Lect. 24 - Muscular Development Flashcards Preview

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Flashcards in Lect. 24 - Muscular Development Deck (22):

Myoblast stage

Derived from myogenic cells; postmitotic


Myotube stage

Formed when myoblasts line up and adhere to one another; requires Ca2++-dependent CAMs; involved in mRNA and protein synthesis; characterized by appearance of actin, myosin, troponin and tropomyosin; formation of sarcomeres; nuclei move to periphery


What is the role of satellite cells?

Located b/w sarcolemma and basal lamina; mitotic and myogenic; able to fuse w/ muscle fiber and provide for growth; note that satellite cells do not form new muscle fibers


Primary myotubes

Formed by fusion of earliest (embryonic) myoblasts; may already be distinguished as fast or slow in some species; differentiation occurs before innervation


Secondary myotubes

Smaller than primary; formed alongside primary from late (fetal) myoblasts; presence of motor axons may be necessary to form secondary myotubes; contained w/I same basal lamina and are electrically coupled


What is the role of FGF and TGF-beta in the differentiation of muscle tissue?

Maintain myogenic cells in the labile state


MyoD family

Able to convert non-muscle cells to cells capable of expressing muscle proteins; helix-loop-helix TF; forms dimer and binds to E box in enhancer region of myogenic genes; binding is enhanced when E12 replaces one member of the dimer to form a heterodimer; transcriptional inhibitor id can replace one member of the MyoD homodimer to form a heterodimer resulting in poor binding ability


Role of pax-3 and myf-5

Separately can activate MyoD and cause myogenic cells to become myoblasts; increasing Myf-5 along w/ MyoD results in expression of myoblast genes by myoblasts and expression of myogenin


Role of Myf-6

Myogenin results in expression of myotube genes myf-6; leads to expression of myofibers genes


Role of pax-7

Along w/ pax-3 induces MyoD w/ proliferation factors FGF and TGF-beta


Epaxial muscles of the trunk arise from ?

Dorsal lip of myotome


Epaxial tendons of the trunk arise from ?

Syndetome layer w/I somites


Hypaxial muscles of the trunk arise from?

Ventral buds of myotome


Tendons of Hypaxial muscles of the trunk arise from?

Lateral plate mesoderm


Limb muscles arise from?

Ventrolateral dermomyotome


Tendons of limb muscles arise from?

Lateral plate mesoderm


Muscles of the head and the neck are mostly derived from?

Par axial somitomeres


Extraocular muscles arise from?

Pre chordal plate


Most of the cranial musculature is derived from?

Unsegmented paraxial mesoderm


Some cranial musculature (lower jaw) is derived from ?

Splanchnic mesoderm


Cardiac muscle is derived from?

Splanchnic mesoderm


Myogenic cell stage

Originate in somites; resemble mesenchymal cells; restricted to muscle-forming line; mitotic cells