hey everybody Bob long your anatomy and physiology professor del Mar College for those of you that are enrolled in my class this is for part 1 a.m. P this is muscle lecture number 3 the third in a series of lectures again I'm trying to keep the muscle lectures or all of my lectures to about 10 to 15 minutes as much as possible under 20 minutes simply because of the difficulty of managing files and uploading stuff and also for you to be able to keep up with the worksheets that I've printed on my canvas page or in the note set so anyway as we discussed last time we went over the structure of muscle from the muscle to the fascicles to the muscle cells actually I didn't draw this quite correctly but if this were a fascicle this would be a muscle cell this would be a myofibril so anyway what we're going to start looking at is the structure of the myofibrils and the myofilaments actin and myosin as we discussed them in the last video so what I'm going to do is I'm going to cut out a section essentially this section right here of this myofibril I'm essentially going to cut out a structure called a sarcomere and we're going to draw it out and learn it together if you're trying to follow along in your notes then the structure of the sarcomere is gonna be on the bottom of page 53 and there are some definitions at the top of the page that you should fill in if you have your notes set all right so look if I were to take this structure the easiest way to do this is over near the edge of your page wherever you're drawing draw zigzag shaped line like this that essentially has four points we're going to have some little red lines coming off in this direction which would be these little proteins over here and then I'm gonna have some red lines coming off and I'm gonna go over a specific distance I'm gonna make all of these lines the exact same distance in between each one of those I'm gonna color code this so it matches our textbook but overlapping just a little bit not all the way over I'm gonna draw four lines that run a long ways across the board here now on the other end overlapping the same amount or roughly the same amount I'm gonna draw formal red lines like this and then I'm going to connect them like so and then sticking off here would be these proteins on the other side now running right down the middle there's going to be a thick band like this okay I'm gonna fill this in now what we are seeing is sort of a flat structure two dimensionally but in three dimensions this would actually go around sort of an arene like this and go on the other side so that we're looking at a sort of a rounded tubular structure of protein this structure these zigzags shaped lines get a specific name so each one of those zigzag shaped lines is referred to as a z line so at either end I have a Z line and the area that covers from Z line to Z line all the way across is known as a sarcomere Soaker sarcomeres are repeating subunits there's a sarcomere here and here and they would go all the way down the length of these myofibrils they would continue to the other end as well and every myofibril it's very unique and a highly ordered arrangement of these proteins now the little red lines represent the protein called the thin filament and sometimes I use the term actin interchangeably in us 100% accurate but this is our actin filament or in filament and the little purple lines are going to resent represent the protein myosin or the myosin filament or thick filament and the line right down the middle of the sarcomere is called the N line this is going to get a little bit messy but you got to learn to practice and draw this out so that you can understand cuz it will help us understand how muscles contract when we get to the next lecture now a sarcomere extends from z line to z line and then we'd have another sarcomere from z line busy line and so on within the sarcomere there are sub regions one of the areas of the sarcomere and i'm going to try to use some different colors here that is comprised of the area that has only actin filaments and quite honestly if i were to look at it it would go up here from here to here on either side of the Z line including the actin on either end this area of a sarcomere and has actin only as no doesn't I bend and if that's an i bend in this area over here that has actin only this is an I Bend if you're trying to define this a sarcomere goes from Zeeland the Z line a Z line is sort of a 3-dimensional plate of proteins to which the actin filaments or din filaments are anchored so these are attached here imagine if I could cut this and turn it sideways I would have a big dream of protein like this and I would have these little sticks sticking off in two directions sort of three dimensionally so this is a solid plate almost as if I stuck a bunch of Spears in the wall and they were sticking out at you the wall would be the Z line the Spears would be the actin filaments the same thing happens here at the end line the in line is a solid plate of protein to which myosin filaments are attached and the area in the middle of the two eye bands that goes from the end of the myosin filaments to the end of the myosin filaments all of this area right here is referred to as an a band now the terms I and a come from you know back in the I believe the 20s and so 20s or 30s scientists figured out how to make a bunch of light waves travel in the same direction instead of spreading out and when light was traveling in all the same direction they called it isotropic when they shine isotropic light on different things sometimes they see things that you can't see with what we called a light or regular light light that's being scattered in a number of directions well they started looking at everything they could under the Sun with isotropic light and seeing what happens when they were studying skeletal muscle tissue and shined isotropic light across it what they realized is that on the wall they would see a light band where the isotropic light was blowing right through and showed a light spot and then the thick filaments that light would hit it and scatter and it would create a shadow so they call that an isotropic light and then they had another band of isotropic light and when you look at skeletal muscle under a microscope as some of y'all probably done by now you notice the dark bands and the light man and a dark band and a light band in a dark band the dark bands are the a bands the light bands are the eye bands and it's because these thick filaments scattering light creating the shadow and the light blowing right through where the thin filaments are anyway that's where the names came from so one sarcomeres divided into three bands eye band a band event each a band is divided into smaller regions and we refer to these as zones so now this picture has gotten a little bit messy and I really don't want to erase anything I'm gonna have to so I'm gonna erase this up here but I think you see the idea of how it all fits together so when I erase all of this up here within my sarcomere if I look at my sarcomere and I'm gonna rewrite some of this sorry this isn't working out exactly as I had hoped but that's okay we're gonna make it work so when I look within my sarcomere here there are different areas of the sarcomere and again the sarcomere goes from zi to Z line over here this area of the sarcomere that has both actin and myosin overlapping on both sides here like look in this region I see actin and myosin in the eye band I only see act in this area I see actin in my overlapping some Pulu asterisk here and that stands for an area called the zone of overlap of zone of overlap has actin and myosin overlapping each other which creates this final area in between the two zones of overlap where I see myosin only and of course the M line in this area that goes from this zone of overlap to this zone of overlap the area in between I'm gonna put a blue asterisk there that is called the H zone or some books call it the H band so I learned it's sort of this way a sarcomere has three zones I'm sorry three bands I band a band I bend the a band is divided into three zones zone of overlap H zone and a zone of overlap the I band within a sarcomere is the area or the region within a sarcomere where we see only the actin filaments so the Z line is where the actin filaments are incurred the area of a sarcomere that we call the H zone is the area where I see only the myosin filaments and no actin and it also includes the M line in the middle the zones of overlap or that region the sarcomere that contain actin and myosin overlapping and then if I put the zones of overlap plus the age zone together I get the a bed so you can write out the definitions of these things this way I'm going to try to follow the order that's in my notes it so a sarcomere is a region that extends from one z line to the next and it is the contractile or functional unit of the muscle the Z line is a 3-dimensional plate of proteins to which the actin filaments or thin filaments are anchored the M line is a 3-dimensional plate of protein to which the myosin thick filaments are a current the Iban is the region of the sarcomere that contains only actin filaments the a band can of zone of overlap plus an H zone plus a zone of overlap the H zone has myosin only the zone of overlap has actin and myosin filaments overlapping each other those are sort of the verbal definitions or descriptions of a sarcomere now in a sliding filament theory which I mentioned in the last video what's going to happen is in a minute we're going to do another video where we look at the actual molecular structure of actin and myosin and what we're going to see is that the myosin filaments have these little tiny heads and the little heads of the myosin filaments will stick out like this and they're stacked almost like little golf clubs because there's so many of them laying over each other it makes it very thick and they'll stick off in a number of directions and all these little myosin molecules are stacked like this and given the opportunity when we understand the three-dimensional structure these little myosin heads can extend up and grab on or bind to and attach to the actin filaments and when they do this in both directions they will literally grab on to the actin filaments like my arms grabbing a rope and pull and when this happens on both sides and some of them are attached while others are still reaching up when they grab and pull they'll pull the two z lines towards the M line causing a sarcomere to contract and if you go back to the last video I look at the length of a myofibril if each sarcomere contracts just a little it will pull the ends of the myofibrils towards each other shortening them since the myofibrils are attached to the ends of the inside of the muscle cell it will contract the muscle cell since the muscle cells endomysium attached to the end of the fascicle and tied into the the Perry and epimysium of the muscle when the sarcomeres contract and the filaments slide past each other like this then the myofibril contracts the muscle cell contracts the fascicle contracts and the overall muscle contracts so muscle contraction really begins with the interaction of these small proteins the myosin or the tendon thick filament so now that we know the structure of a sarcomere we'll talk about the molecular structure of actin and myosin in the next video and then we'll talk about how do muscles actually contract it's a series of steps and then finally we'll talk about muscle performance and you'll take quizzes after each one of these those of you that are in my class the rest of you I hope that you glean some information from this and it was helpful so I hope you have as much fun as I did hope you learned something thanks