Embryology of the Muscular System PDF

Embryology of the Muscular System  Introduction Formation of the muscular system begins about the 4th week of embryonic development. Precursor cells are called myoblast. Majority of the muscular system develops from the mesoderm. Exceptions are muscles of the ir...

Embryology of the Muscular System  Introduction Formation of the muscular system begins about the 4th week of embryonic development. Precursor cells are called myoblast. Majority of the muscular system develops from the mesoderm. Exceptions are muscles of the iris, myoepithelial cells of mammary and sweat glands which develop from the ectoderm.  Introduction The muscular system consist of: I. Skeletal muscles. II. Cardiac muscles. III. Smooth muscles. Skeletal muscles are derived from paraxial mesoderm. This forms ; I. Somites form the occipital to the sacral regions Intraembryonic Mesoderm  Introduction Smooth muscles differentiate from the splanchnic mesoderm surrounding the gut and its derivatives Cardiac muscles are derived from splanchnic mesoderm surrounding the heart tube.  Skeletal Muscles Musculatures of the head, axial skeleton and body wall are formed by somites and somitomeres. From the occipital region caudally, somites form and differentiate into; I. Sclerotome II. Dermatome III. Two muscle forming regions One in the dorsolateral region of the somite, provides progenitor cells for limb and body wall muscles (hypomeric) The other in the dorsomedial region forms the myotome (epimeric)  Skeletal muscles Precursor cells (myoblast), fuse and form long, multinucleated muscle fibers. Myofibrils soon appear in the cytoplasm, cross striations appear in at the end of the third month. Similar mechanism occur in the 7 somitomeres in the head region rostral to the occipital somites,