down into digestible chunks at least