so you're me you may recall from the previous video that inside of the periosteum we have osteoblasts and osteoclasts let's talk about what those tax cells actually are so in this the first cell that you're gonna be coming across is the osteogenic cell I wouldn't worry about this one too much it is the stem cell which differentiates into these guys so it's kind of like the precursor cell if you will the first cell we're gonna be worrying about is called the osteoblasts the second one at the osteo class right over here we've already studied the osteocytes in lab and remember that I said it has sided kind of a central cell body or a cell body but the central part of the cell rests inside of a lacuna or a tiny lake and then it sends out little tendrils and it's job is to maintain the surrounding bone tissue so that's called the mature bone cell the osteo site but now the osteoblasts is called um it's usually nicknamed as the bone builder it basically secretes a substance called osteoid which we will discuss next week osteo aid is secreted by the osteoblasts and it actually creates bone matrix and then the osteoblasts becomes an osteocyte it basically buries itself inside of the osteoid and becomes an osteocyte but until it gets buried it's called an osteoblasts and it continues to create to bone material so it's a bone builder the osteoclast has the opposite role as you can see it's called the bone resorbing cell we usually call this the bone destroyer or the bone eater and the osteoclast breaks down bone material what you'd think well that's very damaging and it can be and it can actually be very painful but it's a very important part of the way that bone works so keep in mind down the line we're gonna be talking about bone remodeling both purposes are very important you need the osteoblasts for bone building but you also need the osteo class to remove bone material that is not needed in that region both both of these are very important for that so remember osteoblasts bone builders osteo class bone destroyers and the all three of these are living cells osteoblasts osteocytes and osteoclasts are all living cells the osteoblasts and osteoclasts tend to live inside of this guy here the periosteum so that's where you're gonna find the most bone matrix being added on or taken off which makes sense it's happening sort of at the outside of the bone so I would suggest that there will be one question on the test that will talk about projections and depressions and openings and these are all called bone markings so Table six point one is going to show you bone markings you don't have to get to know each and every one of them but basically I want you to know one or the other like you want to you want to know an example of one and you want to know an example of the other one now projections are things that kind of pooch out and stick out of bones and these are not accidental there's a reason why they're all there as strange as they look they're usually attachment points or projections that help to buoyant bones actually fit together better or places where muscles attach and they've created stress and they've actually created a tug on the bone and it's actually started to grow out in that region so examples of these you can you can take a look at the line ones that we'll discuss here are the trochanter zhh these are attachment points for muscles for example or the heads that help to fit into other bones this is a actually this one right here is the head of the femur and it fits into this little guy here which is called the acetabulum of the pelvic bone so this is a projection this guy is a depression so in the next so we have a few more projections here and then there's also some depressions and openings depressions and openings will be places where for example two bones will fit better together by creating a depression or a bowl nerves and bloods may travel through and around a bone through literal holes in the bones and those are and yeah those are some main reasons why you would have depressions are opening so go ahead and take a look at this list as well remember that we have I think this is a pretty good picture to see this particular aspect we're gonna be looking at the microscopic look of compactable and so in this picture we have both spongy bone and compact bone remember that both will be present in all bones now the compact bone is going to have these structures that are called osteons and I like this picture because it actually shows them in in relief in here that shows them how they actually look inside of the bone itself which is pretty cool this is what it actually looks like if you were to pull one of those osteons out of the bone you'd actually see those layers that surround the central canal this is a nice picture of them all stacked together and one that is pulled out so you get kind of get the idea here and osteon is the structural unit of compact bone specifically there's a series of lamellae that wrap around each other each of these are made of collagen fibers and they're made of alternating directionality of collagen fibers so not only is it strong cuz it's mostly made of collagen but the lamellae themselves are alternating directions so that it really resists twisting force it's very very hard to break a bone it is possible but it's very difficult to do because they are incredibly strong and because of the directionality of those lamellae in this picture of course is quite obvious to see the haversian central ascent hurt a version canal or the central canal here you can see the blood vessels and nerves making their way through there and again this is a pretty good picture that shows again an osteon here pulled out the haversian Center or the sorry the perversion canal hole or the central canal in the center and close up you can see the nerve vein and artery very vascular tissue here you can see that every single one of those haversian canals has a blood that has blood vessels and nerves so very vascular you'll see those canaliculi here this is probably best picture that's showing the canaliculi you'll see osteocytes sitting inside of the lacunae those tiny lakes in there and you'll see in this sketch you'll actually be able to see the little living cells inside of there and you'll be able to see the way that they send out their tendrils into the surrounding matrix through the canaliculi the tiny canals so the canaliculi will connect little Kuni eventually through a series of canaliculi to the haversian canal in the center and again this is showing those osteocytes like in in isolated too without the bone material you can see how they stick out their little arms through the canaliculi the last structure we want to take a look at are the perforating or Volkman z' canals the fact is is that it's not shown in this picture you have to get blood vessels and nerves into the tissue in the first place so here we're showing that the the blood vessels and the nerves come from the periosteum on the very outside of there but you know they have to continue on in a horizontal manner so there are canals in here called perforating canals that run horizontal to the length of the haversian canals or the central canal so here's a central canal and here's a perforating canal that helps to connect all these structures with each other