Musculoskeletal System

I In this lesson, we'll be talking about the musculoskeletal system which is made up of the muscle system and the skeleton. Now the muscle system is an organ system that is made up of muscle and it's going to include skeletal cardiac and smooth muscle, which are different types of muscle muscle is just a tissue that can contract due to an interaction between acting and mice. And that will take a closer look at later. Muscle cells are called maya sites and that prefix myo generally refers to muscles. Now there are specialized types of maya sites that you'll find in skeletal cardiac and smooth muscle. But you don't need to worry about that just yet. Now, here we have a nice overview of the human muscle system and here we can see just a few individual muscles and how they are connected to bones. Behind me. Here we have a Maya site. This is a muscle cell and you might notice that there is a nerve that is forming a connection with it. We'll talk more about why that is later. Now the skeleton is going to be the support structure of an organism and it's going to work with the muscles to produce locomotion. Now some organisms have an external skeleton called an exoskeleton. This is common in arthropods, like this awesome rhinoceros beetle. You see here we humans on the other hand have an endo skeleton which you can see here and this is an internal skeleton that's gonna be made up of mineralized tissues like bone bone is this rigid mineralized organ. We'll talk a little bit more about later, and muscles and bones are going to be connected to allow for voluntary movement. We call this movement locomotion. You can see pretty awesome example of that in this cheetah, right here behind me. With that, let's go ahead and flip the page.

muscle is made up of many muscle fibers. As you can see here in this diagram, these air long, thin my oocytes that actually contain multiple nuclei and they're going to be chock full of what are known as my oh federal my A fib. RL are these rod like protein structures that are going to be made of acting and my Yasin and these air What are going to do the contracting Now they're going to be arranged into units called Sarka Miers And these air essentially the Contract I'll units that will be chained together and formed longer. Myo Federal. So each SAARC Amir is gonna individually be contracting so that the longer Myo federal itself contracts now striated muscle like skeletal muscle in cardiac muscle gets its name. Because of these repeated units, notice sarka meters that give it a sort of lined pattern. Hence striations. Now SARC Amir's are going to be made of what are called thick and thin myo filaments and these air going to interact by sliding past each other to cause contraction. Now my Ofili mints take two forms. There are thin filaments which are made of acting and thick filaments that are made of Maya Seuin They're going Thio be joined together these Sark Amir's at what are known as Z discs. So here you can see our Sark Amir Hopefully you can seethe lined pattern in there The striations, if you will. And these dark lines are the Z lines. So what's between these Z lines or Z discs? Uh, either name really works. What's between These is one Sark Amir, and it's going to be made up of thes thick filaments that you see in blue here and thes thin filaments that you see in red and those air What? They're going to slide past each other to cause contraction like you see happening behind me here the thin and thick filaments are a little more spread out right. There's a little more distance here and here they are contracted. That's gotten a little bit smaller because essentially, what's happened is this Ah, they've moved past each other in this direction and we're actually gonna flip the page right now and take a look at how that happens.

the mechanism that explains how the thin and thick filaments slide past each other to cause contraction is known as the sliding filament model. Now it's going to involve some proteins that interact with acting filaments. You see, these acting filaments are actually going to have binding sites for my assassin along their length. But normally these Mayas and binding sites are going to be covered by this protein called trope um, IAS in, which is basically wrapped around acting to block these Mayas and binding sites. And it's also gonna have this attached protein called troponin and this is it going to be a calcium sensitive protein that when it binds calcium, it causes the trope, um, Eliasson toe actually move and exposed the my it's, um, binding site on the acting filament. Now we'll talk in a little bit about where this calcium comes from, so for now, I don't want you to worry too much about it. Just know that it's going to be due to, uh, an action potential hitting the neuromuscular junction and that that's, you know, essentially, just think of it as a synaptic signal that's going to trigger this calcium release, and we'll go into the details in just a little bit. Now the Maya Seuin filaments have what are called Miocene heads there. I like to think of the Maura's like grab the arms or something and these air what air going to be used to sort of pull the myson along the act in filament. Now, when the troponin binds, calcium causes the trophy Maya's into expose those binding sites on acting, the myson is going to attach to the acting filament. Now it's It's actually only gonna attach if it has a teepee bound and if it has eight p bound, it will go ahead and attach to the acting filament like you see happening here. Let me actually go ahead and number of these for us. So that's gonna be a first step. Second step, and then right behind me, jumping out of the way. You'll see Step three. This is where that 80 p is going to be hydrolyzed and trigger what's known as the power stroke. Now, that's basically gonna be this uhh sort of shape change in the Miocene protein that you see here where it hide. Relies is the 80 p and releases the phosphate and the ADP, and it causes the head. Thio essentially move in such a way that it it pulls itself along the acting filaments. So here you can see they're trying to show the difference in the angle that it takes. Same with what's going on here. So essentially, that head is going, you know, from this position, thio this position so it'll move. You know, this distance more or less. And once that a deep gets released like we see happening right here in panel five, Uh, the myson is actually going to bind another 80 p and release from that acting filament like we see happening here in panel six. Now, this is essentially one little step that will have to be repeated many, many, many times to cause, you know, the big muscle contractions like, you know, I mean, even just this is, uh, needs, you know, a bunch of those power strokes toe get my get my muscles toe crank like that, you know? So the point is, this is going to be repeated many, many times. This just causes, like, one little movement. But you add a ton of these together, you know, in all those Arkham ears, and then you actually see a big movement as a result. So with that, let's go ahead and flip the page.

a motor unit is composed of a single motor neuron and the muscle fibers that it controls. The connection between the motor neuron and the muscle fibers is known as the neuromuscular junction. It's basically a synapse between neuron and a muscle. And here in this image you can see an example of a motor unit. Here we have our motor neuron. This is our neuromuscular junction right here inside. You can see all of these little myo filaments, and this whole thing here is a muscle fiber. Now, the muscle fibers of a motor unit are going to contract as a group. The nerve is going to release a Seattle coleene Lin. An action potential comes and this is going to stimulate muscle contraction. And the way that works is basically a seal Colin will bind to receptors on the other side of the Neuromuscular junction. Thes are called nicotine IQ receptors, in case you're curious, and this is gonna lead to deep polarization through excited Torrey post synaptic potentials. And that is going to cause an action potential that will actually travel into these indentations in the membrane called trans verse to Buell's. And that's gonna pull these action potentials into an area known as the Sarka plasmid. Ridiculous. Um, and this is basically a special type of smooth, smooth and a plasma critic Ulan that's found in my oocytes and the action potential will travel down these trans verse tubules and cause the sarka plasmid ridiculous, um, to release calcium. That's how this calcium is gonna get in there to bind to the troponin caused the trope Miocene to move out of the way. Uh, for the myson fill our heads to bind to the acting filaments. Now, after this is done, the calcium has to be pumped back into the SAARC. Plasvic ridiculous. Um because, you know, you need to be able Thio essentially make these discreet contractions, right? The nerves, they're gonna be sending discrete signals. And so we need to be able to have discrete muscle contractions. We also don't want to have permanent, uh, you know, contraction, permanent tension. Now, here you can see you know, an example of that action potential moving down this trans verse tube, you'll or T tube you'll as it's sometimes called, and this is going to lead to calcium release that will lead to contraction. You can see here. So with that, let's go ahead and turn the page

on action potential will cause muscle fibers to twitch, as it's called, so a single action potential results in a single twitch. Now the tension, the difference intention that you can create in your muscle is due to action potential frequency. So the higher the frequency of the action potentials, the more tense the muscle will become. And this can actually lead to something known as tetanus, which is sustained muscle contraction because the twitches fuse together. Now you can see a model of that happening here where we have an action potential, this red spike. And then here in blue, we have the twitch of the muscle, and here you can see the frequency of action potentials. Each one of these lines is an action potential coming in, and here you can see the resulting tension, how the frequency of the action potentials is actually going to cause the tension to increase. Now there's actually different types of fibers designed for different types of twitches. There are what we call fast twitch fibers that contract very rapidly and slow twitch fibers that contract slowly. Now. The reason you want both of these is they serve different purposes. Those fast twitch fibers contract very quickly, but they'll tire out quickly as well. And this is in part because they rely on, uh, a teepee from like Allah assists instead of aerobic respiration, which is going to allow them to get a lot of ATP really quickly. But it's not going to be as sustainable because aerobic respiration provides a much higher yield of ATP. Now these slow twitch fibers can sustain longer contractions. They're not gonna tire out as quickly. And they are going to contract mawr slowly due to a, uh, the rate of 80 p hydrology sis in mice. And that's what's actually going to control that, or what's going to cause it to actually slow down. Now muscles contain a special oxygen binding protein called myoglobin, like hemoglobin, for example. You know, similar similar idea there, of course, it's, um, gonna be a bit different from hemoglobin. However, it's an oxygen binding protein, Um, and its purpose is to actually store oxygen so that when the oxygen demand and muscles is very high, and perhaps that hemoglobin can't provide everything they need, we have this store in myoglobin. Now there are different types of muscles, and they could be grouped based on whether they're controlled by conscious thought or unconscious signals. So voluntary muscles, which are controlled by conscious thought our, uh, skeletal muscles and these air going to be those strident muscles made of long my A fib. RL now, involuntary muscles are, as we said, controlled by unconscious signals and thes. They're gonna be regulated by a division of the nervous system known as the autonomic nervous system. Now they're gonna be two types of involuntary muscles smooth muscle, which actually doesn't contain my A fib, rials. And these are going to line blood vessels, the digestive tract, and they're going to be responsible for parastatal sis. So these air actually a very important type of muscle, Um, just made of, you know, little individual cells that will contract in, you know, a different way than these my A fib roles. They'll still use those acting in mice and interactions, but they're not gonna have these long chains of SAARC. Amir's that are, um, you know, going to chain together those contractions now, cardiac muscle is striated, and it, uh, contained you know, it's dry it So it contains Sark Amir's. However, it is on involuntary muscle. You don't have conscious control over your heart rate. Um, and it's gonna have this special feature known as inter kill ated discs. Thes are basically like, uh, they're gonna have gap junctions. More or less. There's a little more to them, but they involve gap junctions, which are those direct connections between cells. And that's gonna allow action potentials to spread through the cardiac muscle. And this is gonna be very important for heart contraction, which relies on the spread of these action potentials flowing through the heart. Thio create the rhythmic heartbeat. Now with that, let's go ahead and flip the page.

the vertebrate endo skeleton is composed of bone, cartilage, tendons and ligaments. Now, bones are made of basically cells in this very special hard extra cellular matrix that contains calcium. Now, as you can see, there are many different types of bones. Short bones, flat bones, structural bones. And we're going to take a look at long bones, you can see a long bone right here. And what's special about long bones is they have this mega larry cavity which is going to contain red and yellow bone marrow and that's going to be very important for the production of blood cells. Now there are some special cell types and bones that I want to mention and those are osteoblasts and jump out of the way here. Osteoclasts. Osteoblasts are going to form bone and osteoclasts are going to re absorb bone and these cells are going to be involved in blood blood calcium, homeostasis, the endocrine regulation of it through the hormones, parathyroid hormone and calcitonin. And if you want to know more about that, recommend you go check out our videos on the endocrine system with that. Let's go ahead and flip the page

cartilage is this elastic tissue containing collagen proteins. And for some organisms, it's actually going to be the main component of their skeleton. For example, uh, sharks now it's also going to be, um, important component in tendons and ligaments, which are types of connective tissue that, uh, in the case of tendons, link muscle to bone and, in the case of ligament ligaments, link bones together or link bone to bone. And you can see example of that here where we have a tendon connecting this muscle to this bone. And here, where we have a ligament connecting this bone to this bone. Now joints are what we call these connections between bones, and they're gonna actually allow for specific types of movements. Now there's many different types of joints. However, I want to mention to those air ball and socket joints thes gonna be like your hips and shoulders where you basically have a ball that fits into a socket, and it's going to rotate around in there. And what's nice about ball and socket joints, as I'm sure you know with your arm is you can really get a lot of range of motion on that now In contrast, hinge joints limit movement to a single plane, but these were usually able to generate more force and a nice example of a hinge joint. Is this joint we see right here in your leg right now. As you can see inside this joint, we're gonna have some nice cartilage that's going thio Protect those bones from rubbing on top of each other, which would have been which would be rather very, very painful and is actually the cause of some types of arthritis. Now, muscles and bones work together in basically what you can think of as antagonistic pairs and that this is not always the case. But many muscles work together in these antagonistic pairs. So I want to show you one example of how you know muscle and bone come together to produce, you know, different types of movement. So here we have a wonderful example of an antagonistic pair that we're all familiar with, and that is the biceps and the triceps. And you can see that the biceps, when these muscles tense, right when they pull, they're gonna pull these bones closer together, right? That's why we call them extensive er zits a muscle that basically Ben's a limb and pulls it close together. Now these air gonna work in opposition to extend. Sirs, this is the that antagonistic pair. The extensive is the antagonist to the flexor. The extensive er when it contracts is going to straighten and extend a limb. So here, in this case, let me just erase this for a second. You can see that if the triceps contract, if it pulls in like this, it's going to result in pulling the arm straight like that. And that is why we call that an extensive because it extends the limb out and a flexor. It's like you flexing. Think about it that way. All right, That's all I have for this one. I'll see you guys next time.