hello and welcome to part one of chapter 16 on the musculoskeletal system in this part uh we will Super simplify the muscular skeletal system we'll uh in a moment let's just take a look at the functions of the skeleton side of things and then we'll look at the function of the muscle side of things all right so the function of the skeleton in its simplest terms is is support um support for our internal organs for example and protection of our internal organs protection of uh the central nervous system um protection of the heart and support gives us the the framework um of this chest so we can create a vacuum so we can breathe in and out okay the skeleton also provides us a bunch of levers that we can use in order to move the body around and grab things and bring them towards us or push them away um the skeleton the bones also provide us with a place to put minerals notably calcium phosphorus and magnesium are the big three that get stored in the skeletal system primarily calcium of course and then the other trick that we do in the skeletal system is we make all of our blood cells um in the bone marrow so the red blood cells the white blood cells and the platelets all get produced inside the marrow cavities inside the skeletal system okay now let's turn our attention to the skeletal muscles um like the skeleton itself they provide support and protection support um those are the bits of us that help us maintain our posture just and I don't mean like shoulders back I mean just like sit staying upright um even when we're not moving the skeletal muscles are engaged um and if if you doubt that just think about how you know when somebody loses Consciousness and these slumps they they lose that ability to kind of hold position um actively using their skeletal muscles when I say protection think about you know the four layers of muscles that you have in the abdomen I mean here in the thorax we have the the Bony protection for these internal organs but in the abdomen we we have four layers of muscle that are helping us uh protect those organs and then movement uh the skeletal muscle is those are the organs that allow us to move the skeleton around and move our body in Space the skeletal muscles also provide stability to the joints as we were saying before in maintaining posture um we hold a position um we also keep the joints in place even when we're not moving um the the muscles provide stability and then finally this is largely where a lot of our heat comes from um when we're moving around um the the chemical reactions that are required to power skeletal muscle movement um is what generates heat also um if you've ever been super chilled or you've seen a patient get very very cold you know they start to shiver um that's the this uncoordinated um contraction of skeletal muscles so not like standing up and sitting down but the whole body is shaking um because the skeletal muscle is Contracting as a way of generating Heap and helping the body to to come back into the normal range you know return to homeostasis all right so that's the uh super generalized function of the musculoskeletal system I'm going to remind you of some stuff that you probably studied a hundred years ago when you studied uh anatomy and physiology um so we're going to review histology because I want to talk to you about three main tissues that make up the skeletal the muscular skeletal system U but in order to kind of appreciate how they fit together it's easier to see like let's let's review from the beginning there's four main categories of tissues there's epithelial tissues these are the coverings um the cells are right next to each other on the skin and the mucous membranes they line all the cavities those are epithelial tissues then we come to connective tissues which is not a very helpful name what connective tissues all have in common is that there are some living cells but there's a whole lot of non-living stuff that's also involved often stuff that's made by the cells um but there's plenty of this non-living stuff and then the next two categories are very easy muscle tissue it's pretty clear and nervous tissue the stuff that makes up the nervous system okay so let's take a closer look at connective tissues that's the biggest category of all of this two of the main groupings of tissues and connective tissues are are largely what makes up the skeleton bone and some cartilage um what else is in here is blood because it's got some cells but then it's got a lot of liquid in between um and then the connective tissue proper it's not such a great name but um what I want to draw your attention to is dense connective tissues these are uh things that make up the ligaments and the tendons and we'll be talking about those as well um but bone and cartilage are two big ones and then when it comes to muscle the muscle that we're interested in here is skeletal muscle all right so we're going to do bone first then cartilage then skeletal muscle so let's take a look at bone um as I said it's a connective tissue so there are some living cells but then there's a whole lot of non-living stuff so the living cells the Osteo cells the bone cells uh in the younger version of them they're called osteoblasts This is for building muscle or sorry this is for building uh bone tissue they put down the Matrix for the bone um they help to put in the calcium phosphate um and if they become surrounded by bony tissue then they mature into osteos sites and their job there is just to maintain the bone tissue and when I say surrounded I mean if they end up in here um and they're just surrounded by the Bony tissue then they just kind of maintain what's there if they're still on the outside then their job is more active they're more um engaged in putting down bony Matrix you can think of these as putting deposits in the bank account putting down some collagen putting down some calcium phosphate then we have some cells that play kind of the opposite role these are osteoclasts they're modified monocytes they actually come from the blood cells uh so just like monocytes can mature into macras in the tissues um monocytes can also mature into osteoclasts and a a bunch of them fuse together and you get this big monster cell with lots of nuclei um it's kind of an interesting thing um it its job is to break down the Bony Matrix and that sounds insane you know you just put all this energy into putting it down why on Earth would you be like destroying it on purpose and think of it as these are withdrawals from your bank account your calcium bank account you know when calcium levels are low I need to withdraw some and then later you know after calcium has been consumed it needs to be put down then the osteoblast can help put that back down um but between the osteoblast and the osteoclast we maintain a fairly Dynamic uh relationship here so the um we are continuously bringing in calcium phosphate um and uh like putting it into the bone and then later when need it back take it back out again okay so the uh people talk about this you know there's continual renewal of the bone tissue because of this kind of back and forth all right so those are the living cells then the non-living stuff because it's a connective tissue it has a lot of non-living stuff um we have the organic extracellular Matrix so organic means these are carbon based molecules and that's largely collagen it's a protein it's got some flexibility so that's the framework and then on top of that collagen framework we start putting in the inorganic minerals U mainly calcium phosphate but there's magnesium in there too and that's what hardens the bones and provides the strength of the bones and as I mentioned this is under continual remodeling bones are not impossible to break so as we'll talk about there are some fractures and there's a process for healing those fractures um because bone has this fantastic U blood supply just insanely good vasculature I mean just think about it this is where we make our blood cells there's got to be a lot of in and out of the bone um the bone actually heals really really well because we can provide nutrients we can provide oxygen and we can take away waste you know debris um in case this is baffling to you as it was to me as a student um think about it this way when you're first making the bones they're not real hard um and the best analogy I can give you for this is when you watch construction on a house you know that at the end you're going to have you know some hard walls and you're going to have you know electrical and you're going to have plumbing and you don't put the walls up first you put in the plumbing you put a framework up first and then you put in plumbing and electrical you know so blood supply and nervous Supply nervous cells um then you put the hard stuff in that's mineralize things okay so that's bones next we're going to the cartilage uh this diagram is actually from a different book I just I I kind of liked it showed all the cartilage all over the body including in the Brony um but really for our purposes right now we're focused on this side of things um we have cartilage that helps join bones to each other we have cartilage at the ends of the bones and the joints um and some of the movable joints like in the knees for example but also the things like this the pubic symphysis right here um and well all the joints um the cells are named similarly there's condr blasts and condr sites there's no such thing as a condr clast because there's no need to be taking minerals there's no minerals here in the condra in the cartilage um there's a lot of this non-living extracellular Matrix unlike the bone cartilage is terrible has a terrible but blood supply because part of what uh cartilage is about is a sponginess and and um the Matrix is H how can I describe it other than it it looks kind of glassy um and to have this kind of spongy characteristic it it does not have blood vessels flowing through it so cartilage depends on diffusion of nutrients from the outside uh connective tissue in through the the the non-living stuff um but they're you don't have blood vessels going through the cartilage this is we say um cartilage is relatively inactive metabolically compared with bone and it's terrible at healing itself um you'll know this from you know people who have uh problems with their menises in their in their knees their menis yeah plural of meniscus um they have there's there's poor healing of cartilage because of the poor vasculature takes a long time to heal okay moving on uh muscle tissue again we're talking about skeletal muscle um and this unlike the connective tissue that has all this non-living stuff around it it's mostly cells it's just muscle cells and muscle cells um like all muscle cells uh skeletal muscle cells have one trick all they can do is get shorter they can contract it's a remember the actin and the mein and the the kept from binding to each other when the tropomyosin is wrapped around and the troponin has to bind the calcium to roll it out of the way all of that stuff is happening in these cells so they and all I can all they can do is get shorter they can contract and they don't know when to do it so that we have to tell them to do it the nervous system has to tell them and it's the somatic part of the nervous system the the part that's under our conscious control so there's a rich nerve Supply every muscle has a nerve going to it one or more nerves going to it and a great vasculature um this is a an energetically very demanding tissue um it needs a lot of of nutrients and it needs a lot of oxygen so very good blood supply and then how the muscle tissue is attached to the bones is using that dense connective tissue um the the part that that connects U muscle to bone is called tendons if it's just bone to Bone it's called a ligament but it's similar tissue it's dense connective tissue like cartilage dense connective tissue has poor vasculature so tendon tears and ligament tears take a very long time to heal they they don't repair as well as bone and muscle do um we've talked about some of this this is just a cute little diagram from our textbook um the osteoblasts are these cells out here on the outside of the bone if they get caught and they end up kind of surrounded by bony Matrix um then they mature into these osteocytes in the case of a fracture when some of these osteocytes get exposed they can actually revert back to being osteoblasts and the way I tell my anatomy and physiology students about this is um so uh if you think of young parents they've got these little kids and then they grow up the kids grow up and then they just kind of help maintain um but then the the young kids have their own kids and they're taking care of the kids and the grandparents just kind of yeah I help maintain but I don't do any of the heart lifting anymore unless something were to happen something happens to the parents then guess what it's the grandparents who take over the duties of caring for the little ones and like that with bone um the osteocytes maintain mature bone tissue unless there's damage and you have to fix it in which case the osteocytes can revert to this kind of osteoblast uh um situation where they start putting down Matrix new Matrix okay and then the osteoclasts these are the ones that um were modified monocytes and multiple ones fused together that's what they're showing here is multiple nuclei and these kind of break down or dissolve the The Matrix um to put the calcium back into the bloodstream all right um and so between osteoblast and Osteo class we get slow renewal of bone it's really just about like release the calcium and then I have more calcium I need to put back down and I have to store this somewhere so let's talk about some things that can go wrong uh fractures or what we call uh when there's mechanical injury to a bone there's a ton of terminology related to this I'm not going to read this whole slide um I tried to to to put in what I had here was just a list of terms and so I tried to break it up a little bit um so what these two terms refers to is whether the physical barrier has been broken open and the bone has been exposed to the outside so if the bone uh communicates with the air through the skin or the mucous membrane we call this an open fracture and the big risk here is getting an infection the most common infection because we've got it all over our skin is stafilic cacus orius um if if this you know the staff orius gets into um the into the bone um it's a much more serious problem let me just mention in passing staf La cacus orius there are many strains that are you know they're just on our skin they're not horrible um but this is the species that there are some methylin resistant strains of so methylin resistant stacus arus that's MSA or Mera so this can be a nightmare um if you get a methylin resistant strain in the bone if it's a closed fracture the skin may be broken as but you know like Road Rash or whatever but the the bone didn't break through um so it doesn't communicate with the air how many pieces of bone you end up with if it's a simple fracture there's just one place you got two pieces of bone um if there's more of a crush you get common muted um fracture multiple fragments if the brake doesn't go all the way through the par oium stays intact on one side we call that a green stick fracture um let me introduce a couple of terms here so if the bone breaks and the two ends separate from each other they're so this is a one bone and then it breaks if the two ends separate from each other we say this has been displaced and it needs to get reduced those two ends need to be brought back together that's what reduction means as a student that term used to confuse me it just means yeah the ends need to get realigned um okay and then these last few terms uh are related to maybe what caus the the problem so clearly there can be trauma you know car accid accident or something or falling out of a tree um but you can also continue stressing the bone in the same way again and again and again um in which case we can develop a stress fracture there was a case recently of a I know very little about sports U but was reading about the World Series um a pitcher ended up pitching multiple Innings um with a broken leg and and the deal is that he had a stress fracture and it had been getting more worse and worse and worse um if there's a non-injury like there's how can I say this it's not like there's any kind of blow um but just in normal everyday activity a bone breaks we call that a pathological or excuse me a pathologic fracture and it happens in the context of some other problem so maybe the bone is osteoporotic it's already weak um or there's some other problem that has led to weakening of this bone that's what we mean by pathologic fractures and then this term evulsion means that um so the you know the the muscles are attached to bones with a tendon and if the tendon's pulling and a piece of the bone comes off with the tendon we call that an evulsion there's four steps to fracture repair I'm going to put them all on one slide with a diagram from another book and then I'll walk through the way our textbook does four steps uh one hematoma formation when you break a bone guess what blood vessels break because bone great blood supply you end up with a mass of clotted blood then in the in the coming days um you start getting the formation of a so-called soft callus it's not like goopy soft it's just not as hard as a bone would be um this is the cartilagenous callus that's forming then over the course of some more weeks we start getting a bony callous formation or so-called hard callus uh I failed to point this out but there's something called spongy bone it looks like there's sponge because there's spaces in there um and then finally um the final step this bone remodeling this happens for months and months after the Break um we're removing the the spongy bone and replacing it with the compact bone where things are uh much more organized put down in in layers all right so here are the images um hematoma from the broken blood vessels then we start up like stabilizing these two ends of the bones so that um yeah you start putting down what you can put down quickly and we can start putting down a framework of cartilage faster than we can put down bone um so that's where the fibrocartilagenous callus comes from then over this the time of of more weeks we end up with this spongy bone callus that goes all the way through even if in the middle there's that opening of the where the yellow marrow would be um that's going to get replaced during the bone remodeling and we're going to walk right through those steps again hematoma formation first um we get uh inflammation remember the inflammatory response can be in um triggered by either infection or just damage to cells and this is what it means sterile inflammation so it's not an infection it's due to damage to the tissue but th those players all come in the neutrophils the macrofagos we get the mass cell Degan ulation all of that stuff um and this is going to take up to several weeks to clear up overlapping with this process we have the cartilaginous callus forming um without going into a lot of detail this is going to take another two weeks or so to form this cartilagenous callus during this time if you've ever heard of somebody not getting um Attention medical attention right away for a broken bone and then they the so-call have to break it you know rebre it to to set it this is what is needing to be re-broken because the the cartilaginous callus has started forming but the the the two ends of the bones may not be aligned properly and then the Bony callus um continues on this this goes on for about six to eight weeks depending on the health of the person um at this point um one may have a a cast removed may start bearing weight on this this is not even close to done healing but it's it's good enough um that you can uh start uh resume some activity so you don't lose all the muscle mass uh that you would if you completely um remained motionless and then finally this this final step the mo bone remodeling um this is where we're taking out the spongy bone and replacing it with this compact or lamel bone meaning in layers uh this goes on for over a year and this looks different um on an X-ray this is actually still visible this is how sometimes cases of child abuse are documented years later um because we can still see on an X-ray that a bone had been broken at one time all right some things that can go wrong with uh repair of C of fractures um if the thing does not heal uh we have disunion the two ends of the bones do not stay together um this is a yeah failure of fracture healing this is what we would call it after six months if we if if the fracture has not repaired and it's maybe due to either putting too much load on this you know healing bone or um somebody is very sick or they don't have a good blood supply to the area there can be in infection as we mentioned um there can be if the fracture involves the joint and we'll talk about damage to joints later but this traumatic arthritis can result as we've said if there is um a reduction in Mobility um the the muscles can atrophy if we have to keep the weight off of the bone for a while those those muscles that had been you being used for walking or climbing or whatever um we're going to lose some of that muscle mass and then if um the person has to stay with prolonged immobility um the it that's called muscle contracture the muscle itself is not contracted what's happening is that um we're putting down some collagen which is protein fibers that are not super super stretchy um and so we actually lose some Mobility all right going on into joints these are places where Bones come together um there are places where they some joints don't move very much we're not going to talk about those but things like you know where the ribs come together with the sternum there's a little bit of movement there uh to allow breathing for example um but we're not going to talk about them we're going to reserve our time for sovial joints this is where you have the most movement the tissues involved are cartilage there's some sovial membrane uh that add ligaments the dense connective tissue not every joint has all these complexities but there are spaces called bity and there's minis these are cartilagenous pads we'll talk about later um of course like all parts of the body these can get injured um we'll talk about strains and sprains there can be inflammation you can have uh tears of the ligament or the tendons the cartilage can degrade and they're vulnerable to um immune mediated things there's um some autoimmune disorders in which the the immune system is attacking structures of the joints uh components of sovial joints obviously there are bones there's cartilage at the ends of the bones to keep the Bones from smacking into each other um there's an articular capsule that helps contain some fluid uh sovial fluid helps to lubricate things so that the we can have movement without um the bones hitting each other sometimes there are bie there spaces I'm not going to go into that miniski um so in addition to the articular cartilage in some um joints most notably the knees there's these extra cartilagenous pads in the middle some common joint movements I'm not going to go through every single one but I do want to point out a couple of things selection is uh the sometimes people say it's closing the angle of the joint I think it's easier to think of this way show you I have two stop my share all right let me stop share for a sec there we go I set this up so I could do this quickly um flexion generally it's movement to the front so all of that is flexion the one exception to this is thing the knee it flexes backwards everything else flexes to the front this is called flexion of the shoulder and everything else flexes forward and then extension would be the opposite movement let's see I'm G to go back to share screen um oh these two terms get confused often abduction and adduction uh I think of them as abduction and a deduction so I can hear the difference even in my own head the best way I can think to to remember this is adduction a deduction you are adding it to midline you're bringing something towards midline of arms or legs and abduction abduction is moving something away so when somebody is abducted they're taken away and so the arm is abducted taken away from midline um here are the two terms that we're going to go over what happens at the ankle I don't know what genius I uh this was but they're both called a flexion one's called dorsy flexion the other one's called plantar flexion how to remember which is which if you've ever held a door with your foot that's dorsy flexion I know it's not spelled the same but that's how I remember it plantar flexion if you need to remember this one again it's stupid but it works so it's not stupid um I think about if I have to plant a garden with my toes I have to point my toes to make the hole to put the seeds in to planting plantar fle pointing my toes okay the other two terms that get mixed up are pronation and superation pronation um the way I finally came up to remember this is if I were to play professional basketball I would have to pronate my hand the other one is a little bit easier the opposite movement if I were to carry a bowl of soup I would have to supinate again not spelled the same but good enough to help me remember the rest of these I think you can figure out or can remember your own way all right joint injuries um this will be the last slide for part one uh what we call a strain is simply stretching ing over stretching the muscul tendonous unit relatively quick recovery give it a little bit of rest for a few days and things are good uh what we call a sprain there's actual physical damage to the ligament um there's been some tearing in the ligament uh they get graded um depending on how much tearing there's been without going into a huge amount of detail grades one two and three micro tears for grade one all the way up to completely uh rupturing the ligament for grade three these are going to grade three injuries are going to take a long time to heal again because it's dense connective tissue this stuff does not have a good blood supply it does not heal especially well it doesn't necessarily require uh surgical repair but it may require Surgical repair in some cases for example when we get to the knee we'll talk about that so how it's assessed is looking for joint laxity that is how much movement that's not supposed to be there are you seeing in in the joint that is the end of part one see you over in part two