Muscles

Muscles


Hi, this is dr. Claire and this is our lecture on animal muscles so one of the things that makes animals Kind of different from a lot of other organisms on the planet is that animals can move they can Get around they can run after things they can Chase each other and mate and eat each other and play and do all kinds of other things And what allows them to do that is? Among other things the muscles in their body, so we’re going to be talking about muscles for this lecture all right so In vertebrates at least there are three major types of muscle tissue There is smooth muscle cardiac muscle and skeletal muscle and So smooth muscle is found largely in the linings of the intestine in on the linings of the blood vessels that allows us to dilate and contract blood vessels and various other internal organs Smooth muscle muscle is not under our conscious control We can’t think about smooth muscle and make it contract But it does it is under the our it is under our neurological control in our subconscious, so it does Allow us to do things like move food through our bodies Control blood flow to various parts of the body things like that okay? Smooth muscle cells are called smooth because they appear smooth they do not have lines along them Which you’ll see in some of the other muscle tissue types We’re going to look at and each cell has a single nucleus They tend to be very long and skinny and they contract in the direction of that long and skinny axis so if you look at something like our intestine There’s actually several layers of smooth muscle some that run along the length of the intestine and those ones Allow the attested to contract longitudinally And then some that are around the width of the intestine and that is a lot of the intestine to contract in that dirt, okay The cardiac muscle, that’s muscle tissue. That’s found in the heart cardiac muscle tissue Does have striations on those striations are? Divisions within the cell we’ll take a look at those a little bit more when we look at skeletal muscle cardiac muscle cells tend to be Kind of branched and interconnected each. Cell only contains a single nucleus They’re extremely efficient and extreme have extremely high endurance and this was allows your heart to beat every few seconds or more than once a second for your entire life, so They are an extremely efficient muscle for that reason Okay, so that’s cardiac muscle skeletal muscle is all of the other muscles that are attached to your skeleton that are under your conscious control Okay, so they are different from the other two muscle types because they are under your conscious control they also do have striations, which I’ll show you in a second and They are Multinucleated, so here’s what skeletal muscle tissue organization looks like you’ve got these bundles of muscle tissue That within each muscle There’s there are even smaller muscle bundles that are held together with some connective tissue And then these smaller muscle bundles are made up of single muscle fiber cells again Here’s the multi nuclei nucleated Cell there with a couple of different nuclei on in purple there and then within each of those cells there are what are called myofibrils these are little fibers of muscle material within the cell and those myofibrils are actually made up of Smaller subunits called sarcomeres that are made up of a couple of different proteins Myosin and actin that are what’s actually doing the contracting within the cell and the sarcomeres have distinct lines between them and so That’s what gives the muscle its striated appearance, so that’s why it’s sometimes called striated muscle and so this kind of Nested Organization of the muscle fibers allows these muscles to function very efficiently so let’s take a closer look at a sarcomere So taking a closer look at the sarcomeres here. They are these these two different fiber types They have there seen Myosin fiber and the actin fiber the myosin fiber is slightly thicker It’s shown here in blue the actin Fiber is in red and slightly thinner the myosin fibers have these little headset come off of them So if we take a closer look in at these different types of fibers This is a single Myosin molecule here in the middle with the little head poking off And then the myosin fiber is a bunch of those molecules all clumped together with these little heads poking off and these are the Acton’s as this little filament of interwoven Acton’s That that come together and so the way that these these filaments interact is that they actually slide past each other so when the muscle contracts the Actin filaments and the myosin filaments slide past each other to contract the muscle and the way that actually works It’s those little heads on the myosin fibers. They bind to the actin, and they kind of pull it along like a little kind of like a little caterpillar pulls it along each of those little actin heads kind of Nudges it along and that’s what allows the muscle to contract and then when it relaxes. They go back the other way, okay So that’s what’s happening it and as they slide past each other the muscle gets shorter in that direction and so the little striations of those either the Z-disks here the striations that you can see in the muscle. They get closer together as the muscle contracts, okay? so That contraction of course the force that’s caused by the contraction Is the greatest when a lot of those little myosin heads are in contact? so there’s a kind of an optimal level where the Actin and myosin are overlapping enough that there’s a lot of those heads in contact And that’s when you’re going to be able to exert the most force with your muscle if the muscle fiber is more stretched out Whew there’s going to be a little less overlap between the actin and the myosin and so there’s going to be less force And if it’s too overlapped then the myosins are going to start or throw the Acton’s are going to start to run into each other on the sides and again You’re going to have not as much contact between the actin the myosin so you’re gonna lose force on the other side as well So there’s kind of a happy middle of the amount of muscle Contraction where you get the most force on the muscle? Another thing that influences the force of the muscle is the speed at which it is shortening So if you’re looking at say your bicep as you move your forearm towards you you are shortening this muscle In the biceps so there’s force that can be exerted as the muscle shortens There’s force it could be you can resist force while keeping your muscle the same length that’s what we call Isum isometric contractions, and then you can actually also look at force exerted while the muscles lengthening and Actually the greatest amount of force that you can exert is actually while the muscle is lengthening that allows you to do things like Gradually lower heavy items to the ground hike down. Hill as your body is going downhill You have to slow your slow your speed And so that that is actually where you get the greatest force and the muscles as they’re Lengthening rather than as they are contracting, and if you want to contract them faster You can only apply a small amount of force so if you’ve ever tried to Lift a very heavy thing you may notice that you can only lift a very thick heavy things slowly And you cannot lift it fast That’s because you can’t exert enough force as the muscle is contracting rapidly to lift that heavy thing quickly ok another thing that that affects the the muscle function is The direction in which it pulls so muscles are connected to your skeleton And so you have one muscle that is going to move your bicep up and as can can apply force in this direction You that’s your bicep on the other side of your arm you have your tricep and that can apply force in a downward direction? Right and so these two muscles act Opposite each other to allow you to move your body and that’s similar in lots of other parts of your body as well So another difference in the muscle fibers in the body is that you have some muscle fibers? Which are what? We call fast twitch muscles and some muscle fibers, which are what we call slow twitch muscles fast slow twist muscles Use a lot of oxygen. They’re really good at aerobic activity, so sustained long long-term activity and Using a lot of oxygen for that activity Fast-twitch muscles they are good for short bursts of speed or strength And they can run pretty well without oxygen for a period of time, but they will quickly become fatigue fatigue So it’s kind of a trade-off between the short the fast twitch and the slow twitch muscles fast which is really good for bursts of speed bursts of strength slow twitch is good for endurance and Long-term function and so different parts of the body may have different proportions of fast and slow twitch muscles different people may have different Proportions of fast and slow twitch muscles so if you look at a marathon runner in their legs you’ll find mostly slow twitch muscles Which are really good for endurance running? And they can run a lot good speed for a long distance in a sprinter You’re going to find a higher proportion of fast twitch muscles, which can Propel the Sprinter very fast, but for a very short period of time okay And if you look into animals you see a similar pattern, so you probably probably familiar with light and dark meat chicken And the reason why the legs on the chicken are dark meat and the breasts on a chicken is light meat it’s because the legs are slow twitch muscles and the breast is hyped as fast twitch muscles so the Legs of a chicken chickens spend most of their time wandering around Looking for food scratching at the ground and so they need good endurance In their legs for running around and all day long occasionally a chicken gets scared, and it needs to escape and so the the breast muscles are good for a quick burst of flight to escape away from the potential predator But they don’t need a long endurance chickens are not going to be flying long distances chickens Do not migrate and so the the breast muscles is all fast twitch muscle And it doesn’t need as much oxygen so it actually has less oxygen binding iron molecules That’s why it’s lighter colored and it allows that you can do very quickly escape very quickly have a quick strong response But it’s not good for endurance if you look at some a different bird like a duck For example that spends a lot of its time swimming with its legs, but also migrates Thousands of miles using its breast muscle it has dark muscle both in its leg and in its breath So hope you enjoyed this little lecture on muscles, and I’ll catch you next time

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