excuse me what a way to start huh anyway this is Professor long doing my anatomy and physiology lectures or my students at Del Mar College anyone else watching these videos might glean some useful information nonetheless this is muscle lecture 2 the second in the series we're gonna do the microscopic anatomy of muscle tissue the histology of the muscle so we can understand how muscles contract in the next lecture I did have some comments that I want that people wanted to see a little bit more of me and not just see my hands or my belly sticking off from the side so I reposition the camera if I don't like it I'm gonna go back to showing just a marker board hopefully you can read and see anyway so if you follow along in the note set this is on the bottom of page 52 it's asking you to draw this out you might need some more room so nonetheless when we look at a muscle let's say we took the biceps muscle out of your arm and we cut it open what we would see is that there's an outer connective tissue covering that surrounds the muscle and the muscle itself is a bundle of smaller units so when I look at a skeletal muscle the outer connective tissue covering is a structure called the EPI my seemeth epi means uppermost or outermost the mic comes from muscle the ems membrane so really it's just a big membrane of connective tissue primarily and inside of the muscle if I look inside of it there's some smaller structures that are bundled up and they look like long tubular structures as well so I'm actually I might change that color a little bit I don't know that orange shows up very well but nonetheless if I hold one of these structures out like this each one of these I'm going to put a little letter F on them there's a structure called a fascicle so a muscle is a bundle of fascicles and a fascicle has an outer connective tissue covering and this connective tissue covering this called the peri my seal for perimeter so the perimysium is made out of the exact same tissue as the epimysium they're the same stuff but one is wrapped around a smaller structure called a fascicle and if I take several fascicles just like me taking several of these markers if I were to wrap something around them then I would have a muscle the outer covering would be the epimysium the plastic of the marker would be the perimysium and each marker would be a fascicle i'd have a bundle of those now when we look at a fascicle fascicle is a bundle of smaller structures so when I look inside the fascicle I'm gonna see these smaller units inside of it now if I pulled one of these out and make it a little bit bigger than the others just so we can see it this structure is called a Myo fiber which is a muscle cell or a muscle fiber it goes by three names muscle cell muscle fiber myofiber you know most cells if we were to magnify them like we did in lab and look at them most cells would be about the size of my thumbnail when magnified you know 400 times or so well muscle fibers are long narrow cells so originally they thought they were fibrous like the fibers of a rope later on I think someone figured out histologically that they were actual cells with mini nuclei and a lot of the organelles so the word muscle fiber morphed into muscle cell they're the same thing now just like any cell and as a cell membrane but because the properties of muscle cells muscles fall into a category of cells called excitable cells the cell membrane of excitable cells is very similar to other cells it's a lipid bilayer with proteins and carbohydrates and cholesterol and other things associated with it but it's audible cells have a lot of what we call gated channels little integral membrane proteins that act as like tunnels that things can flow through and some of them are gated in that they can open and close and allow things to flow through or not so excitable cells have a lot of these gated channels and because the cell membrane of a muscle cell is a little bit unique compared to other cells the cell membrane of the muscle cell is called the sarcolemma now outside of each muscle cell there's another connective tissue covering that surrounds the muscle cell made out of the same stuff as the EPI and perimysium and so if I were to draw this around this there's a lot of different connective tissue fibers a lot of collagen fibers and other things going in all these different directions and each individual muscle cell is individually wrapped so now imagine if this marker were a muscle cell and the marker itself has a connective tissue covering or actually has a sarcolemma the cell membrane if I can wrap this with a piece of paper then that would be the connective tissue covering surrounding each individual cell that connective tissue covering of each individual cell is called the endo my scene so we actually have three layers of the connective tissue covering epi carry and endomysium all made are the exact same stuff if I take the perimysium let's write an epi my sim and wrap it around a bunch of smaller structures called fascicles I get a muscle so a muscle is a bundle of fascicles the fascicle is a bundle of muscle cells or myofibers or Myo Myo fiber muscle cell or muscle fiber and the connective tissue covering surrounding the fascicles perimysium each individual muscle cell has its own cell membrane called the sarcolemma and outside the cell membrane as a sleeve that sort of surrounds it are individually wraps it called the endomysium turns out the endomysium has two major functions that we're going to discuss number one it individually isolates or electrically insulates each scale Atoll muscle cell from each other so if a bunch of people were touching skin-to-skin and several of us were we're touching each other imagine if I took a hundred people in bathing suits you know speedos and bikinis and we were all standing crammed into oh say a phone booth or some small space if one person licks their fingers sticks them in a socket please don't do that it will kill you but if someone got shocked someone got tased then everybody would feel that voltage it would shock one person and then pass through contact to the next to the next to the next if everybody put a giant rubber suit on and then we crammed you all together and I could tase one person that person would can their muscles would contract and the people around them might feel them contracting but they wouldn't feel the voltage and their muscles would not contract because we are insulated by that rubber suit that's kind of what the endomysium does connective tissue does not conduct electricity very well so if I were to go and shock this muscle cell and cause it to contract the other muscle cells surrounding it would feel the contraction but they wouldn't feel the voltage they wouldn't contract by themselves the second major function is this endomysium from each muscle cell as they come down towards the end of the muscle because each muscle cell runs the entire length of the fascicle they are somewhat tied together at the end it would almost be like me taking you know several ponytails if I still had long hair like I used to and braided ponytails and then I braided the ponytails together each individual muscle cell is braided sort of together at the end of the fascicle with each other so that they're all pulling on the same piece of connective tissue at the end and that connective tissue since it's the same as the Paramecium is all woven together and all of the fascicles are somewhat woven together into the perio epimysium sorry and at the end of the muscle all those connective tissue coverings that fan out through here form a tendon essentially what happens then is when a skeletal muscle cell contracts and pulls on its endomysium its pulling on the end of the fascicle and its pulling on the tendon at the end of the muscle later on we're gonna see how that allows us to increase tension in a muscle there'll be several ways that we can do that two ways that we can increase tension in a muscle and one of them is going to be to increase the number of muscle cells pulling on the tendon as a little side drawing over here let me show you if I were trying to pull a car let's say a car is stuck somewhere I could have a person pulling on a rope if I had another person with another rope and I rated those ropes together then each one of them can provide 50% of the force on this piece right here which would then be applying pressure to the car if one person pulls I only get 50% of the force if the second person pulls I can get 100% of the force and of course the more people I have the less force each one could generate overall and the more control I would have over the muscle that's exactly what's happening here each muscle cell is like a little person pulling on its own individual endomysium but then they're all woven together into a parry and a epimysium that forms the tendon connected to the bone I hope that makes sense to you anyway so now we understand somewhat some of this structure now what I'm going to do is I'm going to race a lot of the information and I'm going to show you a little bit more detail and actually what I'm going to do is I'm going to stop this video in a few minutes I may not get to finish everything and I may have to make it third video as I've stated before managing the size of the files becomes issue but if I look inside a muscle cell so now I have my muscle my fascicle and my individual muscle cell with that circle limb okay inside the muscle cell there are smaller subunits that happen to be called myofibrils so the muscles above them fascicles a fascicle is a bundle of muscle cells and each muscle cell is a bundle of smaller units all these long tubular structures that are made almost entirely on a protein called a mile fire drill now one of the things that I know about the myofibrils is that they don't have any kind of connective tissue covering or anything wrapped around them it really looks like a long tube essentially though a myofibril is a bundle of smaller structures and there's these little tiny proteins if I look on the end of a myofibril let me draw this on the little bit bitter there's a bunch of little proteins in here that are like little stick like proteins running the length of the smile fiber oh they'll be interrupted by these little lines are these other plates of proteins but these repeating units are gonna last the entire length of each one of these myofibrils there's a second protein mixed in here I'm going to try to color code it like our textbook does so I'm going to try to use purple and pink or purple and red but these proteins are sort of interspersed with each other this way so if I look on the end of the myofibril and I didn't draw this anatomically correct the way that it's uniquely arranged but nonetheless what I see is I'll see these little red proteins and then these purple proteins and then the red ones and the purple ones and they're gonna repeat throughout the length of a myofibril I'm gonna draw one more of these I'm gonna take this myofibril out and I'm gonna run it all the way through here as if it was running through the muscle cell so essentially I'm gonna have these little red stick like proteins and they're really not even solid it's not a solid circle I can have a protein here a protein here protein here one here and some more over here okay they usually actually organize themselves in groups of six in a very unique arrangement and then they kind of end and then there will be another grouping of them like this that are connected by a series of other proteins and then some will stick off this way and we have these repeating units maybe this is the end of our myofibril I didn't draw exactly everything perfectly and matched up but you'll get the idea there's another plate like protein that really kind of runs around here and it's a bunch of proteins that are interconnected and sticking off of this plate there's this other purple looking protein in reality they're not pink and purple but these are the colors we assigned to them everywhere that I see one of these lines would be one of these solid 3d plates and these would be in the middle here and there would be three of them surrounding every one of these other red proteins will get into that structure in a loop okay you can see these repeating subunits the structure from here to here to here and they would continue to repeat all down the length of each individual myofibril the proteins that make up the myofibrils the two proteins found in here are called actin or the thin filament and your book will use the term milo filament and filament interchangeably myofilaments from the word muscle mile and the purple one is referred to as the thick filament and it's primarily made up of a protein called myosin so we have two myofilaments or two filaments that make up myofibrils there are other proteins involved act and then tighten and connected I mean tighten and connected and some others but we're going to focus on these for the time being so one myofibril this long tubular arrangement of these two proteins or myofilaments called actin and myosin or the thin and thick filament now technically the thin filament is made up primarily of actin but I will use the terms interchangeably and the thick filament is made up primarily of myosin but I'll use the terms interchangeably as these proteins are arranged in a certain pattern and that pattern repeats down every myofibril what we're going to see is that these two proteins are going to slide together in a moment we're going to look at the structure of actin and myosin from a microscopic or molecular level I should say and we're going to learn that the myosin filaments are going to reach out and grab on to an actin filament and pull it and what they'll do is they'll pull towards this solid line in the middle it's called an EM line for middle and these little zigzag shaped lines are going to be called Z lines so we're going to draw the structure out in the next video and what's going to happen is when the myosin filaments grab the actin filaments and pull and we'll pull the Z lines closer together shortening one of these subunits called a sarcomere if I shorten this one this much which would pull this one over and shorten it which would pull this one over and shorten it the entire myofibril shortens when these proteins slide across each other it's what we call the sliding filament theory in muscle contraction and as each myofibril contracts the muscle cell contracts and pulls on its endomysium which pulls on the perimysium at the end of the fascicles which pulls on the tendon at the end of the Epis in of the entire muscle so it's really these protein interactions the sliding filament theory where these two myofilaments slide across each other causing the muscle to contract we're going to look at the molecular structure of these proteins in the next video it'll be muscle video in three so I hope you learned something here hope that this was helpful and you understand somewhat of the anatomy or structure of a skeletal muscle and every one of the skeletal muscles that we've been learning in lab flexor carpi radialis flexor carpi ulnaris brachialis spiceps brachii brachialis triceps brachii brachial radialis all of these muscles rectus femoris they all have this structure this is the structure of skeletal muscle all right all right I hope you have as much fun as I did another video coming soon