all right Niners in this video we're going to talk about the skeletal muscle fiber types okay so when we take a look at a skeletal muscle you know most people think just oh it's just muscle fibers well technically those muscle fibers or those muscle cells they differ okay so for example what I wanted to show you before we get into each one of these actual muscle fiber types that way I can actually like completely clarify something let's say I take the actual muscle if you guys remember from the structure of skeletal muscle video we took and and took the section of a muscle belly then we had around we had inside of the muscle belly we had those bundles of muscle fibers called a fasle well right here this whole bundle here a cross-section of it this is our fasle so this whole thing right here is specifically the fasle now in this fle there's consisting of multiple muscle fibers now the thing is is that each one of these muscle fibers are not all the same they can differ so for example we're going to talk about three main types of muscle fibers type one type 2 a and the last one which will be type 2 x now some people will be like oh well what about type 2 B type 2x is mainly in humans type 2X X is in other I'm sorry type 2 B is in other different types of animals so in this video we're going to talk about type one type 2 a and type 2x tissues okay or skeletal muscle fibers so when I actually look at each one of these structures it might look like a big muscle but technically what I'm trying to represent here is that this is a muscle fiber type this is a muscle fiber type and this is a muscle fiber type okay so that we're clear all right so first thing we're going to do is we're going to start here with this skeletal muscle fiber type and we're going to denote this one to be type one okay so this skeletal muscle fiber type is specifically type one now here's the thing type one skeletal muscle fibers also have another name and we we'll decipher that name as we go through its different types of structural characteristics and metabolic characteristics and really what it's functionally uh for and that name is called slow oxidative muscle fiber okay so this is a slow oxidative muscle fiber and sometimes they even add on to it they say red slow oxidative I'll do that just for the heck of it I'll put that right here it's technically red slow oxidative that's really going to help us to decipher what makes this skeleton muscle fiber type different from the other two skeletal muscle fiber types all right the first one let's go ahead and go through each one of these uh skeletal muscle fiber types in a specific order okay so structurally how is this type one skeletal muscle fiber different from these other two well the first thing about its structure is that if you guys notice this muscle fiber is a lot smaller than the other two so because this muscle fiber is a lot smaller than the other two it should be the smallest muscle fiber so its overall fiber diameter should be a lot less so in that that's the case then the fiber diameter should be very small so it should have a decrease or a small let's say let's actually not put decrease let's put small fiber and all fiber is just a muscle cell diameter because that's one thing so if you look at the diameter of this guy as compared to all the rest of these it's a lot smaller d diameter okay that's one thing what else is structurally different from this one all right let's look at it's name red what is the red really coming from now muscles are highly vascular highly vascular but specifically the most special type the most highly vascularized muscle fibers are the red slow oxidative muscle fibers they have a large amount of capillary density so if that's the case then let's say I represent this with a blood vessels right so if that's the case then this is going to have a large amount of blood vessel Supply this is going to have a large amount of capillary Supply if this has a large amount of capillary Supply then what does that mean for its actual color that means that its color is going to be a nice bright red why is it going to be a nice bright red the reason why it's going to be a nice bright red is because it's carrying blood through there right so if it's carrying blood through there what's special about blood blood is having hemoglobin in it and hemoglobin is actually what causes the actual blood to look red specifically red blood cells so it's having a lot of blood flowing through that area so because there's a lot of blood so let's represent blood flowing through here and out here what type of color is it going to give off it's going to give off a nice reddish color and the reason why is because this has a high capillary density so a very high capillary density and then again if that's the case then if it has a high capillary density what color would you expect this actual skeletal muscle fiber to exist as it would be very very red because there's a large amount of capillary supplying it so if that's the case then it's going to have a nice reddish Hue and huge is is kind of you know color all right so nice reddish hue okay so what do we know right now first thing we know smallest diameter muscle fiber second thing we know high amounts of capillary density so a lot of blood supplying this muscle fiber because there's a lot of capillary density it's going to have a nice reddish Hue and also think about this if you have a small skeletal muscle fiber does it take as many capillaries to actually uh cause that reddish Hue on that that structure no if I take a big huge skeleton muscle and I have a decent amount of capillary density it's going to take a lot of capillaries in order to produce off that reddish Hue on a large skeletal muscle fiber as compared to a smaller skeletal muscle fiber so a smaller skeletal muscle fiber even though the capary capillary density is really high it doesn't take as much capillaries to produce that nice reddish Hue as compared to a large skeletal muscle which require significantly large amounts of capillaries to produce that same reddish Hue okay that's that part next thing I want to talk about what about organel in this area what about the organ LS there's a very important organel that is important for these skeletal muscle fibers okay this organel is specifically the mitochondria so let's have here the mitochondria this one has a significant amount of mitochondria very very significant amounts of mitochondria now that's important and we're going to talk about that when we get into the metabolic characteristics of these guys but again I want you to understand that this one has significant amounts of mitochondria now what are mitochondria important for if you guys remember mitochondria are really important for ATP production they're the powerhouses of our cells right so because they're the powerhouses of our cells what are they basically doing if you guys remember they can take certain types of energy sources like what they can take glucose they can take amino acids they can take fats right and what can they do with that they can utilize that and do what use that in the presence of what has to be there though in order for this reaction to actually occur you need to have oxygen you need oxygen what does that mean when you need oxygen when a pathway requires oxygen it's an aerobic pathway so it's an aerobic pathway and the overall result out of this is that'll lead to the formation of ATP so if that's the case and if these guys need oxygen and they're metabolizing fat fats and glucose and amino acids to be able to produce ATP and you they have plentiful amounts of mitochondria what does that mean for the ATP formation they're going to have a decently High ATP formation so these types of skeletal muscle fibers generally produce a significant amount of ATP by cellular aerobic cellular respiration but let's come back again what did I say about the mitochondria so that we can continue to keep labeling here we said that there's a decent amount of mitochondria so they have a significantly large amount of mitochondria so large amount of mitochondria okay so now that we've done that we can relate the Structural Concepts to the metabolic Concepts here okay first off we talked about mitochondria what did we say was one of the metabolic characteristics here because they have significant amounts of mitochondria they're primarily going to be depending on oxygen so the primary way upon which these cells produce energy or ATP has to be aerobic cellular respiration so these skeletal muscle fibers primarily depend upon uh aerobic cellular respiration okay so for example they would use they would undergo kreb cycle they would undergo the electron transport chain reactions they would undergo many many different types of reactions and lead to the production of ATP by what type of process are they producing ATP this is under oxidative phosphorilation okay so that's one thing we know that they're very very dependent upon aerobic cellular respiration another thing because these skeletal muscle fibers are small They Don't Really and oh before we even do that what what does their name suggest red okay that means a lot of capillary density it means something else in a second slow oh you know what these these muscle fibers must contract very slow and that is true these skeletal muscle fibers are the slowest in contractility speed so the rate at which these muscles are Contracting are very slow and we'll see why here in just a second so again what is up with the contractile speed here very slow contractile speed so the rate of contraction is a lot lower in this skeletal muscle fiber type and the reason why is it has a decreased mein atpa activity okay we talked about this a little bit in the actual skeleton muscle contraction video If you guys remember let's say here I have thin filament and on the thin filament you have actin and if you guys remember we had the thick filament right and the thick filament specifically consists of these mein right with the mein heads that were connecting with the actual actin remember in order for us to detach the myin we had to bind ATP but then what else did we say remember we told you that in the first step of that whole process there was hydraulis what does that mean to hydroly the ATP well you remember we said that it actually is breaking the second and third phosphate that bond between those two there's a special enzyme that's actually on the mein on this mein it has a special enzyme component and what that enzyme component does is it actually breaks that bond between the ATP and then converts it into ADP and anorganic phosphate which helps to be able to put it into that cocked position right this enzyme that's a component of the mein that enzyme so imagine again if I draw it over here on the side imagine here is the enzyme okay and this enzyme is actually a part of mein it's actually a component of the myosin and what happens is it's breaking down the ATP what is this enzyme called this enzyme is called aasin ATP now think about this for a second if there's the activ ity of this enzyme is decreased will he break down as much ATP no if he doesn't break down as much ATP will he be able to detach the myosin from the actual acting very quickly no if he doesn't detach it will he be able to will he um will the will he be able to cause the cocked position and then reattach to the next actin quickly no and so then will he be able to create the power stroke quickly no so the overall concept is is that because he's decreasing the meas and atpa activity this whole Detachment and then hydrolysis and then the whole power stroke and then rep putting on the ATP that whole activity the sliding filament theory is going to decrease therefore the contraction speed will decrease another thing to think about if it's undergoing aerobic cellular respiration doesn't it have to go through many many different types of Pathways so it might take a little bit longer to be able to produce significant amounts of ATP because you know there's two types of phosphorilation substrate phosphorilation and oxidative this cell primarily depends upon oxidative and oxidative we already said produces very significant large amounts of ATP okay next thing about this uh skeletal muscle fiber we know that it contracts slowly we know that the speed is very slow but here's what's really cool about this muscle because it contracts slow it can last a long time okay so because it's Contracting very slow the activity this skeletal muscle fiber can go on for a long period of time not only that think about energy- wise if I have enough energy I can carry out an activity for a decent amount of time but if I don't have enough energy that activity won't be able to go on for a very long time so what two things are contributing to this muscle being able to carry out this activity for a long time one is the slow contractile speed and the other one is the large amounts of ATP produced so therefore we can say that this one is is actually going to be fatigue resistant very very fatigue resistant high amounts of fatigue resistance so this muscle can go on for a long period of time can carrying out its activity if you really want to know it can carry out this activity for hours many hours okay okay but here's the thing because it's fatigue resistant it actually is not going to be very strong it doesn't generate a lot of power and that should make sense because of this decreased mice and atpa enzyme so because it's smaller a smaller diameter fiber and because of this mice and atps activity and the slow contractile speed it's not going to be able to generate a decent amount of power to move a heavy load so therefore because it doesn't have a lot of power do you know what's called there's what's called a motor unit what is a motor unit what is a motor unit a motor unit is two things it's a motor neuron and all the muscle fibers it's supplies now there's What's called the size principle the what with the recruitment concept and recruitment just means if you have a motor unit if you have more motor units you can recruit more muscle fibers but now let's look at the side let's look at the aspect of the muscle fibers okay now if we look at this from the respect of the muscle fiber concept not the motor unit concept if we want to be able to move something right something you know really really heavy it's going to require okay a specific type of activity but these muscles are very special and the reason why they're very special is they're not used to carrying very heavy loads they're so because of that they're not used to carrying very heavy loads these muscle fibers are going to get recruited first okay they're not used to carrying heavy loads so the order of muscle fiber recruitment in other words the motor units so the motors neurons that are actually stimulating those muscle cells to contract this muscle fiber will be the first one to be stimulated so type one muscle fibers are red slow oxidative muscle fibers are the first muscle fiber to get recruited and the reason why is it produces very little power so because it produces very little power you don't really need this muscle to be recruited last you just want to get through that muscle quickly and then move on to the other types of muscle fibers okay so this is the one that gets recruited first so again if we have a motor neuron here and here's your motor neuron this motor neuron will actually recruit this muscle fiber first so it under goes first recruitment okay so this is the first recruitment muscle fiber next concept okay now this skeletal musle fiber is going to be depending upon oxygen and one of the pathways that requires oxygen a decent amount of it and what's really special about this muscle fiber is because it doesn't undergo Anor robic processes it's going to depend upon oxygen and it's going to store a special type of storage molecule and that storage molecule is called triglycerides it's called triglycerides and these muscle fi types are very special because they store a lot of their energy in the form of triglycerides and if you guys remember we talked about over here with fats what do triglycerides actually do whenever they go into the mitochondria if you guys remember when these guys go into the mitochondria they undergo a special process and that special process is called beta oxidation right specifically the fatty acids and when they undergo this beta oxidation what can come out of this result this you can produce tons of ATP and again this is the result of beta oxidation specifically for the fatty acids and then the glycerol can actually go into a spe specific glycolytic pathway and that glycolytic pathway will also lead to the production of ATP now again if we're looking at the skeleton muscle fibers their main source of energy storage of fuel is in the form of triglycerides so how do they store store their energy they store their energy primarily in the form of triglycerides that's their main source of energy storage is in the form of triglycerides now one more thing you know the skelet MUSC have a special protein a special protein that it has within it this special protein is something like hemoglobin it's something like hemoglobin it's not hemoglobin but it's something like him and this protein is called myoglobin you see this protein here this it's smiling at you because it's helping us right all the time helping out your skeletal muscles this protein is called myo globin and what myoglobin is really cool at being able to do is it temporarily holds on to the oxygen so whenever blood is flowing through this area it drops off oxygen to this myoglobin and the oxygen can bind onto the myoglobin and Ami globin can hold on to this oxygen and whenever the tissue cell needs it it can drop that oxygen off right so whenever it's actually relaxing the blood is coming to the tissue is dropping off oxygen when the skeletal muscle gets ready to contract right we need ATP so what do you need in order to produce ATP oxygen the oxygen can get used to produce ATP so we need to have a lot of myoglobin so the amount of myoglobin and the skeletal muscle fiber should be very very high so we should have a lot of myoglobin too okay all right so because these muscle fibers are having to be able to specifically produce lots of ATP they contract very slowly they're very fatigue resistant you're going to want these to be muscles that you can carry out some activity for a long period of time so one of the things that most people you if you think about is marathon runners so this is very good for those people who are going to run marathons so if you're one of those individuals who wants to go and run a marathon okay so run marathons these are some good muscle fibers that are going to help you in that process and the reason why is because you know marathons I've never ran one but I from what I understand you run long distance right and so because of that you're going to require a lots of ATP production because your skeletal muscle fibers are going to depend upon that ATP in order for us to do that we have to have a lot of aerobic cellular respiration not only that but these muscles are very fatigue resistant because they have a high capillary density a high amount of oxygen coming to the area right and they have lots of triglycerides is a concentrated source of energy fuel so because of that that's one thing but you know what else is really important think about this what is what is always always pushing down on us gravity so because gravity is always pushing down on us naturally it would want to push our muscles like this right so because of that we have muscles that are constantly helping us to maintain posture and maintain our body position so those muscles that are are anti-gravity or posture muscles are also really important because they have to do do that all day so if you're standing up a lot if you're having gravity push down these muscles are constantly helping you to maintain your normal body posture so again we can say anti-gravity muscles or posture muscles so anti-gravity muscles and those would be a great example of your posture muscles okay helping to maintain that nice posture okay that's our type one are red slow oxidative muscle fibers