Embryonic Development of the Muscular System PDF

(002) EMBRYONIC DEVELOPMENT OF THE MUSCULAR SYSTEM DR. GAIL TANAWIT | 12/07/20 OUTLINE have the intermediate mesoderm and the lateral plate...

(002) EMBRYONIC DEVELOPMENT OF THE MUSCULAR SYSTEM DR. GAIL TANAWIT | 12/07/20 OUTLINE have the intermediate mesoderm and the lateral plate mesoderm. I. MUSCULAR SYSTEM OVERVIEW It is the paraxial because it’s just beside the axis. A. Skeletal - Paraxial Mesoderm The center axis would be your neural tube. B. Smooth – visceral (splanchnic) mesoderm Lateral to the paraxial mesoderm would be the intermediate C. Cardiac muscle – visceral (splanchnic) mesoderm. mesoderm II. STRIATED SKELETAL MUSCLE A. Axial SKELETAL- PARAXIAL MESODERM B. Ventral The most lateral would be the lateral plate mesoderm. 1. Sclerotome As you can see in the figure, your paraxial mesoderm C. Upper region of Somite would be comprise depending on the area. 2. Dermatome If you are in the cephalic area then it is composed of somites from the occipital area. 3. Ventrolateral lips If you are on the inferior, you have somites forming the 4. Dorsomedial lips sacral region. D. Lateral Somitic Frontier In the most superior cephalic part, the head, we call it the 1. Primaxial Domain somitomeres. 2. Abaxial Domain Forms the back of the embryo, along the spine. III. SKELETAL MUSCLES AND TENDONS The paraxial, depending on the area (more on caudally), A. Myoblasts will comprise also the back muscles along the spines. IV. MOLECULAR REGULATION OF THE MUSCLE SOMITES – a series of dorsal paired segments (right and DEVELOPMENT left) occurring along the notochord in the embryo. V. PATTERNING OF MUSCLES Paraxial can be further subdivided into two: A. Head Musculature - Head or somitomeres B. Limb Musculature - Somite VI. CARDIAC MUSCLE Somite will give rise to: VII. SMOOTH MUSCLE - Sclerotome VIII. CLINICAL CORRELATES o It will form the cartilage and bony framework A. Polland Sequence for the vertebra B. Abnormalities of Hair Distribution - Syndotome C. Muscular Dystrophy: Duchene MD o Will give rise to tendons D. Muscular Dystrophy: Becker MD - Myotome o skeletal muscle proper - Endothelial cells I. MUSCULAR SYSTEM OVERVIEW - Dermatome o dermis and skeletal muscle Muscular system develops from the mesodermal germ Intermediate mesoderm will give rise to: layer except some smooth muscles. - Kidneys and gonads Remember that in the embryology, you have the ectoderm, Smooth muscle in particular will be coming from Lateral the mesoderm and the endoderm as the germ layers. Plate Mesoderm. But for the muscle usually it would be coming from the mesodermal germ layer. SMOOTH- VISCERAL (SPLANCHNIC) MESODERM Surrounding the gut and its derivatives and from ectoderm Exception: There are also smooth muscles that are derived from ectoderm. They are not coming from mesoderm but from ectoderm. - pupillary muscle - mammary gland muscles - sweat gland muscles CARDIAC- VISCERAL (SPLANCHNIC) MESODERM Also from visceral or splanchnic mesoderm, from lateral Figure 1. Summary of mesoderm development. plate mesoderm We have the neural tube as the point of reference, Give rise to heart muscle immediately beside the neural tube would be your paraxial Surrounding the heart tube. mesoderm, the left and right paraxial mesoderm. And we Visceral Mesoderm Page 1 of 6 PREPARED BY: CMED 1D  (002) EMBRYONIC DEVELOPMENT OF THE MUSCULAR SYSTEM DR. GAIL TANAWIT | 12/07/20 - All internal organs except the ectoderm derived - muscle proper smooth muscle (pupillary, mammary gland and sweat gland muscles). - Mammary gland o Its myoepithelial cell for milk ejection reflex cannot be controlled because it’s a smooth muscle. II. STRIATED SKELETAL MUSCLE Derived from 7 somitomeres if it’s from the cranial region Partially segmented from the paraxial mesoderm if more caudally Somites (form occipital to tail bud) AXIAL SKELETAL MUSCLE body wall and limbs muscles undergo epithelialization - form a ball of epithelial cells with central cavity (a basketball with a hollow center containing the air VENTRAL REGION the ventral region of each somite then becomes mesenchymal again and forms the sclerotome. become sclerotome (bone forming for ribs and vertebrae) UPPER REGION OF SOMITE Figure 3. Cross sectional drawings showing the stages of Upper region of somites become: development in somite. - Dermatome This is the notochord on the anterior, you have the neural - Ventrolateral lips tube (it will closed), then it will be covered by ectoderm. o Paraxial Mesoderm- skeletal muscle What happens is that you have epithelialization, wherein o Tongue muscle, Infrahyoid, abdominal wall there’s a cavity at the center. muscles (rectus abdominis, oblique muscle There’s a ventral somite wall and dorsal. and transversus), limb muscles Cells in the ventral and medial walls of the somite lose their o Infrahyoid, abdominal wall (rectus and epithelial characteristics and migrate around the neural transversus), limb muscles tube and notochord (as you can see on the second Dorsomedial lips picture), and some move into the parietal layer plate o Paraxial Mesoderm- skeletal muscle mesoderm. o Back, shoulder and intercostal Collectively, these cells constitute the sclerotome that would give rise to cartilage. Cells at the DML and VLL regions of the somite form muscle cell precursors. Cells from both regions migrate ventral to the dermatome to form the dermomyotome. In combination, somitic cells and lateral plate mesoderm cells will form now another groove called the abaxial mesodermal domain. Those that go to the lateral side will become abaxial. (Ab = Abduction, to the lateral side) Primaxial mesodermal domain Figure 2. Remaining cells of deromyotome becomes mesenchymal - Remain at the center cells called dermatome to form dermis. - Contains somitic cells Together, dermatome cells and the muscle cells that SCLEROTOME associate with them will now form the dermomyotome. - cartilage of vertebra and part of ribs DERMAMYOTOME - remaining portion if the somite contains precursor for LATERAL SOMITIC FRONTIER dermis and skeletal muscle. Green portion on the picture DERMATOMES Imaginary border - dermis ( mesenchymal connective tissue of the skin) Separates two mesoderamal domains MYOTOME Page 2 of 6 PREPARED BY: CMED 1D  (002) EMBRYONIC DEVELOPMENT OF THE MUSCULAR SYSTEM DR. GAIL TANAWIT | 12/07/20 1. Primaxal Domain SCLERAXIS -transcription factors that regulates development Around neural tube containing paraxial mesoderm of tendons. (somite derived cells) Signals from neural tube and notochord IV. MOLECULAR REGULATION OF THE MUSCLE 2. Abaxial Domain DEVELOPMENT Parietal layer of lateral plate mesoderm Bone morphogenetic protein 4 (BMP4) and probably fibroblast growth factors from LPM (Lateral Plate Somite crossed the frontier and enter lateral plate Mesoderm), together with WNT proteins, signal VLL cells of layer. the dermomyotome to express the muscle-specific gene signals from lateral plate mesoderm MyoD. Defines dermis border from LPM and dermis from BMP4 secreted by ectoderm cells induces production of the back. WNT proteins by dorsal neural tube at the same time that Both receives signals from spinal nerve low concentrations of Sonic Hedgehog (SHH) proteins innervation. reach the DML cells of the dermomyotome. WNT + SHH (notochord and floor plate of neural tube) induce expression of MYF5 and MyoD in dorsomedial (DML) cells. MYF5 and MyoD are members of a family of transcription factors called Myogenic regulatory factors (MRF). This group of genes activate pathways for muscle development. Figure 4. Transverse section through the trunk of a chickembryo on days 2-4. Somites visible as the red structures are multipotent at this point and their specification is dependent upon their location relative to paracrine factors received from surrounding tissues(such as the Figure 5. Expression patterns of genes that regulate somite neural tube, epidermis, etc.) differentiation. III. SKELETAL MUSCLES AND TENDONS LIMB MUSCULATURE MYOBLASTS pre-cursor cells Fuse and form long, multinucleated muscle fibers Myofibrils soon appear in the cytoplasm by the end of third month, cross-striations, typical of skeletal muscle appear A similar process occurs in the seven somitomeres in the head region rostral to the occipital somites. However, somitomeres never segregate into recognizable regions of sclerotome and dermomyotome segments prior to differentiation. Figure 6. Determination of Somites TENDONS -for the attachment of muscles to bones are derived from sclerotome cells lying adjacent to myotomes at Myotome will be divided into 2 (Abaxial and Primaxial the anterior and posterior borders of somites domain) Page 3 of 6 PREPARED BY: CMED 1D  (002) EMBRYONIC DEVELOPMENT OF THE MUSCULAR SYSTEM DR. GAIL TANAWIT | 12/07/20 Abaxial: follow order from Wnt1, Wnt3a (neural tube) - Originates from the proepicardial cells and neural crest Primaxial: Shh (from notochord and floor plate of neural cells. tube), WNT (ectoderm), and BMP4 (Lateral Plate 3. Gut and gut derivatives Mesoderm) - Derived from the visceral layer of the lateral plate Notochord: degenerates through apoptosis (remnants mesoderm (LPM). remain as nucleus pulposus) 4. Pupil, Mammary and Sweat Glands - Derived from the ectoderm. - V. PATTERNING OF MUSCLES Patterns of muscle formation are controlled by connective tissue into which myoblasts migrate. SERUM RESPOSE FACTOR (SRF) Neural Crest Cells is a transcription factor responsible for smooth muscle cell - where connective tissues in the head region are differentiation. derived Upregulated by Growth Factors through kinase Somitic mesoderm phosphorylation pathways. - where connective tissues from cervical and Co activators are Myocardin and Myocardin- related occipital regions are differentiated Transcription FactorS (MRTFs) to enhance the activity of Parietal layer of Lateral Plate Mesoderm SRF, thereby initiating the genetic cascade responsible for - where connective tissues in the body wall and smooth muscle development. limbs originated VIII. CLINICAL CORRELATES HEAD MUSCULATURE 1. Poland Sequence Occurs in 1 per 20,000 individuals All voluntary muscles of the head are derived from Characterized by absence of pectoralis minor Paraxial mesoderm, including musculature of: and partial loss of pectoralis major (usually the - Tongue sternal head) muscles - Eye except iris (from optic cup mesoderm) Nipple Areola Complex can also be absent or - Pharyngeal arch muscle Displaced the patterns of muscle formation in the head are It could be a problematic deformity especially if it directed by connective tissue elements derived from is a female because the breast would be neural crest cells necessary for nourishment of the baby later on is observed in the 7TH week of development - Digits (fingers) can be defective (fusing or As in other regions, connective tissue dictates the webbing) pattern of muscle formation, and this tissue is derived Example: fingers of a duck or syndactyly (fusing from parietal layer of lateral plate mesoderm which or webbing) or brachydactyly (shortening) of also gives rise to bones and muscle limbs fingers Mesenchyme is derived from dorsolateral cells of the somites that migrate into the limb bud to form the muscles. VI. CARDIAC MUSCLE develops from the splanchnic/visceral mesoderm surrounding the heart tube. Myoblasts adhere to one another by its special attachments called Intercalated Discs Unlike the skeletal muscles, myoblasts do not fuse. During later development, a few special bundles of muscle cells would have irregular myofibril that gives rise to purkinje fibers. Purkinje muscle fibers- form the conducting system of the Figure 11.5 Poland sequence. The pectoralis minor and heart part of the pectoralis major muscles are missing on the patient’s left side. Note dis- placement of the nipple and VII. SMOOTH MUSCLE areola. 1. Large arteries and dorsal aorta 2. Prune Belly Syndrome - Is derived from the lateral plate mesoderm and neural Partial or complete absence of abdominal crest. musculature 2. Coronary arteries Abdominal muscles are thin and wrinkled. Page 4 of 6 PREPARED BY: CMED 1D  (002) EMBRYONIC DEVELOPMENT OF THE MUSCULAR SYSTEM DR. GAIL TANAWIT | 12/07/20 Organs are palpable and are visible Urinary bladder defect could also be found These defects cause an accumulation of fluid that distends the abdomen, resulting in atrophy of the abdominal muscles. Figure 11.6 Prune belly syndrome: a distended abdomen from atrophy of abdominal wall musculature. Figure 9. Duchenne Muscular Dystrophy 3. Muscular Dystrophy TEST YOUR KNOWLEDGE is the term for a group of inherited tnuscle diseases that cause Progressive muscular MULTIPLE CHOICES wasting and weakness. 1. Which area of the mesoderm are skeletal muscles derived from? A. Paraxial mesoderm A. Duchene Muscular Dystrophy (DMD) B. Primaxial domain Most common C. Visceral(sphlanchnic) mesoderm Occurs 1:4,000 male births D. None of the above Inherited as X-linked recessive For male, you need 2 small X (xx) for it to 2. Smooth muscle tissues that arise from the ectoderm. manifest A. Pupillary For female, 1 small X (x) would be balance by B. Mammary gland dominant big X (X), so no manifestation. So, C. Sweat gland females can be a carrier. D. All of the above If male marries a female carrier so that would be 3. What are the sign of duchenne muscular dystrophy? more problematic A. Tiptoeing NO dystrophin present B. Lordosis Is severe and earlier manifested at