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骨骼肌细胞可被分为两大类:慢肌纤维(I类)和快速收缩型(II类). I类肌纤维在长时间运作时更加高效.他们主要用来维持体位(比如保持抬头姿势),或者是需要耐久力的运动(马拉松).II类肌纤维依靠厌氧呼吸,短时间爆发力优于I类肌纤维,但也会更快疲劳.. Raja Narayan 创建




what's the difference between type 1 muscle fibers and the equally descript type 2 muscle fibers and I hate it when they give things names like type 1 and type 2 that's not really descriptive that doesn't tell me a lot of information about these types of muscle fibers so what I do is I get back at them I come up with one golden rule and this one golden rule will help me go through a table like we're about to do right here to differentiate between type 1 and type 2 muscle fibers so the golden rule I'm gonna have for this table here is that mitochondria mitochondria whoops look why I wrote that I their mitochondria are present in greater quantities in your type 1 muscle fibers type 1 so mitochondria are more prevalent in type 1 muscle fibers than in type 2 and just based on that knowledge alone we should be able to go through and fill out this table all right so let's start from the top I may have alluded to it here through the way I wrote this out but the color type 1 muscle fibers are often noted as red and why do you think that is well what our mitochondria used for mitochondria are used in biochemical processes that help us make energy and the main process they function in that I'm going to reference a couple of times is called oxidative phosphorylation oxidative phosphorylation now what does that term mean to you what does that suggest what are the two things that are probably involved in oxidative phosphorylation so just as the name suggests oxidative means oxygen is going to be evolved here and then phosphorylation means that something is going to receive a phosphate group phosphorylation something will receive a phosphate group so the oxidative part applies here to red the same way that the color red shows up in our arteries think about it why our arteries red and why our veins blue well arteries have more oxygen than veins do and because of that the color of our type 1 muscle fibers will be red because they produce more energy from oxygen than type 2 muscle fibers do more oxygen is present in type 1 so they're red and so we could say then that our type 2 muscle fibers will be white all right what about the speed of contraction that we see here how fast do type 1 muscle fibers contract well let's think about the process of making energy with mitochondria if type 1 muscle fibers rely on mitochondria for energy think about all the processes that have to go into making energy through oxidative phosphorylation you can't just do this right away you have to have glycolysis happen you have to have the Krebs cycle occur you need to make nadh and fadh2 all of these cofactors that have to go into this electron transport chain there's a lot of things that have to be done so mitochondria take a while to make energy so that means that the contraction speed here is also going to be slow because it takes a while to make that energy and so on the flip side that means that the contraction speed of type 2 or white muscle fibers is going to be fast what about the conduction velocity how quickly are we going to be able to receive a neuronal impulse or a nerve signal to type 1 muscle fibers to contract this is also going to be slow and the term here is called slow twitch slow twitch and I remember that the same way I remember that the contraction speed is slow in type 1 muscle fibers on the flip side we call type 2 muscle fibers fast twitch muscle fibers fast twitch all right now what types of activities do you think type 1 muscle fibers are going to be involved in well oxidative phosphorylation has another name the mitochondria is used for a specific type of respiration that's a cue term right there that's something that should cue another word in your mind if mitochondria is involved for a type of cellular respiration that type of respirable aerobic respiration requires mitochondria be present and so because there's more mitochondria in type 1 muscle fibers type 1 muscle fibers will undergo aerobic respiration what about type 2 well because they don't have as much mitochondria they're going to have to undergo an aerobic respiration or respiration in the absence of oxygen that's what aerobic means by using oxygen and aerobic means without oxygen okay how long will these muscle fibers be contracting well let's think about how much energy we're making if we have mitochondria versus if we don't have mitochondria we make a lot more energy if we have mitochondria and so the duration of contraction then will be long you're going to have longer contractions when you're able to make a lot more energy or ATP because you've got mitochondria present in greater quantities if you lack mitochondria or you undergo anaerobic respiration because you can't undergo oxidative phosphorylation as much you're going to have a lot of short duration contractions what's the difference between these two well if I'm having a long duration contraction that's something like the muscles in my back that I use for standing or in my legs so that way I can walk at a certain pace short duration muscle fibers those that contract really quickly and that's it are things like the ones in our arms when we shake somebody's hand or if we flick something with our finger if we do that for a long period of time we're gonna get really tired so these muscle fibers are not meant to be working for the entire day if we're in line at Disneyland we want to be using our long-duration muscle fibers the ones in our back in our gluts in our legs so that way we can stand for a long period of time we don't want to be standing on our hands or our fingers because we won't able to we we won't be able to last by using type 2 muscle fibers alright so which of these types of muscle fibers are most likely to fatigue well if type 1 muscle fibers are able to contract for a long period of time we say then that they are fatigue resistant they are fatigue resistant because we have enough energy for type 1 muscle fiber to contract for a long period of time but type 2 muscle fibers do not have as much energy because they don't have as much mitochondria and so as such they easily fatigue so all right easily right here they are not resistant what about the power of contraction that's associated with type 1 muscle fibers well I talked about some pretty heavy muscles just now the ones in your glutes your back and if we're having long durations of contraction these are going to be some pretty big powerful muscle groups and so all right strong here because again noting back to the mitochondria analogy if we have a lot more mitochondria present in type 1 muscle fibers they're going to have a lot more energy to contract and more muscles contracting more muscle cells contracting at the same time elicits a stronger more powerful contraction overall on the flip side type 2 muscle fibers not enough mitochondria not enough energy not enough power so these are going to be weak contractions and lastly how do we store our energy in type 1 versus type 2 this might be a little bit of a trick but you can figure this out with mitochondria we make a lot of energy and if we have a lot of energy are we gonna leave that sitting around as ATP no ATP is a really labile or a really reactive molecule if we have it there we're anticipating it to be used right away and so what type 1 muscle fibers do is that they store their energy in triglycerides these fatty substances and so that's why we put energy into fat so that way we can use it later on for these stronger longer duration contractions if we want to contract right away we'll just use raw ATP and so the ATP that's just sitting around is used in type 2 muscle fibers also we'll use something called creatine phosphate which is very similar to ATP in the sense that it has a phosphate group that it'll be able to donate to produce energy and so this phosphate group is very reactive very labile if it's sitting around that means it's going to be used any second now for a quick short duration action so by using this one golden rule here that mitochondria are more prevalent in type 1 muscle fibers we can figure out this whole table here and that's the difference between type 1 and type 2 muscle fibers