what's up everybody so in this video we're going to be talking about muscle and motility we're going to use this guy here Arnold swatcher to help explain this topic now we know in a living organism just like me and you we have so many systems working together and when all these systems work together we can function properly and survive right for example one of our systems is our immune system that system helps us um fight infection we have another system called digestive system that helps us break down food so that we can absorb them as nutrients um now another system that we're going to learn about in this video is our muscular skeletal system now as the name implies this system is pretty much just your muscles and your skeleton okay the combination of your muscle and your skeleton now the three things in your muscular skeletal system are your bones your muscles and your joints now what is the function of our muscular skeletal system in a nutshell it's just to move around right from to to be able to have a structure so our body can go to work um pick up things move things around function right it's anything related to movement and motility that's the purpose of our muscular skeletal system in a nutshell right now first let's take a look at the actual detailed structure of our muscular skeletal system because once we understand that then understanding exactly how our muscles contract and the extra details that'll be very easy so let's start here let's take a look at this guy's arm here and look at all the structures we need to know okay it's going to be all of these so there's quite a lot but they are pretty straightforward so let's just get into it so what's this right here we're zooming into his arm here these are bones right you can see this large bone here in his upper arm and then these other two bones in his in his forearm right so his arm already has three bones okay we're we're ignoring the hand obviously now what is the purpose of bone okay so you may be like well that that's easy what do you mean you mean it's just there as a structure okay well the bone is actually pretty interesting because it's more complicated it has quite a lot of functions which you probably weren't aware of let me show you so first like you thought okay it provides a framework imagine your body without bones you'd be a blob of jelly just on the floor you wouldn't have a structure you wouldn't have a frame to be able to carry things and move around you'd just be a blob right there on the floor okay so the bone provides a framework a structure like the structure of a house now second protection of your vital organs remember your uh you have a rib cage right and inside your rib cage behind your rib cage you have a heart you have lungs now they are protected by this rib cage so when you when your when your palp punches you in the chest as a joke luckily have a rib cage there to protect your lung and your heart if that rib cage wasn't there your vital organs like your lung and your heart may be damaged okay so that's another function of our bones protection okay protection next this one is interesting most people a lot of people don't know this but the Blood your bones are is a site of blood cell synthesis so for example your red blood cells are made in your bone your bone marrow okay so that's another important function your some of your white blood cells are also made made here so very important it doesn't only have this structural purpose um and protection it also is important for actually making blood cells um and another one would be storage of minerals so in your bone you store calcium and phosphate uh which is good for keeping your bone strong and all that um and other thing um and your body also needs calcium so sometimes when your body needs some calcium it can be released from the bone okay to be used somewhere else so that's important it stores other minerals now lastly it can act as a lever this point is pretty similar to the first one of provide a framework so your bone is like a lever so when the muscle attaches to the Bone it can pull it and move it in different angles and directions to allow certain things to be able to happen so it can act as a lever and we'll look more at that later in this video so that's important notice the bone has so many functions it's not just there as a structure okay many functions now notice these bones they join here now imagine if if this was the scenario imagine it was bone on bone imagine when you move your arm pretty much you're grinding bone on bone wouldn't that mean that your bone would erode and that would cause a lot of pain and damage that's true so actually we have something here called called cartilage okay cartilage um and what this does is it's pretty much a layer on the end of the bones um that keep them smooth and is good for stability um is good for um absorbing impact and reducing friction so let me show you here okay it reduces the friction in other words makes it very slippery so it's very smooth because bone on bone would be very rough so this is very slippery material that helps reduce friction and it makes smooth movement because it's quite slippery okay so that's important we have this layer already there and you can kind of tell if you've eaten chicken before you would know at the end of the chicken leg there's like a layer and that's called like the thin thin kind of transparency layer that's the cartilage you don't really need to eat that but some people do so that's the same thing on our bones we also have this cartilage layer okay very important now the cartilage remember it's only there for protection and reducing friction it doesn't it's not like glue it doesn't connect this bone to these two bones it's just there for um reducing friction that's all so what connects the bones to each other CU right now these bones are not connected if you leave it like this they'll just fall apart so the thing that helps connect these bones to each other is something called ligaments ligaments are like little structures that physically go span from this bone over to that bone and keeps them together okay and we have a lot of those little ligaments working together keeping the whole joint stable and together okay so that's where ligament is a little structure that attaches bones to one another okay awesome so now our our joint is nice and smooth there's no friction because of the cartilage our bones are now linked together now what else are we missing can our bones move by themselves unfortunately not right we need muscle so obviously he will and this especially Arnold swatcher he has humongous muscles so the muscle is going to come here give me one second okay here we go so you can see here there's the muscle label it for you guys muscle so our muscle this is our muscle the muscle is the thing that is actually going to contract okay now imagine the muscle is just by itself will that cause any movement of your bones no your muscle needs to First attach to the bones if it's not attached the bones will not move so this part here this white part here that is attaching to the Bone here this is called a tendon so a tendon first of all let me Reve the muscle a tendon is a little structure that con that connects the muscle it's a it's from it goes from the muscle to the Bone okay that's important so you can see here we have a tendon here connecting the muscle from here to this bone and then we have two tendons up here connecting the muscle to the to the bones on top okay so that's very important so the tendon is important linking the muscle to the Bone ligaments are important because they attach bone to bone okay okay awesome so now what are we missing what are we missing we have now the muscle uh that can contract and now since it's attached by the tendon we can move the arm because when this muscle contracts it will pull here on this bone and move the arm um up so that your arm is bent right very important that's how it works but we're missing one thing we're missing one thing we're missing neuron if you don't tell your arm to move it's not going to move so you have an important structure okay called the neuron which is just another name for nerve cell and a nerve cell carries the signal from your brain where you decide to move your arm to the muscle and tells the muscle okay contract so that's what your neuron does that's very important without it we're not going to do any contraction so finally I want to show you this area here so a joint is the area where two bones meet in a joint what can we find what can we find in a joint think about it what can we see here many things so in a joint where two bones meet you can have bones that's important you can have muscle for example maybe a bit of the muscle is in this location of the joint uh cartilage right ligaments for sure tendons this tendon will be in the joint area and even nerves sometimes I didn't show in this diagram but even nerves can pass through this area for example a nerve that comes from your brain down to your to to your fingers they would need to pass through this area here so you can even find nerves here and other blood vessels like arteries and veins okay super important so that's very important we covered now let me just label this these are all the key structures you need to know for this chapter so make sure you know all of these and what they do their function so now that we know the structure of our muscular skeletal system because this is just for the arm but the concept applies all across your body all across your body okay but these are the key words you need to know now let's talk about the purpose of movement why do we need to move what's the purpose in our muscular skeletal system so many cool purposes for example you can probably think of most of them by yourself but um let's see how many you actually came up with so escaping danger okay this fish here has little wings it can literally jump out of the water and move and fly fly a little area to escape danger for example another fish trying to catch it same with me and you we have muscles to run our nuts off when someone is breaking into our house right so escaping danger is a very important function uh next one is interesting is searching for a mate for example this little guy here he swims all the way from the ocean onto the shore and waits for a mate okay and the mate will come there eventually and then they will have kids okay so just moving around to find a mate is um is important another one here finding food foraging for food for example these guys here they have to fly from flower to flower to collect the the Poland and the nectar right just like me and you I got to walk all the way to the fridge for my food right now this guy here migration some animals need to literally fly across the world like this guy here he has to fly from the Arctic to the Antarctic opposite parts of the world um because of different seasonal changes and food availability right and then one last one simply just to go to different places so not escaping danger not searching for a mate not migrating um not finding food sometimes it's just like you know I want to go to Europe I want to live there it's not because I'm migrating because of food or something just dispersal so some bats like this one here will literally just fly to different will establish different colonies in different countries not for migration purposes just because they want to disperse across the world so these are all very important functions so make sure you know you can State some functions of our muscular skeletal system so here is a nice summary because I said a lot of words a nice summary for all the reasons for why you would need Locomotion Locomotion is just movement um and I gave these specific examples here on the previous Slide the Flying Fish the honeybees and all those the examples I just gave but these are just examples obviously this applies to every animal right or every organism so you can think of some organisms and think how they would need Locomotion these are just some examples okay now we need to distinguish two key words endoskeleton and exoskeleton so me and you okay vertebrates we have an endoskeleton meaning our skeleton is located inside our body okay we we don't walk around saying a nice skeleton when you see a when you see a guy for the first time CU that's inside his body you can't see it right so an endoskeleton and Endo means inside so it kind of makes sense based off the name endoskeleton so this is bone skeleton is made up of bone is on the inside of the body so our muscles will attach on the outside of our bone like I just showed you on the um one of the previous slides right so an endoskeleton exists in vertebraes any organism with a back bone and a skeleton is called a vertebrae for example bird okay it has an endoskeleton this whale here this Orca okay this lemur this okay a lot of organisms for all of all of these they're all vertebraes and they have an endoskeleton so what's an exoskeleton okay an exoskeleton is when the skeleton is on the outside of the body now this kind of skeleton is not made up of bone it's made up of a material called chitin okay chitin or chitan and it's located on the outside of the body so the muscles will attach to the inside of their skeleton oh that's weird well don't worry we're going to see a picture just now so remember for the endoskeleton the muscles attach here on the outside okay from bone to bone to try and move us around wherever we need to do now an exoskeleton the muscles are on the inside of their skeleton which is made up of not bone but chiton let me show you so here we have a little um U insect okay and we can see if we zoom into its little leg area here you can see here we can see that this thing here is a skeleton but it's on the outside of the body okay and it's made up of chitten so it's not not on the inside you can see it I can see their skeleton from the outside unlike a human which is on the inside now their muscles notice are on the inside it's on this little skeleton is hollow okay little skeleton is hollow and the muscles are on the inside so you can see this muscle here is attached from here to here if if it contracts what happens this leg will bend whereas this muscle here if it contracts it's going to pull the leg open so it becomes straight okay so you can see the muscles are on the inside okay of the this joint of this little skeleton so these kind of things exoskeletons exist in organisms like arthopods these are like organisms basically that don't have a vertebrae or backbone or skeleton so like insects is an example okay so you can see how they're different so make sure you know the difference between endoskeleton and exoskeleton okay that's very important to understand okay so now that we've introduced the whole structure of our muscular skeletal system we need to go in a bit more detail with joints specifically okay our joints so we have so many joints in our body you can think of them think about your own body and think about where your joints are and how you can move that joint for example our shoulder if you thought about your shoulder you can realize you can kind of move your shoulder your arm in all directions and you can move it you can bring your arm forward backwards sidewards you can make a big circle this kind of joint okay where there's a um it's called a ball and socket joint because look this bone here is like a ball and this one here is like a socket it's um receiving this bone it's receiving this it's receiving the ball so they work together and when it comes together you can move this joint in all directions you can move it in three planes so if you look at this here like a ball and a socket okay so this bone here is making the ball and that bone here your scapula is making the socket okay and you can move this joint in three plane so it's very movable same with your hip your hip works the same way your femur here is going to have the the ball and then your pelvis will have the socket okay now these are ball and socket joints another kind of joints we need to learn about is hinge joint and this one you can find in your elbow or your knee have you noticed you when you try and keep your leg still and you move your knee you can only move it in one plane can you can extend it or Flex it you cannot move it side to side or make circles with it like your shoulder right so this joint is far less mobile than a ball and socker Joint so I want you to know that you have different joint types in your body the two key ones you should know is ball and socket joint an example is your shoulder and your hip they are very mobile whereas your hinge joint is not mobile it can move in one plane ex okay much less flexible okay now for example if you're me I'm very unflexible okay so my if I I cannot for the life of me do the splits okay not even close so let's think about this we call that range of motion so if I ask you if you if you have to look at your your your um joint you can consider something called range of motion meaning how far can this joint move what how how much can it extend and flex what is the extent to which it can to which this joint can move we call that range of motion if you have a high range of motion then your joint has a lot of flexibility can move in a lot of different angles if you have low range of motion it doesn't have much flexibility and it can't move that much okay so for example uh remember your bone is going to be your little lever here this is the thing that's being moved the lever your bone okay a lever is a rod or a stick or something that is rotating above um around a fixed Point The Joint here is the fixed point this part is staying still and this bone is moving relative to this fixed point this fixed point is called a fulm but in the body we call it a joint okay so you need to know these two words levers and Fulcrum now for example here you can see now this arm is flexed to about 90 degrees 90 degrees okay but its range of motion is much more it can move more this way and more that way so how can we measure range of motion okay range of motion we can measure using a gometer so for example it's a little tool here where we can measure how um to what extent The Joint can move so what you do is you make your leg straight say you're trying to measure the uh the range of motion of your leg you make your leg straight and then you take take this little tool you make the tool straight then you bend your leg as much as possible and then you move that tool you bend that tool along with it and then you can measure the angle that you that your leg is able to move okay that that way you can see your range of motion now why do we care about this so a lot of people they get injured or they will have to have a surgery around their knee or their shoulder or something and it will take time for them to recover because they have to do exercises and all those kinds of things now this tool is useful to document Improvement so maybe day one after operation your joint is very stiff and it can't move much and you measure it using this G gometer and you write down that angle that it can move then a week later you measure it again and hopefully there's some improvements so you can write that down and you can kind of measure the progress of recovery for this patient okay it's it's a not that complicated the function but it is useful okay cool that's it now um now we're going to look at a specific joint okay because you need to know this joint they can ask questions on it this one um so we need to look at it we're looking now at this gu this guy here okay we're looking at this area here his hip joint hip joint okay the hip joint is interesting okay we're trying to zoom in here you can see here um uh this is the joint okay so this here is going to be his femur his big bone here let's label some stuff so this bone here is the femur the femur is going to form the ball so this is going to be remember I I showed you on the previous slide this the hip is a ball and soccer joint okay so this is going to be the ball on the femur remember we're going to try and show you what do you think this little layer here is on the socket and this layer here I mean this layer in the socket and this layer on the ball what do we call that again cartilage right the cartilage is the little protective smooth layer to help um The Joint have a lot of less friction and absorb some impact to protect the bones right that's cartilage so by the way we're looking kind of um at a a at um um the hip joint but we cut this part off because normally this part wouldn't be able to you wouldn't be able to see this part because it's lodged inside the socket so this image here is a cross-section we cut open the joint so you can see what's going on in the inside normally it's covered normally it's deep inside the socket and you can't really see it so remember this image is not 100% realistic we have the image cut open so you can see the inside okay um great now we can see this little things here connect conc in this bone here to this bone here okay things that connect a bone to a bone is called what a ligament okay that keeps the joint stable um and connected now now the other bone here is our pelvis and you can see it forms the little socket here okay so that's the socket and the femur is the ball now one thing that we didn't mention on the other on the intro on the on this slide here that I that you should know is this in this joint okay you can see this joint here there's little fluid also circulating around here and we call that sovial fluid okay and on the next slide I'll put the definition but sovial fluid is basically a little lubricating fluid meaning lubricating means to make slippery so kind of like the cartilage which is smooth and slippery this fluid is also there and it's very smooth and slippery and it helps to um to keep the joint moving very smoothly okay so that's one function another thing you should know that can be in a joint is synovial fluid okay okay here here we have a summary of it so you can see the hip joint make sure you know this joint all the structures and we can see all their functions so uh I just want to highlight something here uh see the sovial fluid this is new for you guys a lubricating fluid within the hip joint that reduces friction okay um by the way you will see when you read this table the word connective tissue very often so so things like ligaments and tendons and cartilage they're made up of something called connective tissue so you know your fat tissue that's a kind of tissue or your muscle tissue that's a kind of tissue so these things cartilage ligaments and tendons they're made up of a kind of tissue that we call connective tissue so we have covered everything all the details we need to know about joints okay every single detail now we're going to go to muscles and look at muscles in more detail all the contractions the structures we need to know now REM what I want to highlight first is that remember we have more than one kind of muscle in our body we don't only have these skeletal muscles that we all think of the skeletal muscles you try and make big when you work out we don't only have those we also have cardiac muscle and smooth muscle because your heart needs to contract to pump blood all around your body and your intestines need to contract to move food all the way from your stomach out through your anus right so these are also muscles Contracting so we're only going to focus on the structure of skeletal or stried muscles okay bear that in mind so no we have three different kinds of muscles we're only focusing here on skeletal and stried because the other ones have a slightly different structure that we don't need to know about for this video so muscles are made up of a cell right muscle cells or muscle fibers these are synonyms they mean the same thing okay so we're focusing specifically on skeletal muscle cells as I just mentioned not cardiac or smooth muscles skeletal muscles now one thing that's pretty unique about skeletal muscle Muses is the fact that they are voluntary meaning we think about it before they contract we tell our biceps to contract we tell our toes to to contract we we tell our mouth to move okay right we control it if we if we decide not to move we won't move whereas these other two they are involuntary they are out of our control we cannot decide when they move imagine we had to decide when your when your heart pumps or when your intestines start moving food around that would be so timec consuming and we never get anything done if we had to keep thinking about this stuff because we'd be busy all the time we pretty much just die half of us would just get lost in thought and probably die because they forgot to pump their hearts right so that's important one cool thing is they're voluntary so let we look at these cells we're zooming in here and looking at a bunch of these cells we can see here we have five of these muscle cells um what's one thing that's unique about them that you probably notice that is that they're very long they are cylindrical and long in shape that's different from a lot of other cells that we know right in body um and that's very important because they should be long depending on how long your muscle is so they can move that move that limb or whatever you're trying to move so some muscle cells will be very short if they're like in your hand or in your face and and other ones would be very long if they're in your leg or on your back or something right so it depends on which body or which uh area in the body we're looking at now another thing you may have noticed is that these cells have more than one nuclei we call them multi-nucleated so why is that so because these cells are formed by the fusion of smaller cells so when smaller cells link you form these large long cylindrical muscle cells so therefore the original cells each had a nucleus so when we fuse to make this longer cell both of the nucleus will combine so you'll have more than one nucleus so sometimes it can be more than two cells you can have many nuclei on one cell not just two even more um and that's important anyways because the cell is so long if we only had one nucleus to control the entire long cell it wouldn't be so we wouldn't be able to control it so well so it's very important that we actually have more than one nuclei because that way we can control the the cell much better then the last thing you may have noticed that we should point out is these striations these lines on the muscle cells notice they're all over this is part of the reason why we call these cells sometimes stried muscle cells and not just skeletal muscle cells okay and we're going to see exactly where these striations come from so now here's our muscle cells we got to look at something you may have noticed each of the the these cylinders these muscle cells have a a bunch of pipes inside them so pipes a bunch of pipes inside this long pipe wow now these little pipes are called myof fibros and each muscle cell has many of them these little myof fibral are the things that are going to contract these are the contractile units when all of them contract then the whole muscle cell will have contracted right so these are the things actually doing the work actually Contracting let's take a look at how they look and you'll be like wow that's too much for me next video no don't worry it's not that bad we're going to point out the structures and we're going to slowly talk about how contraction works so let's label some things first look you should when you first look at this you'll notice it's just a pattern look we got one we got the Ziggy zaggy line here Ziggy zaggy line here that's one unit then we've got another unit then we've got another unit so it's just a repetition of little units what do we call these little units sarir what do we call these little um from one of these squiggly lines to another one of these squiggly lines that's one sarcomere so these squiggly lines we call Z lines and I like to remember it because it's like Ziggy zaggy these lines look they're like like Z's okay now in the middle there's a little structure here going vertically like this this dark structure we call that the mline and I just like to remember it as the middle line because it's in the middle of this sarum here okay then we've got this horizontal thing here which we call myosin it's known as the thick filament because it's thick it's a thick protein okay um and then there's one ad adjacent to it this thinner one which I Illustrated here this picture is actin it is thinner so we know it we know it as the Thin filament both of these are made up of protein so myosin this thing here remember proteins are coded for by our DNA and DNA will code for a certain sequence of amino acids and that that sequence of amino acids will correspond to a specific protein so this re is just a protein a kind of protein and the actin is just a kind of protein okay now let's label some more things so notice the region from where these two overlap you can see they overlap from here all the way to here we call this area the dark band going to give you another name as well it's called the dark band because these two areas overlap so on a microscope because they overlap this area is thicker look this whole area is thicker there's a lot of in this whole area there's a lot of proteins going on a lot of overlap and all that so this area on a microscope will appear thick and dark that's what these Tri are isn't it crazy if you look at these muscle cells these little dark areas every now and then that's just these dark bands these overlap of all these filaments okay um and we can call them the real way we call them is um a band uh but you guys don't need to know that it's not in your book so I'm just putting it here so in case you see it somewhere when you when you watch another video or you are studying or something you see a band this is just the dark band it's another way of saying dark band it's a good way to remember because you just think dark and you'll see the next part here where there's no overlap right so here this is called the light band okay another way of calling it is iband but again you don't need to know that okay don't need to know the I band just be aware if you see it what it is okay so that's where the light areas are okay so that's cool now you already know why the stations exist because of these dark and light bands this dark line uh this dark band caused by this overlap of all these filaments and light band when there's only acting filaments okay and last one which you don't need to know I'm just going to label it because it has a name is this area here in the center that's called the H Zone but don't worry about it okay so let's quickly finalize this just going to make it clear so this area here where we have the overlap of these filaments called Dark band and this other area here is light band now when the muscle contracts right something will happen here and the the sizes of these dark bands and light bands will change so they they're not always constant so depending on if the muscle is Contracting or not the sizes of these Tri will change okay now there's one other structure we need to point out before we move on so we're just zooming into one of these things here so from from here I added one yellow structure here which you need to know so don't get confused here from this Z line here to this Z line that's one what that's one sarcom we still got the myosin we still got the actin we still got the mline the only thing we added here is this thing that connects the myosin to these to the Z line this yellow one this yellow orangey line right these are called Titan fibers okay and this is also made up of protein so bear in mind the actin is a protein myosin is a protein protein Titan's a protein whole lot of protein okay so this Titan is connecting these myosin fibers to the zline and we're going to look at all the purposes of this Titan fiber later in this video for now just know the structure the whole purpose of this slide is just structural make sure you know what to label and where what is but don't worry about any function yet we're going to talk about that now okay now let's talk about so we know now the structure of our muscle we know now these little myof fibral are the units that are Contracting and many of the myof fibral make up one muscle fiber and when they all contract this muscle will contract now how exactly does contraction happens well I told you it starts off with your brain right we can control these muscles so our brain is going to send a little cell out which we call a motor neuron or a nerve cell okay and it's called motor because this is the kind of we have many kinds of nerve cells in our body now the nerve cells that are that are sent out to cause muscles to contract they are called motor neurons or motor nerves Okay so uh here's one we're going to call this one a okay it's just a random um way of naming it okay there's not actually a nerve in your body called motor neuron a we just naming it like this for this picture here we got muron a there's another here we just going to call it B okay so how exactly does this thing work so you're going to send a signal from your brain all the way to the end of this little motor neuron where it connects with the muscle okay so we're zooming into this area here where the nerve connects with the muscle this ending here of the nerve we call it the terminal end okay so this is the the name we give this the end of this nerve is called the terminal end which is weird because terminal means end and end means end just means end end at the end of the day um and now this here okay is going to release a signal okay which is called a neurotransmitter so when you think you send this the signal all the way down and it gets released here as a neurotransmitter okay a neurotransmitter go put it here now the specific kind of neurotransmitter because you have so many kinds now the specific kind of neurotransmitter that's released between a nerve and a muscle um or skeletal muscle is called acetylcholine okay so acetylcholine is a kind of neurotransmitter that that is released from the terminal end and will travel across here across this neuromuscular Junction so we call this area here the zoom in that I made here the neuromuscular Junction makes sense because neuro means nerve and muscle is muscle and muscular means muscle so this Junction here is the junction between the nerve the neuro and the muscle so neuromuscular Junction so this terminal end will release this acetal Coline or this neurotransmitter and it will travel all the way to the muscle where it will tell it to to contract okay and you may be like okay how does this neurotransmitter tell it to contract we're going to look a little bit into that but not much detail because you guys don't need to know much detail okay so what happens is this nerve signal this neurotransmitter comes across and what it does is this normally so here we have I simplified this diagram because right we were looking at this before a lot of of these repeating units we're only now looking at one unit because if you understand one unit and how one unit contracts then all of them do the same thing so if you understand one you understand all of them and they all work together like that to contract so we're only looking at one here one sarom here now what happens is this nerve sing signal will be sent and this neurotransmitter will be released and this neurotransmitter acetylcholine will basically trigger the muscle cell to release calcium from the muscle cell okay so there's there's calcium stored inside the muscle cell and it'll be set free and this calcium has a job normally these actin filaments right these ones here these thin filaments they are covered by something they're like covered prevented from doing anything they're like held held away okay now this calcium is going to come in and remove these things these obstructions because normally these little myosins they have these little structures called myosin heads and they're like little hands and what they want to do is they want to grab onto this actin and Pull It in like this to contract it you see they want to pull it in so this muscle can contract but as long as they're covered by these little things then they can't grab on they're like obstructed to prevented from doing so so the signal what the neuron is really doing is it's sending this acetylcholine and this acetylcholine is triggering the muscle cell to release calcium and calcium is going to come and remove these little obstructions okay now it's interesting wait a second can't seem to click on that there it's interesting because your book doesn't um tell you guys this okay they only tell you your nerve U will stimulate your muscle to contract but I'm like how does that make any sense you guys want to know how exactly so if you want um don't worry too much about this detail that I wrote here if you know this year it's enough this will be more than enough for you guys to understand it so I know some of you will be like I don't get how the nerve causes it to contract so this is how Okay the nerve causes acetyl coldine to be released acetyl coldine will will stimulate calcium release and inside the muscle the calcium will go and remove these things now that now that the actin filaments are exposed and free now these myosins can bind to this actin and drag it and Pull It in Pull It in you see and by pulling it in now the muscle is Contracting okay the muscle Contracting so that's really what's happening during contraction okay the actin filaments these here are sliding over these myosin filaments these myosin filaments are the ones pulling these actin filaments across okay this results in the sarcomere shortening because originally look originally the sarcomere was very long right look very very long now after contraction it's very very short okay so that's the basics we call this the sliding filament theory because these are filaments and they're sliding over each other that's how muscles contract we're going to look exactly how this myosin heads is pulling these actin like the mechanism of how it works but if you understand this basic idea of how contraction works that's already a very good start so now you're going now we can learn the details of it next okay so and again in summary so to compare this here so in relaxed form if we have two of these sarir we're looking at them then the sarcom will be very wide you can see when they contract now these sarcom ears are much shorter much shorter now remember this dark band here this dark band here is the where where it overlaps where the um the dark the thick filament and the thin filament overlaps so when you contract what's happening is the dark band or we also call the a band will stay the same width notice you can see right so the dark band doesn't actually decrease in size but the light band because these actin filaments are sliding across now this area where the actin is alone is going to get less so we can see the light band is actually getting shorter okay and the H zone is also going to get shorter but don't worry too much about the H Zone I don't want you guys to worry about that one I want you to understand that the dark band stays the same regardless of contraction but the light band will get shorter you can see so clearly from this image so let's go over the key points so during contraction the filaments the thick and thin filaments they do not change in length look the actin is staying the same length the myosin is staying the same length they're not getting shorter or longer okay because they're sliding past each other they're not getting shorter or changing size okay very important to understand that during contraction the sarcomere gets shorter from being from this Z line to this Z line now it's from this Z line to this Z line so it's much shorter during contraction myosin filament stays still and actin moves so remember during contraction this myosin is staying in one spot it's going here and grabbing and pulling this actin over it making it slide over it but itself is staying in one spot the Acton though is actually sliding and moving okay so the Acton is moving okay so again during contraction the dark band will stay the same the a band and then the light band will be shorter and then the H Zone will get shorter but again don't worry about the H Zone okay so now we know how the contraction looks like how these myofibrils contract and get shorter and makes the muscle contract right but we need to know now the mechanism because I told you these myosin heads are going to grab these these actin and pull them across like sleeve okay so this so that this sarcomere gets shorter and the myof fibral is contracted now how exactly does that work we need to know the details here okay so we're going to look now at details the this microscopic level of it okay okay so it starts here we have our zline it's a very um zoomed in diagram we have our actin here so that's the thin filament and we have our myosin the thick filaments and here is the myosin head okay so we're pretty much don't want to confuse you guys we're just looking at an zoom in area here okay how it looks like okay so what happens is this myosin heads okay they have ATP on them ATP is going to split into ADP and P because remember ATP is a Denison triphosphate so there's three phosphates now it's going to split into ADP so D phosphat so two phosphates and the other alone phosphate once this happens this causes the myosin heads to like um um rotate and move okay like kind of like loading a gun okay I like to think of it as loading a gun so it's going to move because it wants to grab onto a specific area Okay so once it's moved so once this ATP split into ADP and P this myosin head will um will kind of change position like this you can see from this diagram then this p is going to leave when this P leaves that causes this myosin heads to grab on to the actin okay so now it's going to grab on it's like taking off a glove now that the glove is taken off now it can grab grab onto this to this actin okay so it attaches to this exposed binding SES on actin okay we call this when these when these um um myosin heads binds onto actin we call that cross Bridges we're forming these cross Bridges that's just when these myosin heads bind to the actin that's called cross Bridges okay so you can see now now it's grabbed onto here now what's going to happen is something interesting now the ADP which is still there is GNA leave when the ADP leaves that means that this fos that this um myosin head has to return to its original position because ATP um splitting into a DP and P cause it to be here but as soon as ad DP leaves now it will return to its original position but because it's attached to actin it's going to drag on it so it's going to kind of pull on this actin as it's returning to its original position we call that pulling of it pulling of this actin the power stroke okay this power stroke so it's so what's happening is essentially this let me show you it's grabbing and now it's pulling to the inside Contracting the muscle okay now remember it now it did the power stroke but it's still attached it's still attached now it it will it will do this power stroke and now it will end up here um still attached when ATP binds now it will de um um stop being attached it will detach like this so remember when it's doing the power stroke at that point it is still attached if we want it to contract again it first needs to detach so that it can grab onto another spot further down the line okay because now it pulled it's like when you pull a rope you pull it close to you and then you to and then you need to let go and grab a further part on the Rope so you can pull again it's the same thing here when this myosin head pulls and does the power stroke now it pulled the actin but now it needs to um detach so it can attach again on a further side and pull some more okay so that's very important so after doing the power stroke another ATP will come in and bind to it so that it detaches and then that ATP then the cycle will repeat then the ATP will split into a DP and P and that will cause its position change to grab along in a further spot and so on so that's the contraction cycle so I want to highlight again here remember without your nerve sign signal this actin will be covered with a bunch of stuff this myosin head won't be able to grab onto it but with your nerve signal you cause calcium to be released okay in the muscle cell when calcium is released in the muscle cell these actin will be naked this calcium helps remove all this other nonsense to make actin free so that these meos and heads can bind to it so as long as calcium is high so as long as you're sending a signal with your brain Um this can happen but if you don't send a signal and if calcium is not high inside the muscle cell then this can't happen because he these actin filaments will be covered okay and also you need ATP um because ATP allows it to be detached so so that it can grab onto a further spot and pull some more so if you don't have ATP um it won't be able to um continue okay so here is a nice summary of starting from the neuron all the way to contraction you can I hope you can remember all these steps at least all the key words and be able to write out all the keywords and then you should be great for describing muscle contraction okay so remember how I just said you need ATP so why do you need ATP think about it when you contract okay when you're Contracting um your these myosin heads will still be attached and to to initiate a new contraction ATP has to bind so that this myosin heads can detach from the actin so that it can attach to another spot and pull again if you do not not have ATP so for example when you die your body is dead so you're not making any more ATP your cells are not alive right that means you have no ATP so your muscles these myosin heads will remain stuck on the actin because ATP is required to make them let go so because of that you undergo a state of rigor mortise you'll notice when something died it is very stiff when you try and open something's hand or something when when a person dies with their hand closed you won't be able to open their hand because they um their muscles are stuck they physically um these myosin heads can't let go without ATP so therefore this is called rigor Morse when you cannot when um when something is very rigid the muscles are very rigid and you can't open something's hands or you can't move the dead person around you can't move their joints freely they're in rigor mortise and it will remain like this for nearly two days um because after around two days like 36 hours um these proteins all start breaking down and all this everything starts falling apart then then you'll be able to move the person freely again because everything is broke everything fell apart it degraded over time degenerated over time okay cool we covered all the hard stuff now this is the last couple key words we need to know the first one here is antagonistic muscle pairs so um when muscles have the opposite opposite function we call them antagonistic muscle pairs for example if we use our biceps we know our biceps is going to contract our forearm up so it's flexed right when you lift up a dumbbell and your triceps will will do the opposite it will straighten your arm so biceps break break eye and triceps bre break eye they are antagonist muscle pairs they have the opposite function the same with your lungs the book really wants you to know this it's another example of an antagonistic muscle pair it's a bit more confusing but you need to know it's in the book okay they specifically want you to to know these two the muscle the biceps and triceps and now these two um so you know um to inhale you have a spe specific muscle like we know you have your diaphragm which has a very important role but we're only we're only going to care about these two for this example you you have a little muscle which attaches um in an upwards angle from the front Okay it's called your external inter Coastal muscles and it is in between your ribs so you can see it's this one here it attaches from here in that angle upwards so kind of like this man here pulling this rope so when this guy pulls this rope what is going to happen to the rib cage it's going to kind of go like this if you look at the rib cage here it's going to kind of raise up right because if you're pulling this way like this guy is you're raising the rib cage by raising the rib cage we increase the capacity for air so that you can inhale right so this muscle here the external inter Coastal muscle will allow you to inhale okay it will raise your rib cage so that more space for air to come in the other one that is that is behind the external inter Coastal muscle so we called the internal inter Coastal muscle so yeah really the reason why we call the external inter Coastal muscle is because it's on the most outer it's more outer than the internal one the internal one is even deeper so the internal inter coal muscle runs the opposite way downward Wards so you can imagine if this guy is hanging here it's going to pull the rib cage down to kind of go from being open and a lot of space to having very little space so the internal inter coal muscle does the opposite thing it's going to make the rib cage smaller to force air out so these two are also examples of antagonistic muscle pairs so I hope this um kind of diagram makes it clear on how they have the exact opposite function with X with inhalation and exhalation okay now we're almost there guys we coming now to Titan remember I showed you on one of the other slides Titan so Titan remember how I told you it's attached it um links myosin fibers to these actin fibers right look you can see now what is the purpose of Titan okay it's really actually pretty interesting I want you to think about Titan like a little spring okay like a little spring it'll make a lot of sense if you think about it like that okay so when sarir shorten during contraction okay what does that mean again so when these things look when they contract and they come in the sarir are shortening right they're Contracting they come in the Shamir shorten guess what's happening okay this will create a spring like tension in Titan so imagine have you ever had a spring and you compressed it down like that into this kind of shape when you let go it's going to shoot back out into its original position right it's the same thing with Titan it's like a spring so when the muscle contracts like this it makes this this uh this Titan the spring like tension it makes it be like this so that after you contract and you want to relax again this Titan will kind of help um push this actin back so that you can um stop Contracting okay so Titan is very good for that reason okay uh it creates a spring-- like tension in Titan that is released when the muscle relaxes so in essence Titan helps to recoil the muscle back to its original shape okay so after you contracted the Titan will be like a spring and when you relax it will help push your muscles help push your muscles back into their um normal position okay so by doing that this allows each sarcomere of the muscle to reset and be able to contract again right okay another thing that it can do is this the opposite so if we think about the opposite way say say this right here is your biceps okay now let's say the antagonistic muscle pair is Contracting when the triceps contract think of what's happening when your triceps are Contracting you're stretching out your biceps okay you're because you're making your arm straight so now this muscle is being stretched out okay so let's see so let's say this muscle is being stretched out now remember it's like a spring this Titan is like a spring so now we can assume this spring if you pull the spring apart and you let go it's going to come back to the original shape the same here so when you stretch out this muscle this Titan is doing two things it's preventing this muscle from over stretching and breaking apart and it's also going to help recoil oil back to the original shape so after after this when you want to return your muscle to original shape this little spring will help pull these back so that you can redo um so you can be reset to normal position okay because think about it if you're pulling these if these are being stretched very far there's no way for these myosin heads to grab onto this actin it's very far away so it's very important that this Titan can recoil and bring it back to around here where these myosin heads can grab on to the actin again and contract and cause contraction to happen so very important Titan's role as recoil like a spring is very important in muscle contraction okay and it's also important to prevent over stretching so make sure you know these roles of Titan just think of a spring and it will make a lot of sense okay now the last part here which will be very relatively quick is adaptations so you the book wants you to learn about certain kinds of organisms I want you to know about the two categories sessile organisms and motile organ organisms um we're going to go relatively quick over this because it's it's really not that complicated so a sessile organism is any kind of organism that can move um but they don't move from place to place so in other words plants can't run around and move everywhere but they can still move so they can still for example um respond to environment so for example a flower can grow towards the sun that's movement but it's not necessarily moving from point A to point B so that's a sessile organism okay whereas a motile organism is one that um they have adaptations that allows them to move within their habitat okay like me and you we can move around okay so let's look at this example of a cile organism the Venus fly trap so this organism um it typically surv um lives in in in soil that is very mineral deficient meaning they lack a lot of minerals so because of the fact that the soil lacks a lot of minerals this plant needs to eat certain organisms to obtain those minerals such as nitrogen therefore they are adapted let me show you they're adapted they have these little hairs on their leaves that can trigger that can that can tell when something has entered and when they can tell something has entered this thing will just close and keep this organism in there and digest it and break it apart for the nutrients that it's missing the minerals right because the the soil doesn't have much minerals so they need to get these minerals from other organisms okay um remember don't think that these things um only only eat organisms they are plants so they also do photosynthesis and photosynthesis is still their main mode of nutrition they only eat organisms every now and then because of the slight lack of minerals in the soil but they're still largely mostly dependent on photosynthesis okay so that's an example of a c sessile organism I want you guys to know about let's look at a motile organism it's interesting um we're going to look at probably the slowest motile organism which is the sloth you know how fast they move it's actually crazy they it takes them 4 hours to complete 1 kilm or even worse 24 minutes for 100 m you know when sometimes in P you have to do the 100 meters and you do it in like if if you're pretty fast you can do it probably like 12 seconds or something but if you're slow like me you're probably around 15 16 seconds um U around there now these guys are no match for you they take 24 minutes to do one 100 meters so that's crazy right so motile but they're pretty slow now what's interesting about them is when they eat food like a leaf it takes them a month to process it and they only poop once a week but every time they poop they they poo around a third of their body mass that's like you pooing 20 kilograms 20 or 30 kilograms it's crazy at once so these although they're weird I think they're pretty weird they're pretty interesting so they are typically found in trees so their body is adapted to move more in trees so they're not very good at moving on land that's why they move so slow but they're they're much better than me and you at moving around in trees because they have very good grip and and very good at pulling themselves to higher locations okay so that's what makes them adapted for it okay so make sure you know the difference between a sessile organism and a motile organism and then um and just some key feat some key descriptions about these two in case you're asked about it okay and then last thing we're doing here is swimming adaptation so we're going to look here at a dolphin and look about how this thing is adapted to swimming better than we are okay what makes them so good at swimming how are they adapted to be motile and move around in their specific environment because me and you we're adapted to moving around in our environment where there's no water there's land it's very easy to move how are these guys adapted to their environment let's look here so first of all their body is very streamlined they're very they don't they don't have much viscosity of the water they kind of just let like throwing a needle into water they they they the water doesn't slow them down much because the way their body is shaped okay they have no body hair so they're very smooth and hair provides resistance so if they have no hair that makes them smoother and reduces their drag in the water they have no legs and if you if you have tried to swim legs are not that good at swimming right so it'd be great if we had a fin so they have this fluke tail you call this fin in the back we call it a fluke tail and this one is adapted it's very strong and it moves up and down to help them swim very fast much better than than legs right um here they have this little hole here called the blow hole this is where they pretty much do gas exchange it allows air to come in and air to come out when they rise to the surface and when they're underwater this hole closes so that water doesn't leak into into their into their lungs or their body okay so they have this blow hole which is pretty unique that's pretty useful for swimming because it means they can kind of be underwater um longer because it allows gas exchange to happen without their face actually being out of the water um and unlike us they can stay under under water for quite several minutes at a time right me and you we go underwat and we're swimming we really struggle even for 30 seconds or a minute right they can stay underwat for much longer okay and they also have flippers in the front which helps them change direction and steering okay and lastly a long actually what's interesting is these actually long time ago um before Evolution was really like long time ago in evolution these used to be land animals and over time they adapted with Evolution and became ocean animals which is why they're actually me alien so they have many characteristics like me and you such as milk production um um um and many other things that make them similar to us because they used to come uh evolve from the same organism that me and you evolve from they just happen to get adapted to the ocean um whereas we got adapted to other things slowly okay so just know some of these adaptations that makes an organism good for moving and being motile in water um just a few of these would be very good um so now that's it let's just get into some questions so what is indicated by letters X Y and Z so we know here um this is a pretty simplified diagram we know this one here the thin one here is going to be our what the Y so Y is the actin filaments the thin filaments so it can be either b or d at this point we know X this Zone represents the dark band the dark band where all the overlapping is happening so it's going to be actin dark band so it's probably going to be D let's just confirm Z so Z here is the dark filament which we call myosin so it's going to be D so that's why it's important to be able to recognize these kind of structures so what is the main role of nerves in human movement to cause muscles to stretch no nerves are going to stimulate muscles to contract to move joints no it's not not supposed to move your joint it's supposed to move your bones around right so that you can move to transform pain signals no nerves um um there are kinds of nerves that can trans transmit pain signals but it's not the same ones that cause movement okay remember how I showed you when we looked at I want to find this it's important remember how I told you these are motor neurons because they cause muscle movement there are other neurons called Sensory neurons and they go the opposite way from here to the brain to tell you if you're in pain or not so it's important the ones in human movement would not be C because that would not be involved in movement that's for sensation so it's going to be D what is the difference between movement of the knee joint and the hip joint remember the knee joint was a hinge joint a hinge joint is like a door joint so Jo a door can move back and forth when you open it and the hip joint was the uh ball socket and ball joint and that has way more movement okay so the knee only allows flexion whereas the hip allows flexion and extension that's not true the knee joint can do flexion and extension and the hip can also do flexion and extension but the hip can do other movements as well the knee allows more rotation no the knee is less flexible than the hip remember the knee is only flexible in one plane whereas the hip is flexible in three planes so knee used in Walking forwards and hip is used for running around corners no that's not true they're both used for both so knee allows movement in one plane and the hip allows movement in three planes so the answer is going to be D what is the function of sovial fluid in the elbow joint it removes the waste products from surrounding tissue no it doesn't it provides glucose and oxygen to the cartilage no it lubricates the joints and prevents friction yeah it's going to be C what is the role of ligaments in humans remember ligaments connect bone to bone so it's going to be linking bones together a joint it's going to be a why not B prevent friction at a joint they don't do that that's cartilage or synovial fluid they can prevent friction Contracting to move a joint that's a muscle not a ligament attaching muscles to bones that' be a tendon not a ligament so it's going to be a