all right ninja nerds in this video we are going to talk about the development of the muscular system primarily focusing on the skeletal muscle system before we get started please hit that like button comment on the comment section and please subscribe also tell others that you know about this channel bring them in so we can help them learn as well if you guys want to support us down in the description box we have links to our facebook instagram patreon go check that out if you guys can donate we truly appreciate it all right engineers let's get into it all right ninja nerds let's start talking about the development of the muscular system now what i want you guys to do if you guys haven't already please go watch the development of the skeletal system because the path that we're going to take in this video is the exact same first thing that we got to do is we got to start talking about the muscles of the face right of the head and neck area then after that i want to start talking about the muscles of the trunk then after that i want to talk about the muscles of the limb so we're following the exact same path of the development of the skeletal system all we're doing now is putting some muscles over them bones that's all we're doing all right so let's start with the development of some of the head and muscles like super hyoid muscles how does that happen well here we have our embryo and what kind of section are we looking at you guys are going to get real good at this stuff right so we're going to keep reminding you what is this edge here right that's our buccal pharyngeal membrane this is our cloacal membrane this is a what kind of section this is our sagittal section it's our sagittal section and so which end is cranial this is your cranial end near that buccopharyngeal membrane and this is the caudal end near that coal membrane right what i want us to do is to take a section at a particular part near that buccal pharyngeal membrane what we're going to do is we're going to cut through this son of a gun right like this we're going to cut through there through that primitive pharynx and we're going to zoom in on it and look at it this is what we're getting we're getting this view of our primitive pharynx if you will so we're getting this view of that primitive pharynx and what i want you to understand is the different layers of this primitive pharynx so what happens here is what is this membrane this is the first thing i want you guys to know we already kind of talked about it up there where's my marker here it is this membrane right here where you have the fusing of the ectoderm in blue and endoderm and green what is this called this is called jor bucco pharyngeal membrane all right so that's that point there where there's a fusing of what two tissues what two parts of the germ layers the ectoderm and the endoderm then again you have the ectoderm kind of lining out here forming kind of this like ectodermal lining here and mesodermal lining here and then endodermal lining there okay so green endoderm blue ectoderm and red mesoderm what happens is that this primitive pharynx starts kind of undergoing this vesiculation process so it's that it kind of starts forming these like little vesiculations and look what happens when it kind of forms these little vesticulations it forms this very special type of pharyngeal apparatus if you will now when you look at this pharyngeal apparatus you have this portion here which is kind of like your arches right so you have these pharyngeal arches which are kind of going from side one end here to this end here and filled in the core of that arch is mesoderm on the outer part of it is the ectoderm and on the inner inner part of it is the endoderm so this whole thing is a pharyngeal arch what happens is the mesoderm within the first second third fourth and six pharyngeal arches actually undergo a differentiation process to make muscles of the head and neck particularly at the suprahyoid region generally so what are these pharyngeal arches that is the important thing to know so this first chunk right here what is this one this is called your first pharyngeal arch all right so we're going to put pharyngeal arch here these are pretty common sense right this one's your second pharyngeal arch so second pharyngeal arch here this one is your third pharyngeal arch now here's where it gets a little interesting you have your fourth and you're like whoa what happened to the fifth i go fourth and sixth that's interesting the reason why is you have a fifth but generally it kind of degresses and actually disappears and so generally at the end here whenever you're forming a pharyngeal apparatus you really only have a fourth and a sixth the fifth digresses so now we're going to have the fourth and the sixth pharyngeal arch now what i want you to know is that this mesodermal cores here they actually are going to be the parts that form some of the muscles but there's also going to be nerves that are going to supply the muscles that are derived from these arches what are those nerves and that's what's really important because if you remember the nerve you'll remember the muscles the first pharyngeal arch is going to supply the muscles it's going to become the muscles of mastication a couple other ones as well but the reason why i mentioned the muscles of mastication is you guys can remember what nerve supplies that that is cranial nerve five what is cranial nerve five the trigeminal nerve the second pharyngeal arch is going to be primarily making muscles of facial expression and there is other muscles but again that's the big one because that's supplied by cranial nerve seven the third pharyngeal arch is one muscle called the stylopharyngeus but that is going to be supplied by what the glossopharyngeal nerve which is going to be cranial nerve nine and the fourth and sixth fringe arch makes actually muscles of the larynx the pharynx and another muscle called the levator v lipolytheny and that is supplied by what cranial nerve ten which is the vagus nerve so what i want you to remember is the muscles of the head and suprahyoid muscles are derived from the what portion the pharyngeal arches which come from the primitive pharynx if you take a cut here at this level you have their primitive pharynx you have your mesoderm they undergo this kind of vesiculation process where they make this core of mesoderm forming these arches these arches will become muscles but i want you to remember the muscles are supplied by particular cranial nerves next question that we have to answer is what do these mesodermal cores become what muscles do they become within these arches let's do that now all right so the muscles that are actually going to be derived from the frontal arches again what is that it's going to be your head and kind of like super hyoid region right so the first pharyngeal arch we said is supply by cranial nerve 5. so what from this portion it's going to go make muscles of a part of our face these are going to be your muscles of mastication if you guys want to know them i'll tell you them i'm not going to write them down but it's the temporalis the masseter and your pterygoids you've got your lateral pterygoids and your medial pteroids but those are going to be muscles that help and again are making part of our face the other one here is there's what's called the mylo hyoid okay so this is your mylo hyoid again this is one of your suprahyoid muscles remember i told you these are going to be muscles of your neck but particularly suprahyoid there's also going to be the digastric so your digastric and particularly what's called the anterior belly of the digastric and the last one is going to be what's called your tensor v-li palatini or palatini however you like it but again these are muscles that are going to be derived from the french arches the second pharyngeal arch okay so first was by cranial nerve five supplied all these muscles by cranial nerve five second is by facial so remember i told you the best one to remember is the muscles of facial expression i am not going to go through this because there's like a ton of these okay but all most of the muscles of our face right most of the muscles of our face are actually muscles of facial expression supplied by cranial nerve five a couple other ones again you get the super high muscles right what else do we have we have another one which is going to be called the stylohyoid so it's called your stylohyoid and another one is called your digastric posterior belly there is a small little other one called the stapedius muscle don't worry about that one though okay all right the next one third fringe arch supplied by the glossopharyngeal nerve this is a tiny little muscle that's going to help with the formation of muscles of the soft palate this is called your stylo pharyngeus stylopharyngeus okay and then the last one is the fourth and sixth pharyngeal arch muscles which are going to be supplied by the vagus nerve this is going to be a small little muscle that's again near the actual uh soft palate it's called the levator v-li palatinai or the palatini okay and then the other muscles they're a group of muscles you have what's called your pharyngeal constrictor muscles so some of the pharyngeal muscles and if you guys remember that there's the superior middle and inferior pharyngeal constrictor muscles and then the last one is your laryngeal muscles all right so all those uh arytenoids the cricoarytenoids the cricothyroid muscles all those sons of guns are actually going to be derived from these arches now if you guys remember we talked about how we make the skull right we make the neurocranium and the visceral cranium all those bones and cartilage and all that stuff what are we covering all that with now the muscle so you see how it's kind of layering there so now we have all the muscles of the head and muscles of the neck but what part suprahyoid okay that's going to be from our pharyngeal arches now let's go ahead and talk about some of the muscles that are infrahyoid right hitting some of those like strap muscles and then going into the trunk all right so we talked about the development of the muscles of kind of the head and neck but just above the highway bone now let's go ahead and just keep going let's talk about all the rest of the muscles really from this point so let's start talking about some of the muscles of the trunk and the girdles okay so particularly the pectoral girdle and then the pelvic girdle and then again we'll talk about some of these inferior hyoid muscles and some of the strap muscles as well all right so first thing that i want you to know is when we start talking about these truncal muscles we have to go back to our kind of embryo looking at this thing here right so you're going to see this kind of format a lot so again what is this layer here this is our ectoderm right this kind of blue layer all the way around and then again if you come back here what was this actual tissue here this part of the mesoderm closest to the neural tube so here's your neural tube right here this one is called your par axial mesoderm do you guys remember what this chunk of mesoderm does on the sides of the neural tube it starts forming somites right remember that then if you go a little bit lateral to that you have the intermediate mesoderm right our intermediate mesoderm and then the last one is you have these two layers here which is going to be called your so you have this one here and then this one here this is actually going to make what this will make your lateral plate mesoderm so your lateral plate mesoderm okay and then again you have two layers flank thick layer and somatic layer good what i want us to do now is start talking about the muscles of the trunk so what i want us to do is take this neural tube and these actual paraxial mesoderm chunks and just yank this out here and just zoom in only on that neural tube and on the par axial music on the sides of it let's just focus on that portion so really i only want us to look right here okay so here we have our neural tube here we have our notochord and on the sides what do we have let's actually abbreviate it this is our par axial mesoderm par axial mesoderm here's our neural tube and then this is our notochord that black dot there right remember what happens to the actual par axial mesoderm what do we say it undergoes the somite formation right so somites are these little chunks right so if you imagine here imagine here you had a neural tube okay what happens is you have these actual paraxial mesoderm chunks on the side what they start doing is they start actually kind of like forming from a cranial so let's say here's cranial and and here's your caudal end these start forming about three of them per day and you generally get about 44 to 45 of these by week five but these kind of like little chunks of mesoderm are called jor somites and they're going to form on the sides of your neural tube what happens is if we look at just one of these actual somites you form a little space in it this little space in it is called a somatoseal so this is a somite but it becomes again having a little space in it it has what's called a somato seal and again this is called a somite and again there's about 44 to 45 of these sons of guns that go and actually form from cranial to caudal fashion about three per day now what happens is this somite has a somatoseal that continues to keep expanding and as it continues to keep expanding it actually kind of cuts the somite into two portions one is this dorsal portion back here right because here's our neural tube here's our notochord this is the dorsal portion this is going to be what's called the dermatomyotome and then this ventral portion here is going to be called the sclerotome what happens is the dermatomyotome differentiates even more it cuts up into two pieces now you have this most dorsal portion here called the dermatotome i'm sorry dermatome and then you have the next middle layer here called your myotome and then you have the most inner layer of the ventral layer here which is called your scleratome but we're going to go another we're going to go one more now i'm going to have another layer form between the myotone so again what is this one here most dorsal is your dermatome think about this in superficial to deep is the easiest way to remember it what do you have obviously you have epidermis so if you really wanted to think about it obviously right here you would have ectoderm that's going to make your epidermis right so this would make your epidermis what's underneath your epidermis your dermis that's your dermatome what's underneath the actual dermis your myotome your muscle what connects so what's your uh this most inner layer here we said this one this was the scleratone what do we say sclerotine makes bones cartilage stuff like that right what connects bones to muscle tendons here this most kind of like intermediate layer between the myotome and the scleratome is called your cinder tone your cinder tomb is going to be what makes your tendons so we took this par axial mesoderm and from that made how many layers from superficial to deep if you'd like to think about it or from dorsal to ventral dermatome myotomecin to toms clariton beautiful now what i want to do is in an orderly fashion recap you guys guys memory go from the scleratome all the way to the dermatome primarily focusing on the myotone and senditum along the way all right so let's recap you guys memory what do we say happens with the scleratone we know it goes through that whole resegmentation process to form inter vertebral spaces for the spinal nerves to run through but what happens is remember the scleratome starts kind of wrapping around the neural tube and what does it do forms the vertebral body the vertebral arches the spinous processes the transverse processes and the ribs so now what do we got come down here look from this our scleratome is now gone we're going to kind of delete things as we go why because what does it become we already talked about this in the development of the skeletal system it's going to become in short your vertebrae right and we already talked about the vertebral arches spinous transverse processes and body it's also going to become the intervertebral disc we're going to abbreviate this intervertebral discs and it's going to become the ribs which start off as the costal processes and then become the ribs right now that's the first thing now let's do the next layer so we're going to abbreviate these just with the letter right so this is your dermatome myotome cinditone okay let's put y here just so that we don't confuse with the sclerotime so again dermatome myotomed centitone now let's take this next thing and take the cinder tome and start making tendons that are going to connect bone to the next layer myotome so now look if we follow this over here now the cindatoma is going to form into tendons so if we look here we're going to have our bones right so here's going to be our vertebrae here's going to be the ribs look what we started doing the cinder tone is now going to make all of this tendons and we're just going to kind of put tendons here and we're going to put some tendons here right along the ribs along the vertebral bodies all that stuff like that because that's going to be an attachment for muscles so now what did we do here we formed tendons and again why are tendons important because what do tendons connect they connect muscle to bone here's our bone what's the next layer before we go through that i need you to remember something again what was this layer here dermatome what was this layer here myotome now i want us to now cut this myotome in half let's do it with this blue marker i'm going to cut this in half and on one half here in pink this part here is going to be the dorsal and more medial portion of that myotone and then in green here you're going to have this more ventral and lateral aspect of the myotome why am i stressing on this why am i harping on this here's why the we take a chunk here okay and again we're going to draw a line down the middle here and let's say that this is going to be again dorsal medial ventral lateral color coordinate here green for that ventral ventrilateral portion here and then pink for this dorsal media portion here this dorsal medial portion is going to just only move into the muscles around the back so this is only going to form the muscles of the back we'll talk about this in a little bit but this is going to make what's called your ep axial muscles epi axial muscles and then this ventral lateral portion of the myotome is going to form what's called the hype axial muscles now i'll explain what that means in a second but again what i want you to think about here is in the form of migration this portion here is going to move all right here and then these ones are going to move out here to where the actual ribs are and then out into the limbs okay so that is really important for you guys to remember so again when we talk about the myotome the ventral lateral layer is going to go out and make hype axial muscles and the dorsal medial layer is going to just move dorsally and form the epiaxial muscles now let's take that now let's go to the next step remove the myotome form those muscles of axial and hypoxial muscles on the next diagram let's come up all right so now let's take a look here okay we got rid of the actual myotome right and the myotome did what it formed epi axial muscles which are gonna be these muscles right here so you see how this chunk of muscle here we're gonna have the dermatome here in a second but here this whole thing here is gonna be what's called your epi axial muscles we'll talk about what these are but these are gonna be the muscles that form the muscles of the back okay then you're going to have these other muscles called the hype axial muscles and the hype axial muscles are going to be the ones that form the muscles of the trunk and will even invade into the limbs and make the limbs the muscles of the limbs we'll talk about that in a second but again we had the uh cinder tone form the tendons the myotome formed the ep axial muscles so the muscles here around the vertebrae and then the high bacterial muscles which are around the ribs right and will go out into the limbs now let's just kind of for simplicity's sake here what do we have as a layer above this just we'll do a different color so we don't confuse here what was this layer that was remaining this is the dermatome right the dermatome is going to do what invade this area and what is that going to become the dermis which is this kind of red layer here and the green which is the subcutaneous tissue so if we got rid of that one so again here's going to be the myotome forming these epi axial muscles hypoxial muscles and what i'm going to do is just so you understand what happened to the dermatome we're now going to take that dermatome and move that where it's going to move outwards underneath the ectoderm and make what tissues here it's going to make the dermis and it's going to make the subcu cool right and then what's the ectoderm going to make the epidermis so we see how we make the muscles of our trunk whether it be the back or the ventral lateral portion here let's now kind of refine what ep axial muscles and hypaxial muscles are okay so we talk about the epi axial muscles these were the ones that were formed by what portion the dorsal medial portion of the myotome these are making muscles of the back so i want you to remember back muscles okay so i want you to remember the back muscles so if you wanted some of these remember like your erector spinae so these are going to become some of the muscles called the erector spinae these will become some of the really deep muscles within the spine called the multifidi multifidi and then you also have another one called the rotaries you'll also have some other muscles which are going to be towards like the top like your semi-spinalis spinalis capitus and then if you really want to go the extra mile you even have some of those sub-occipital muscles so those recto rectus muscles and then the obliqus muscles there so you even have some of that those sub-occipital muscles as well okay so these are going to be forming basically the muscles that are surrounding the vertebrae all the way from the actual base of the skull down until you get to that actual pelvic girdle pretty cool right the hype axial muscles what do we say that was the ventral lateral portion that moved outwards and formed some of the muscles around the ribs which are part of the trunk and then even even did what moved out into the limbs we'll talk about that in the next section but if you think about the hype axial muscles i want you to remember trunk but particularly what portion the ventral on the lateral trunk because the back is pretty much the dorsal trunk if you want to think about it like that right so what are some of the muscles that surround your ribs pretty straightforward right what is the muscle that connects to the ribs and pretty much controls your breathing your diaphragm right so your diaphragm the only way i can spell it right so your diaphragm the other ones is your intercostal muscles your external internal intercostal muscles so your intercostals those are some other bad boys there right right and your serratus your serratus anterior and posterior they connect to the ribs right so your serratus muscles and then your abdominal muscles okay your abdominal muscles those are also going to be derived from the hype axial version right so your abdominal muscles what are some of those your transversus abdominis your internal external obliques all those are derived from the high back seal portion and then again what we're going to talk about next is the limbs your upper limbs right pretty straightforward but might as well write it in the lower lips okay so so far we've talked about the development of the epi axial portion and the hype axial portion which is all coming from what aspect of the mesoderm the par axial mesoderm what component of the par axial mesoderm the myotome epi axial from the dorsal medial uh hype axial from the ventral lateral so now we've talked about the muscles of the head we talked about the muscles of the suprahyoid add-on just a teensy bit more because i want to just mix that we also don't confuse high back seal muscles a couple other ones that you could add into this to kind of fill the gaps here is we said what was remaining that we didn't cover in the head and neck infrahyoid so the hypaxia muscles also cover some of those infra hive muscles and some of those strap muscles sternocleidomastoid the scalene muscles all those guys there and then the muscles uh basically around your girdles are going to be coming from this actual hypoaxial muscles and we'll talk about there's a teensy bit when we get into the limbs so we now know how we form the muscles of the head neck and trunk let's hit it hard with the limbs all right so we've talked about the trunk we hit the head and we hit the neck all right so pretty much if you think about it hit all the axial musculature now let's hit the appendicular musculature so it's kind of going back to that skeletal system if you guys remember we had to kind of form the limb buds and we're not going to go through all this too much i just want you to remember what were those genes involved in the limb buds your hox genes your tbx4 your tbx5 genes and there's going to be other things like your fibroblast growth factor that has to be produced as well type 10. so all of these genes need to be activated in order for these limb buds to find their proper position as well as for them to initiate and induce this process of limb blood formation now if you guys i don't know if we talked about this in the skeletal system one but the limb buds generally derive around c5 to t1 region and then l2 to about s3 region is where your limb buds form so upper limb bud we're going to abbreviate in lower limb buds okay so if you guys remember okay from the development of the skeletal system we have our limb bud here do you guys remember that at the edge of the limb bud what did we have kind of coming out here this is all ectoderm all this blue is ectoderm but at the tip of this ectoderm this limb blood we had what's called the apical ectodermal ridge this was an area that was releasing a lot of fibroblast growth factors and triggering the lateral plate mesoderm do you guys remember what happened with that lateral plate mesoderm the lateral plate mesoderm invaded which portion remember this was the splanchnic somatic the somatic layer of the lateral plate mesoderm invaded this limb but and that apical ectodermal ridge was stimulating this to proliferate proliferate proliferate and form what's called that progress zone and then this the mesoderm that was far away from the epiglottic merge underwent differentiation and made bone eventually right so we already covered that so now what i want us to do is just take this portion of the limb but we're just going to take this upper limb bud and zoom in on it and now actually that we've already formed the bones and we've already talked about that now let's lay on our layers here okay so focusing in on this limb we've already had our apocalypto derma ridge drive the proximal to distal formation we've already had the zona polarizing activity guide the anterior to posterior development and then you have that ventral and dorsal ectoderm that grind the dorsal ventral surfaces boom now that we have our bones laid down okay what did that come from let's remember i don't want you guys to forget the layers what did the bones and cartilage come from that came from this layer what was this layer here called we're going to abbreviate lateral plate mesoderm and this was which part of the ladder plate mesoderm this was the somatic layer that formed the bones and cartilage of the limb then come back here let's abbreviate these dermatome was the most dorsal myotome then you had jor cindatom so dermatome myotome cinditome and then what was this one let's put sy and then sc for sclerotome we don't need the sclerotome because that formed the vertebrae the ribs all that stuff there what do we need next we've already formed the bones that came from the lateral plate mesoderm now what i need to do is i need to lay down a particular tissue that connects bones to muscle what did that come from the cinder tone so now what i need is i need the synditome layer to start migrating and move into this actual limb bud and when it does that guess what this actual cinder tome does so this is going to be what happens in this step the cinder tome migrates so the mesenchymal cells from the actual cinder tome migrate into the limb blood and what do we say the cinder tone makes tendons so now we laid our bony layer here first with the lateral plate mesoderm somatic layer now what have we laid down next our tendons and we did that with the cinder tome coming from the par axial mesoderm so again what is this orange stuff here tendons now that we've laid the tendons down what's the next layer to start feeding in here the next layer is this one so we hit the cindertome now we've got to hit this one which is our myotome so what happens is this myotome starts migrating and it migrates into this portion here into this portion here and once this myotome migrates in here we have this myotome migration so what now just happened we had cindertone migration now we're having myotone migration myotome migration this does something very interesting when the myotome migrates into this let's think about this thumb here and then the pinky here okay generally when you're developing okay in the embryo the thumbs are anterior okay so the thumbs would be anterior and the pinkies would be posterior so there's a reason why i'm telling you that the myotone migrates into this kind of anterior portion and migrates into this posterior portion and when it does it just forms kind of chunks of muscles non-specific it's just a chunk of muscle on the anterior portion and a chunk of muscle on the posterior portion in this limb bud we call this chunk of muscle in the anterior portion of the limb bud the anterior condensation and then we call this chunk of muscles that are actually from the myotome migration and the posterior aspect i know you guessed it the posterior condensation that is important because eventually we'll talk about in a second the anterior condensation will do what will form particular muscles they'll actually start differentiating and really becoming more specialized and become muscles that are very specific in the arm or legs the last thing i want to make sure that you guys know is we've covered an order lateral plate mesoderm somatic layer made the bones and cartilage the cindatone made the the actual tendons the myotome made the anterior condensation and posterior condensation what will the dermatome do it will make the [Music] dermis and subcutaneous tissue that will go all around this area here right so that's pretty straightforward now let's talk about what this anterior and posterior condensation are a little bit more all right so we talked about how these muscles the myotome invades the limb bud right and forms this anterior posterior condensation i want us to dig just a little bit more into that and kind of elaborate more on that there's a reason why because they're embryologically derived to be functionally different in the upper and lower limbs right so let's say here we talk about the upper limb right so the anterior condensation of the upper limb and then the anterior condensation of the lower limb and let's just be simplistic let's think about it logically myotome invades into the upper limb all the muscles let's start here let's start here at the actual upper arm what does these muscles do they flex they flex at the elbow what do these muscles do they flex there's another group of muscles right here what do they do they help with pronation pronation so the anterior condensation for the upper limb will make what kind of muscles flexors and what else pronators for the uh the next aspect here for the lower limb think about it keep it just simple if you move here your quads what are they doing they're playing a role in extension what is the actual muscles of your lower leg doing they're playing a role in what kind of aspect here dorsiflexion and then on the inner aspect what do you have in here your adductors so if you think about just anterior compartment that makes it pretty simple here where you have extensors it's also going to make what's called adductors this is kind of for the upper aspect of the lower limb and then the most lower leg portion will be your dorsiflexors pretty cool right how the embryologically they lead to functional differences and and the adult i think that's pretty cool from ninja to nerd make sure that you guys comment how cool is this all right all right next thing all right so now the posterior condensation same concept here you got your upper limb okay so these myotome uh migration into the uh upper limb will produce different types of muscle function and then lower limb same concept here think about this upper limb you got the muscles invading all this posterior portion here triceps what are they doing they're extending and then you also are going to have these muscles which are going to extend like your wrist and digits but then you have some really deep muscles that help with being able to kind of do this kind of motion called supination so with your upper limb the posterior condensation plays around what's called supination and it's also going to help with the muscles that are going to be functional for extension and then when you think about the muscles of the lower limb and the back the hammies what are those going to be doing flexing okay so they play a role with flexion at the knee and then you have the muscles of the calf those are important for plantar flexion right so they play a role in plantar flexion and then don't forget about those muscles that go around the outside right that are going to be kind of the gluteus some of those deep muscles those are also going to be helpful for abduction okay so abduction that is why i really wanted you guys to understand is not to just know the muscles of the limbs but to know how embryologically they lead to functional differences in the adult and and even in the child so that's pretty darn cool all right so we talked about this for bone formation i want to kind of cover the same concept with muscles so remember what we pretty much derived all the muscles from mesoderm right whether it was par axial whether it was lateral plate mesoderm or whether it was from the mesoderm from the um pharyngeal arches all of it for the most part was mesoderm well mesoderm again goes from epithelial cells to mesenchymal cells it's called epithelial to mesenchymal kind of like transition and these mesenchymal cells are mesenchymal cells however you like to call them they have to start kind of differentiating right and becoming particular types of cells that are destined to become muscles and these are called your myoblasts your myoblast and then eventually what happens is your myoblasts will start fusing together you'll get these myoblasts and they'll fuse together and they'll form like these muscle fibers okay they'll form these muscle fibers and then what happens is a bunch of muscle fibers you see how you have nucleated single nucleated cells these muscle fibers fuse with more muscle fibers and eventually you just get a big chunk of muscle right in order for us to go from these mesenchymal cells or mesenchymal cells to this actual muscle cell differentiation we need particular genes to be activated for us to differentiate have this different phenotype and these genes let's say that are involved in this process are very specific actually so generally the first genes that become activated for kind of leading to these muscle differentiation are called your pax genes so these pax genes need to be activated but pax genes will then activate another set of genes they'll activate genes that are called myo d and another one called myf okay and there's like four and five and then these genes will become activated and they'll lead to the activation of what's called myogenin and myogenin is what really gives that different muscle cell difference and why is muscle cells different well they have different proteins actin myosin troponin tropomyosin all of that is dependent upon this gene activation and differentiation process so again we know that when we go from mesenchymal cells to muscle cells we have to activate certain types of genes to lead to those particular muscle proteins to be expressed and be phenotypically different all right so that covers everything we need to know about the development of the muscular system all right engineers so in this video we covered the development of the muscular system i hope it made sense and i really hope that you guys enjoyed it if you guys did please continue to support us in any way that you can niche nerds we love you we thank you and as always until next time [Music] you