our engineers so in this video we're going to continue on with what we finished up with so if you guys remember we talked in the recent video in part one which if you guys haven't seen that you guys got to go and watch that first ok then we're going to go over in this next video we're going to talk a little bit more about the myofibril so in the recent video we took a skeletal muscle right we took that belly we've made a transverse cut we look at that transverse cut and we saw the connective tissue coverings that are surrounding each layer right so for example the muscle belly is covered by a connective tissue called the epimysium then inside of that muscle belly we have these things called fascicles and fascicles are just bundles of muscle fibers and then each one of these are a fascicle all right and then around them around that fascicle you have a nice connective tissue covering which we showed right here that was called the perimysium then in this fascicle there's individual muscle fibers what we did is we pull one of those muscle fibers out which again you can call muscle fiber a muscle cell there's a connective tissue covering that muscle fiber which is called the endomysium which is an areola connective tissue and then we said that you have a lot of dis filamentous filamentous endoplasmic reticulum structure which we call the sarcoplasmic reticulum it's a nice calcium storage Factory we said that striated which means it's striped and that's do this actual connection of thin and thick filaments that we'll talk about which is going to be making up the basic functional unit called the sarcomere and then we said it's multinucleated and we said that the muscle fibers are cylindrical and we said each muscle fiber is surrounded by a plasma membrane which we call the sarcolemma ok then we took and there's thousands hundreds upon thousands of these myofibrils which are just many many different connections of fixed elements and thin filaments and accessory proteins that we'll talk about and that is our myofibrils and what we did is we zoomed in on a portion of a myofibril and now we're going to talk about that all right so first thing that we're going to do is I'm going to lay out some different zones and regions and stuff like that because that's going to help us to continue to keep narrowing down protein after protein because literally that's all this whole basic myofibrils composed up as proteins so let's do that first so the first thing I'm going to do is if you see this pink just exact protein going all the way up this protein is actually going to be called the Z disk okay that's the Z disk and we'll talk about what protein it's made up in just a second on this one over here this is another zigzagged protein and we're going to call this one a z disk from z-disk to z disk is your functional unit of the muscle fiber right and the Z is to Z disk this is called the sarcomere from this Z disk point here so let's say I go from this point here from that z-disk all the way over here - that's Z disk this whole length is consisting of the structural and functional unit of this myofibril and that is called the sarcomere okay that is our sarcomere and the sarcomere is again the distance from Zedek to z disk now in that circle mirror there's a couple other structures that I need to talk about in this we have this thick thick filament this red thick filament this big rectangular box that big rectangular box there is called the thick filament and gets called the thick filament so again what is this red box right here that right there is specifically called the thick filaments all right now the thick filament if you look here's this whole thick filament right here this thick filament on this end you see these blue these nice little baby blue proteins right here they're linking this thick filament to this z disc and the same way these proteins are linking this thick filament to that V disc the same situation is happening over here look at the end of this thick filament you have these nice clearly like blue proteins linking the thick filament to the Z disc as well as this protein is moving through the thick filament and linking it to these green proteins running right down the middle of the sarcomere alright these blue proteins right here are called chitin alright chitin so this protein right here is specifically called chitin all right it's called chitin so these blue proteins right here called Titan and they're very special we'll talk about why they're special in just a second okay but again remember the Titans are anchoring the sixth element to the Z disk also they're connecting to these proteins that are running right down the middle part of the sarcomere what do these proteins here call well first off before we name these proteins what is this whole line here call this line right here is specifically referred to as the M line so these proteins here all the way up makes the M line alright so there's a bunch of a bunch of different proteins and as you look at one watch the M line as it goes up M line goes up goes up goes up and it connects to what is this protein Titan okay so if you look the M line which is running right up the middle of the actual sarcomere which is consisting of two main proteins we'll talk about a second is linking the actual Titan also to it so if you look this is connecting to the Titan what's the titan connecting it's connecting the stick filament to the actual z disk so Titan is helping to stabilize the thick filament and it can do that by not only anchoring it to the Z this but also anchoring it to these accessory protein structure called the M line whatever proteins is the M line made up of the main one that's made up of is called my Oh Mason my Oh Mason so my own Eason is one of the main proteins that is a part of the end line there's also C proteins there's another really important protein which is called creatine kinase but it's more of a functional protein rather than a structural protein but they are scattered along the m1 so these are three really really important proteins that are making up the M line and one of the proteins is called my Oh Mason the second one is called C proteins and the other one is called creatine kinase but again increasing kinase I'll star this one and the reason why is because it's more of a functional enzyme we'll talk about that when we talk about the metabolic actions of muscle fibers okay now again what's the function of the M line the M line is responsible for connecting these are accessory proteins it's connecting the Titan and the Titan is connecting the stick filament to the z-disks so it's acting as accessory proteins that can help to stabilize the thick filament that's their function Titan what do we say was the function of Titan it's actually stabilizing the thick filament by anchoring the sixth element to the z disc and it's also connecting with these accessory proteins of the M line all right sweet now here's the next thing from the end of this thick filament to the end of this thick filament we call this AB and it appears like a like a nice dark band when you look at it there so let's what is this band distance right here let's say I come from this point about right down here so I'm going to go from about right here all the way to about over here this whole distance right here is consisting of what's called the a band okay and the a band stands for an isotropic and isotropic hair I'll write that for you for those of you who want to know it and all it means is just a darker it's means that's a dark band okay so an isotropic just means it's a dark band so the a band is the entire length of the thick filament okay now from this thick filament end to this thick filament end over here I'm going to come down here I'm going to go from this point here to about approximately this point right here so now I'm going to come down from this point to this point so I'm going to continue off of this point I'm going to come to about right here approximately let's make this one blue we'll go to about right here it's not perfect but it's approximate this is called D I band okay this is called the I band and the I band specifically stands for it stands for isotropic okay so it stands for isotropic which just means it's a lighter color okay so it's same thing over here we follow it over here coming down from this point here approximately to about this point right here approximately this point right here is called the I band and again I stands for isotropic if you want to know that I'll write that down there for you it stands for isotropic and that just means again that it's a lighter color okay so I'll write isotropic over here for you guys too so so far what do we know we know we have a sarcomere which is from z-disk to z disk we know that we have an M line which is a protein running right down the middle of the sarcomere which is consisting on miami's and c proteins increasing kinase we also know that you have this stick filament and from one end of the thick filament to the other end of the sixth element is an a band standing for an isotropic which just means that it's a dark band on this end of this thick filament to the end of this thick filament on another sarcomere so for example this is a sarcomere here right we'll call this sarcomere one on sarcomere two over here could be sarcomere one so on sarcomere one from this end of this thick filament on sarcomere two to the actual end of this thick filament on sarcomere one that distance right there is the eye bent and the eye band stands for isotropic which means it's a lighter color okay now if you look here we have a whole bunch of proteins coming off of this bad boy right here this big big protein structure right here we're going to call this whole thing to thin filament okay so we're going to call this whole component here this whole all this blue the orange the green the black this is all the thin filament all right now the thin filament is directly connected to the Z disk through this black protein that's running right down the actual middle of its building the foundation for it that black protein that's running right down the middle of this is called nebula so again you can see right here so this is a thin filament this is a piece of a thin filament that's a thin filament and this is a thin filament and again connecting this thin filament to the Z disk is this black protein right again what is that black protein they're called this black protein is specifically called nebula okay nebula is a protein that's anchoring this whole thin filament structure to the z disk all right now you see these blue proteins right here that's making like a nice little supra molecular helix that's called actin but here's the thing with actin there's two types of actin mainly so we're going to talk about so let's say I take one of those individual structures they're just one individual circle that one individual circle that kind of like kidney bean-shaped if you actually look at it in a normal way it's actually called g actin so a monomer of actin is called g act let me write that down this is a monomer but then let's say i polymerize this bad-boy and when undergoes this polymerization let's say i take a whole bunch of these badboys a whole bunch of these g actin molecules and connect them together if I start doing this now now this is called F actin okay so now this is called F acting now what happens is when I take this G actin and I make this new actin called it's called the filament asia's acting or I just like to call it the filamentous actin and then G stands for globular actin so when I go from globular actin to filament it actin it's just because I'm polymerizing these guys so this is a polymerization reaction now all that happens is to just be simple let's say this is a monomer of F actin and I take another monomer of F actin and I take and make a helix like structure and that's what you see here for this Acton okay so when you look at this act in here it's looking like a supramolecular helix which is consisting of multiple actin molecules okay so this blue structure right there is specifically called actin all right so that's our actin molecule all right so we got actin here and again nebula is this black protein anchoring this thin filament to the z disk actin is this whole little super molecular helix consisting of again G actin being polymerized into F actin in a multiple f-actin is linking together to make this super molecular helix then you see it's orange protein right there this orange protein is like a wire so here I want you guys to imagine something for just a second let's say here in each one of these s Acton's I have a little hole a little hole and that hole is where this protein called myosin binds well there's that orange protein and what that orange protein does is it actually wraps around these holes and blocks the myosin head from being able to bind so what this protein is doing is coming and surrounding and blocking these little these holes what are those holes hold these holes are called the active sites so what this broke like protein is doing is it's coiling around this actin and blocking the active sites in a resting position so whenever the muscles are resting this protein is rope like protein is blocking the active sites what is that rope like orange protein call it is called Tropo myosin so look at this orange protein here this is called Tropo myosin okay so tropomyosin and again what is the function of tropomyosin tropomyosin normally when the muscle is at rest is blocking the active sites on actin preventing this myosin head that we'll talk about in a second from actually binding okay so if we have this triple myosin again what is it doing just one more time it's acting like this little this red ro protein right and again this is actin these little holes are the active sites that's where the myosin it that we'll talk about in a second binds to cause contraction when our muscles are arrest this cord like protein called tropomyosin is blocking the active sites preventing the myosin from being able to bind on we'll talk about what allows for them to move and open up those active sites for the actual myosin heads to plug in in the neuromuscular Junction video ok that's our tropomyosin which is a part of the actual thin filament now if you look here we have this little green protein let me expand a little bit on this green protein for a second ok let's say here I have this green protein and one there's three different sites on this green protein one of the sites is binding to this blue protein that we called actin the other site is binding to the orange protein that we called tropomyosin so if one over here is binding to again what would this one be binding to it could be binding to actin or the other one could be binding to troppo myosin and then this part here is specifically binding to calcium okay so this has three different sites in other words we're going to call this whole molecule this whole green protein molecule we're going to call it troponin okay this is called troponin this whole big molecule up here is called troponin but now we got to be a little bit more specific the site on troponin where calcium is buying is called troponin see that's easy because there's calcium and calcium starts would have C so this point here is called troponin C but I'm going to put just T and C okay so that site right there where the actual calcium is binding is called troponin C this point right here where the actual troponin is binding to the tropomyosin is called tropa troponin T and that's simple because tropomyosin starts with a T so this site right here is called troponin tea now here's where you guys be like oh yeah this one wants me troponin a that's wrong all right it spun troponin a it's actually called troponin I and the reason why it's troponin I is because I stands for inhibitory okay and we'll talk about that more neuromuscular junctions once you guys get the structure down first cuz if we get the structure down down pat we're really going to understand the function okay so again this whole green protein molecule is called troponin but there's three different sites on this troponin one that binds to the tropomyosin is called troponin t the part that - ed the calcium is called troponin C and the part that's binding to actin is called troponin I okay and these are good markers for certain types of heart to heart damage right so if someone is having a heart attack some of these actual proteins might leak into the actual blood stream and could be an indicator for a myocardial infarction which is a heart attack right specifically in cardiac muscle we're talking more about skeletal muscle okay so that covers that part so again what is this green protein here called that is called troponin all right so we've pretty much covered the thin filament let's review the thin filament one more time black protein is nebula this blue protein is actin the orange protein is tropomyosin and the green protein is troponin okay we covered the sixth filament a little bit but now we have to go into a little bit more detail in the Styx element this thick filament is having coming off of it this little like tail so you see a little too like tail right here it looks like it's coiling this because it is there's two protein chains so this is actually going to have this little protein change this little alpha helix like structure so there's like a little alpha helix here okay and what happens is this is the tail part of myosin so this whole protein here is called myosin so again what does this protein here called guys this whole protein right here is called myosin now myosin is made up of three parts this part right here is called the tail now guys called the tail this mid part here is called the neck and there's top part here it looks like a double like head like for example if I were to kind of show it like this let's add here here's that part the tail here's the neck and there's two heads okay so again this part here is the tail this part here is the neck and this part here is the head why is that important the head is what binds into these actin active sites so you see these little holes right here in the actin that's what the head binds into and allows for this moving or sliding of these myofilaments again all these Maya filaments are just all these protein structures okay that's that's the function of the head another function of the head is that it has an enzyme component on it and we'll talk about that more but it's called a myosin ATPase in other words it can cut ATP and break it into ADP and an inorganic phosphate so it has what's called ATPase activity it can cleave ATP into ADP and inorganic phosphate which is also important for the sliding of the monofilament the neck region is important and the reason why the neck region is important is that there's what's called light chains so let's say here I have a blue chain here we call that a light chain and there's another one you have unless you have another chain over here binding to the other side for a second these light chains are really really important because these light chains not only do they support the actual head and the neck region of this myosin but they also can undergo regulation so for example one phosphate ions bind onto these light chains for example their myosin light-chain kinase is that can also control the activity of this myosin molecule so again myosin if the assisting of a tail which is looking like an alpha helix has a neck which consists of light chains on if you really want to know the light chains you have what's called regulatory light chain okay that's one of the actual light chains let's just say that's the green one the other one is going to be the essential light chain okay so the regulatory light chain is what can undergo phosphorylation and help to change the activity of the myosin the essential light chain is more structurally stabilizing the myosin head and the myosin neck okay so we got the myosin now okay so in short here what do we have so far what have we been able to cover we have the Z disk I didn't tell you what the protein is making up the Z disk there's many proteins but the main one that's making up to Z disk the main protein is called alpha actinin do not get that confused with actin so the main protein of the z disk is the alpha actinin that is the main protein of the z disk alright so now let's do a quick review of this real quick all right this whole whole big myofibril structure so one more time we have the a band which stands for I and isotropic what is an isotropic mean it means that it's darker what is it primarily consisting of just thick filament all right so it's going from this end to that sixth element to this end abetik filament on the same sarcomere what determines the sarcomere it's from z disc 2 z disc that is our sarcomere ok Ibans stands for isotropic which means it's lighter colored what is that consistent of if we come up here it's going from the end of this stick filament on this sarcomere to the end of this thick filament on another sarcomere adjacent to it that is the actual Iban and it's primarily consisting of what if you think about if it's only taking this distance it's only consisting of like the z disk it's only really consisting of this thin filament proteins right that's all it's really consisting of so really if you think about it the Iban is really only consisting of the thin filaments and it's also consisting of like a Titan and a little bit of a z-disk structure right then we have the M line and the M line is these actual made up of Miamian proteins and C proteins and creatine kinase enzymes that are running all the way up through the middle of the sarcomere okay and again what are they doing they're linking to this Titan structure what is Titan doing Titan is anchoring the thick filament to the z disk on top of that Titan is also connecting to this M line proteins this stabilize the structure of the thick filament okay oh we got another one that we have to cover the distance I'm going to get rid of this part here the distance from this thin filament to this thin filament over here what is this right here called so the distance between this thin filament and this thin filming on the same sarcomere is called the H zone this is the ages ohm okay so again one more time age zone is the distance from this thin filament to this thin filament on the same sarcomere okay all right so we got that then what else do we say we have the thin filament what are the main proteins of the thin filament the blue protein is called actin okay and what do we say about actin actin is originally in monomeric form called g actin which stands for globular actin when you polymerize a bunch of those g Acton's you get F actin which just stands for filament it actin right this filament Acton can actually have an under can act as a monomer bind with another monomer and form the Supra molecular helix and this reaction occurs by polymerization the other protein was this orange protein which is called the tropomyosin tropomyosin is responsible for covering the active sites of the actin during rest so that the myosin head can't go in there and bind in but whenever we have a situation what is that other protein that we talked about we talked about troponin troponin has three different sites that you can bind to one is when it's binding to triple myosin the other site is when it actually combine to calcium and the other one can bind to actin if it's binding to calcium which is called the troponin C site if it's binding to troponin it's the troponin T site if it's binding to actin is called the troponin I site a real quick pre alluding to a we'll talk about an excitation contraction coupling is when calcium binds them to the troponin right it changes the shape of the troponin T component and when it changes the shape of the troponin T component it pulls on the tropomyosin and when it pulls on the tropomyosin it opens up those actives for the myosin head to plug in okay and then cause the the movement of the myofilaments then we say that this black protein that's running from the z disk all the way to the end all the way the length of this thin filament is called nebula and it's acting as a supportive structural protein then we said that this thick filament is having a protein coming off of it called myosin and again myosin has a tail region it has a neck region and it has the head region head is responsible for binding it to the active sites of the actin and moving the Maya filaments it also has an ATPase component that it can cleave ATP into ADP and inorganic phosphate and the neck can have proteins bind on to it that around this which are called light chains and there's two different types of light chains regulatory light chain which can bind the phosphate and change the overall shape to play a role in contraction or essential light chain and that stabilizes the neck in the head all right and then again we said that we had the H zone which is the distance from this thin filament to this thin filament now I need to talk about one last filament which is so extremely important we need to talk about this one okay so let's say over here I have this actin I have another protein a very very important protein that connects the actin so here's this protein right here and what this protein does is it links the actin to the extracellular membrane so what is that let's say here we have the membrane of this muscle cell here's the membrane okay and you know the membrane is actually consisting of a phospholipid bilayer so let's say here is the actual muscle cell membrane there's so many different proteins that this dystrophin is linking to on this sarcolemma so what is this structure here called it's called the Sarco lemma okay there's so many different proteins I'm just going to draw a crude diagram right here and I just don't you guys to understand that there's a whole protein complex here and what's happening is dystrophin is linking the acting you see here is this blue protein called actin dystrophin is linking actin to the actual cell membrane through this whole protein complex and what happens is outside of our cell we have an extracellular matrix which consisting of a lot of different types of fibers what happens is these proteins can link to this extracellular matrix so now imagine what would happen because I hear this a lot you know tutoring is that people will constantly say all these proteins what do I really need to know for they're not even relevant they are and the reason why is look at this one protein this one little protein that we're talked about called dystrophin so again what does this protein here called this green protein it's called dystrophin and what dystrophin does is it links the actin to the sarcolemma through these actual protein complexes which link those proteins to the extracellular matrix if there is a situation in which there is a mutation in the dystrophin gene a mutation the dystrophin gene and they don't produce any dystrophin this can lead to what's called a muscular dystrophy so now we want to talk about it I just want to do a little pig bit on situations in which this dystrophin protein is actually they're not present or it's mutated because it's all clinically relevant because being a good you know either doctor or PA or nurse whatever you might be going into the medical field it's not just good enough to know the physiology it's good it's really important to know what happens if this protein breaks down or if this protein doesn't work that's where it's really clinically relevant so I'm going to come just provide a little tidbit in the situation in which this actual dystrophin protein isn't produced or it's mutated it falls under an umbrella of what's called muscular dystrophy right so there's there's many different types of muscular dystrophies we're going to talk about the two most common ones so out of the many types we're going to talk about Dushane really briefly and then we're going to talk about becker now out of these two keep it super simple muscular dystrophies is usually an x-linked it's an x-linked recessive disorder so it's usually an x-linked recessive disorder in other words it's more common in males so males are more likely to develop muscular dystrophy as compared to females and the reason why is males only have one X chromosome females have two X chromosomes so if they do what's called you know the inactivate ionization of the actual other Eckstrom of them that they have there's less likely of a chance that they'll develop this muscular dystrophy now Duchene muscular dystrophy is much much more severe okay in this situation the individuals who develop this type of muscular dystrophy is usually the development by the age of like five or six years old okay so usually these individuals develop by the age of like five or six years old now what is the difference then if really it's an x-linked recessive disorder and it's due to the dystrophin gene what's really the difference between Duchene and Becker well Becker is not as severe it's less severe it's still it's still bad it's still a terrible disease it's less severe but it takes a little bit longer for the actual onset of the disease to develop so usually this develops by the age of like ten by age of like ten and we give it a nice range to about twenty years old and here's the real big difference genetically I want to get into into the depths of genetics we'll talk about this more in detail in the path of his video but if you don't produce the dystrophin protein so just know dystrophin protein that's due Shane's okay so the lack of dystrophin so no dystrophin produced causes Deschenes muscular dystrophy okay so usually this is a result of what's called a nonsense mutation a nonsense mutation when you have a premature stop codon and the mRNA and the protein doesn't completely develop the second type is a frameshift mutation where there's like an insertion of an extra nucleotide or the deletion of a nucleotide and that can result in changing the reading frame and results of the the inadequate production of a functional protein so this is causing Duchene muscular dystrophy becker is usually due to what's called a missense mutation where you're just substituting an amino acid and for another one and it changes the overall shape and if you know there's what's called the complementarity concept that structure complements function so whenever the protein shape is changed from its normal structure to an abnormal structure it changes the function so in Becker's it's due to a miss folded protein so we say a miss folded protein because it's caused by a missense mutation so this is caused by a miss folded protein now you guys are probably wondering okay well you told me all about muscular dystrophy how does that how does it actually happen well imagine here this is anchoring this whole structure to the actual this actual cell membrane if this protein isn't present or it isn't functional what's going to happen to this now now this membrane is going to sag down if this membrane starts sagging down because it doesn't have this dystrophin to hold it stabilizing steady and maintain the cytoskeletal structure again what will happen this membrane will sag down over time the membrane will start to break down as the membrane starts to break down proteins and enzymes an ion step moving in and out of this actual cell and eventually the muscle cell becomes fibrous and fatty so in other words the muscle cells die they get replaced with fibrous tissue and fatty tissue and they don't function so what would eventually happen to people with muscular dystrophy they have muscle weakness and this muscle weakness can get so bad because one of the main skeletal muscles is called our diaphragm the diaphragm is responsible for helping us to breathe and inhale so if this muscle was actually damaged or became progressively weak they would develop respiratory failure another thing they'd have a hard time being able to move they usually have a strained waddling gait right and it's because they don't have very very strong hips right so usually the muscles of the hips are very weak another thing that can also be a problem with this months to the dystrophy is eventually if it can affect the heart muscle because dystrophin is not only present in the skeletal muscle but it's also present in the heart muscle so it can cause belly actual the muscles the actual car muscle to become very very dilated and very floppy and flabby and that's called dilated cardiomyopathy so usually the individuals there's not much treatment for these individuals they have to get you know physical therapy to try to improve the quality of life sometimes they can get glucocorticoid they're people there's a lot of side effects and sometimes they're actually working on stem cell therapy also but not much success so far in that unfortunately but it just goes to show you these proteins they play such a huge role something so small can play such a big big role in our entire body's physiology okay so that pretty much guys covers a lot of information here about our actual myofibrils consisting of our sarcomere a bands or eye bands we'll talk about this again will actually recap this even more whenever we go into the actual excitation contraction coupling guys I really hope you guys enjoyed this video I hope it made sense thanks for sticking in there with me and it was a long video I hope you guys really did enjoy if you did please hit the like button subscribe put some comments down in the comment section alright engineer until next time