hello everyone and welcome back to my playlist of system based embryology today we are going to start chapter number 11 which is dealing with the development of muscular system so you know in the body we have got three basic types of muscles these are skeletal muscles smooth muscles and the cardiac muscles okay or uh we are going to discuss muscle types with the exception of some smooth muscle tissues the muscular system develops from mesodermal germ layer so uh almost all of the muscles develop basically from the mesoderm there are few exceptions the muscles are not actually developed from the mesoderm they are rather developed from the ectober key exceptions primarily muscles they include muscles of the iris uh people may uh jopipolini Constructor or dielectric muscles the iris muscles they are made from ectoderm and also muscles present within the sweat glands and also the muscles present within the mammary glands so these are the exceptions to the rule these are three examples which are not formed from mesoderm but rather they are formed from ectoderm or the examiners muscles are made from but yeah there are some muscles which are actually made from ectoderm okay with some exceptions and they consist of skeletal muscle smooth muscles and foreign this is one terminology that you should know then there is a terminology which is called visceral and parietal mesoderm layers so these terminologies we have discussed already in the embryonic period like because if you don't understand these terminologies you are not going to understand the rest of the chapter is chapter six this is the embryonic period time is the developing embryo and this is the notochord is this is the midline of the embryo in notochord and this is the neural tube okay neural tube so if you look at this diagram this black thing is the notochord and here these are the neural force or you have a neural tube so that's the central area of the embryo is Central midline area and this is known as paroxys videos which is on both sides of the midline muscles literally so that area is known as the lateral plate mizoram so mizoram basically is divided into the par axial mesoderm which is this thickened portion and then the thin portion which is called the literal plate mesoderm or Jason is a development process what happens if you look at this diagram so e again midline here this is the midline is the par axial mesoderm which develops into somite or due to literal plate mesodium it is now split which is towards the amniotic cavity so this is the amniotic cavity this here is the amniotic cavity lateral plate mesodrome layer is covering the amniotic cavity and this layer of mesoterm is known as uh that is called parietal mesoderm layer okay so this is the parietal mesoderm or mesodrome this layer this is known as visceral mesodrome you should be very clear about what is par axial mesoderm the parietal layer of mesoderm and the visceral layer of mesoderm so both these are basically from the lateral plate mesoderm or midline that is with this concept let us now study skeletal muscles they are derived from the peroxide from the occipital region of the embryo to the sacral region of the embryo and these somites make not only the muscles but they also make the drama charms they also make the skeletal system smooth muscles your hand they differentiate from the visceral uh visceral yes surrounding the gut region and its derivatives and some muscles also develop from the ectoderm such as the pupillary muscles muscles and sweat glandular muscle so these are exception they are made from ectogen muscle hair that is largely made from the mizorami different parts they are derived from the visual so all the somites are developed from the par axial mesoderm in the head okay musculation of the axial skeleton body wall and limbs is derived from somites which initially forms somebody to mirrors and extends from the occipital region to the tailbird immediately after segmentation these tomato mirrors undergo a process of epithelialization and form a ball of epithelial cells with a small cavity in the center so basically is it starts forming structures lateral to the midline and these structures are called somites and these somites then ultimately develop a cavity in this somite uh ultimately forms all the structures which are a basic component of the body wall the limbs and these structures include muscles bones as well as Ramadan diagram so this is again the notochord so this is going to be the midline of the body or its midline this is the neural fold so you have a neural tube a midline this mesoderm is the paroxyl mesoderm and now The Spar axial mesoderm has been developing into somite so this is now developing into a somatic structure further development is but the point is this the par axial mesoderm is converted into somalitomeres and then the somato mirrors are converted into mature somites or in mature so might same skeletal muscles one thing so the skeletal muscles they are being formed via somites which are formed by the paraxial mesoderm is that clear okay now the ventral region of each somite becomes is sclerotom the bone forming part of the somite cells in the upper region of the summit from the dermatom and there are two muscle forming areas which are called ventraliteral and dorsomedial lips or the edges no cells from these two areas migrate and proliferate to form the progenitor muscle cells ventral to the dermatom thereby the Derma myotrom is formed now what's actually happening and it divides into a dermatron structure so a structure is but now it is differentiated to form a dermatome and uh this will form the bone egg Corner uh foreign region also migrate to the adjacent parietal layer of the lateral plate mesoderms yes what is the parietal layer of the lateral plate meso drum now if you again look at this diagram let's start from this one let me rub it so that I make some more space for you to understand this clearly so this is the literal this is the power axial mesoderm paragraph literally this is the lateral blade misograms this is known as the parietal layer okay they migrate towards the parietal layer or your parietal layers they start forming infra hyoid muscle abdominal wall muscles such as rectus abdominis internal and external oblique limb muscles the remaining cells in the myotome form the muscles of the back shoulder So This Is How They are forming all the skeletal muscles you know of the abdominal wall of the limbs of the shoulder girdle of the intercostal area or muscles of the back they are all formed from either the ventral lateral or the dorsal medial type of cells okay actually initially there is a well-defined border between each somite and the parietal layer of the lateral plate mesoderm and this clear-cuts division line is known as lateral somatic Frontier there is actually a clear-cut boundary type of structure is all this is the somite areas let me do it again one more time so that is all the somite area is the lateral plate mesoderm this boundary is actually known as a lateral someric Frontier okay so actually both important Landmark here is you have to remember this lateral somatic Frontier now this Frontier separates the two mesodermal domains in the embryo uh one is called the prime axial domain that comprise the region around the neural tube and contains only somite derived cells is all this is known as primaxial domain and abaxial domain that consists of the parietal layer of the lateral plate mesoderm together with so much cells that have migrated across the lateral somatic Frontier up is boundary key is somatic cells and medial to this boundary is the primex ZL domain Prime axial domain and ebaxial domain or in key differentiating line here a border between the somite and the lateral plate misograms is muscle cells that cross this Frontier and enter the later plate mesoderm comprise the ebaxial muscle okay and those that remain in the paraxial mesoderm and do not cross the frontier are known as the primaxial muscle cell so this area will be the primaxial area this area will be the abaxial area Okay so yeah terminology regardless of their domains each myotome receive its innervation from spinal nerve derived from the same segment as the muscle cell a simple rule here segment so that's a general principle of embryology throughout the body now the lateral somatic Frontier a terminology Frontier literal somatic Frontier it's the boundary between the somite and the lateral plate mesoderm so lateral somatic Frontier also defines the border between the dermis derived from the dermatome in the black and dermis drive from the little plate Museum in the body wall so little blade is important for many reasons it also defines a border for rape development such that cells and the cartilaginous part of the ribs are actually derived from the uh you know those cells which have migrated towards the lateral plate Museum so primaxial is that will form the cartilaginous part of the rib so this is an important Landmark I told you it's Landmark development rules and principles and principles there are all the lateral plate mesoderm derivatives and also some cells okay let's move on and start talking about the innervation of the axial skeletal muscles Now new description of the muscle development description there was a boundary line or okay this is the recent Advance this is a recent development is defined here it was rather known as the Epi mirrors and the hypomares epimeres were supposed to give origin to the back muscles and hypomares were supposed to give origin to the limb and body wall muscles uh I'd say I mean a decade ago that was the concept but this this has now changed okay epimeric muscles were innervated by the dorsal primary ramay and hypopanic muscles were innervated by the ventral primary muscles they were innovated with the dorsal primary muscles and they are all you know innervated by the dorsal primary Rama Sunny Anatomy change over here embryology they are made from the primaxial and the ebaxial domains okay now the new description is based on the actual embryological origin of the muscles uh from two different types of cell populations the ebaxial and the primaxial cells and not their innervations Anatomy Remains the Same okay get your back muscles here they are actually he is still inner rated by the dorsal primary Mi or your front muscles and body Volcan they are still innervated by the ventral primary Ramis so this has not actually changed okay now skeletal muscles and their tendons during the differentiation precursor cells the myoblast fuse and form long multi-nuclear now this is is where we don't know actually how it is done and what is done there will be so much there will be some light formation so might can say myotome area myogenic cells cellular proteins but this is what happens never segregated this is actually all the details which is very vague they start developing into elastic fibrous tissue that ultimately forms the tendon the transcription factor is clear rexes regulates the development of tendons I mean this is one of the factor that we know to date there are only some genes that we know work in a way some molecular regulation of the muscle development now genes regulating muscle development have recently been identified I would say only I mean a few of the genes have been identified I'm sure it's not about sari jeans okay now bone marfo generic protein 4 bmp4 and probably fibroblast growth factors from the lateral plate mesodrome together with the wind proteins from the adjacent ectoderm signal the ventral lateral cells of the dermatomyoton to express the muscle specific Gene now myod is a gene which is activated in the areas where muscles have to be formed expression um muscle forming regions no reasons it is controlled and initiated by a lot of factors for salesman now bmp4 secreted by the actor normal cells control actually induces the production of wind proteins by the dorsal uh neural tube at the time that low concentrations of Sonic Hedgehog proteins are there and basically Joe dorsomedial cells of the terms of Sonic Hedgehog key expression so that is the sort of story okay both mayori and MI5 are members of a family of transcription factors called myogenic regulatory factors these are both the genetic areas in the genome which if expressed will make muscle cells okay so that's the bottom line so this diagram kind of tries to summarize different areas that sort of thing okay this is what is known to date now patterning of muscles patterning of it's a very generalized concept of embryology human development single cellular Mass responsible it's always the interaction between various cell types is a group of cells these are the cells name muscle cells May develop so these cells are basically precursors of muscle cells okay these are all derived from mesoderm we know this is genetic Expressions between the neighboring cell types and the differentiating cells this is what is known as pet running other patterns of the muscle formation are controlled by the connective tissue into which the myoblasts migrate the energy myoblasts connective tissue environment May proliferate those environmental factors control its uh you know positioning its development its differentiation is patterning for example in the head region the connective tissue are derived from the neural crest cell in a head region May somites muscles by the cells of the neural crest cells embryology it is the interaction of the cells which lead to development of any structure okay in the cervical in the occipital region they differentiate from the somatic mesoderm and in the body wall and the limbs they originate from the parietal layer of the lateral plate so that's what of a general paragraph This is now the head musculature all voluntary muscles of the head region are derived from the paraxial mesoderm by the formation of the somites including the musculature of the tongue musculature of the eye and except for the iris you know that iris is formed by the ectoderm okay and that associated with the pharyngeal Arches patterns of the muscle formation in the head are directed by the connective tissue element derived from the neural crest so head gender muscles differentiation control or guide by the neural crest cells limb musculature the first indication of the limb Mass upper limit lower limited muscles is observed in the seventh week of development as a condensation of the mesenchyme near the base of the limbers foreign and it starts forming the muscles in the limb region okay as in the other region the connective tissue dictates the pattern of the muscle formation yeah and this tissue is derived from the parietal layer of the lateral plate mesoderm so you're dictating uh tissue hair that is from the lateral plate mesoderm so milky somites or connective tissue muscles right now the development of the cardiac muscle cardiac muscles develop from skin cell types they develop from the visceral mesoderm surrounding the endothelial heart tube um it is very important to understand some terminologies so visceral drums cardiac muscles okay myoblast adhere to one another by special attachments that later develop into intercalated disc of the mature cardiomyocytes myofibrils develop as in skeletal muscles which means we exactly don't know how do they develop now during lateral later development a few special bundles of the muscle cells with irregularly disrupted myofibril becomes visible and these are proka G fibers and also the conducting system of the heart heart development how is the conducting system actually developed so but a generics muscles are developed from the visual misoderm surrounding the endothelial heart tube or is how the cardiovascular system is developed playlist videos smooth muscles for the doors aorta and large arteries is derived from the lateral plate mesoderm and the neural crest cells in the coronary arteries smooth muscle originate from the pro epicardial cells and neural crest cells a smooth muscles in the wall of the gut and the gut derivatives is derived from the visceral layer of the lateral plate mesoderm to is sphincter and the dilator muscles of the pupil are derived from the ectoderm it's a protein serum response factor it's a transcription Factor responsible for a smooth muscle differentiation smooth muscle banana that is by the release of srf by these cells now this factor is upregulated by growth factors through kinase phosphorylation Pathways myocardin and myocardium related transcription factors then act as co-activation this is too much of the detail for you to srf is required for differentiation of a cell into smooth muscle cell and what are the proteins yeah you know activating factors which are important for srf production they are myocardient and myocardial related transcription factors you know different parts of the mesoderm or different parts of the music they are significantly okay so the first Stables yeah so two tables are there this one origin of the muscles from the ebaxial and primaxial precursors cervical region of the embryo made primaxial mesodrome say yes structures they are all formed by this region Nothing by this region you know lead to development of these muscles and this is innervated by this nerve so that's kind of a ratification but this is worth remembering the table examples may say questions they have asked this okay now some clinical staff partial or complete absence of a muscle is common and it is common that some muscle is completely missing foreign a more serious defect is called Poland sequence that occur in one in 20 000 individuals and is characterized by absence of pectoralis minor and partial loss of pectoralis major so pectoral is minor and major loss is pollen sequence okay that's uh not very uncommon as well one in twenty thousand or is there are you know mispositioning of the nipple in areola and there are other uh congenital defect as well such as syndactylene short digits yeah so this is a diagram of the pollen sequence you see the pack major and minor are missing the nipple is shifted to an abnormal location so that sort of thing okay I don't know okay you cannot have a look at the syndic highly now another important thing is the pre-owned belly syndrome this is partial or complete absence of abdominal musculature usually the abdominal wall is so thin that the organs are visible and easily palpated an abdominal voltage or muscles this defect is sometimes associated with malformation of the urinary tract and bladder embryology General principle if there is one anomaly it is usually associated with other anomalies as well okay terminology muscular dystrophy discus muscular dystrophy it is a problem it's an x-linked recessive disease just made dystrophy Gene your head that is mutated and it's a very very severe disease which is known as Becker muscular dystrophy this is also mutation but that is a milder form of mutation compared to the duchenne muscular dystrophy however in the Duchene no functional dystrophin is made so duchenne is severe and Becker make functional distraction therefore the symptoms are more severe into chain Muscular Dystrophy and they are milder in Becker muscular dystrophy dystrophy is a cytoplasmic protein that form just of an Associated protein complex linking the cytoskeleton to the extracellular metrics so that's all about this chapter it's a very important chapter many students who they have chapter my coffee confused with their way but I hope this video is so I hope these concepts are very clear to you um if you like the video please share the video with your colleagues And subscribe the channel if you have not already done so absolutely