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Flashcards in Muscular Development Deck (15):

What are myoblasts?

-derived from myogenic cells



What are myotubes?

-formed when myoblasts line up and adhere to one another

-requires calcium dependent CAMs

-involved in mRNA and protein synthesis

-characterized by appearance of actin, myosin, troponin, and tropomyosin

-formation of sarcomeres

-nuclei move to periphery


All skeletal muscle originates in what?

Somites or somitomeres


What are satellite cells?

-located between sarcolemma and basal lamina

-mitotic and myogenic

-able to fuse with muscle fiber and provide for growth

-satellite cells do not form new muscle fibers


Differentiate between primary myotubes and secondary myotubes.

-formed by fusion of earliest embryonic myoblasts

-may already be distinguished as fast or slow in some species

-differentiation occurs before innervation

-smaller than primary

-formed alongside primary from fetal myoblasts

-presence of motor axons may be necessary to form secondary myotubes

-contained within same basal lamina and are electrically coupled


What two things maintain myogenic cells in labile state?

-FGF and TGF-beta


What causes a loss of mitotic capability?



What are the stages of differentiation in myogenic cells?

-originate in somites

-resemble mesenchymal cells

-restricted to muscle forming line

-mitotic cells


What does the MyoD family do?

-able to convert non-muscle cells to cells capable of expressing muscle proteins

-helix loop helix transcription factors

-forms dimer and binds to E box in enhancer region of the 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 homodimers to form a heterodimer, resulting in poor binding ability


What regulates MyoD?

Pax-3 and Myf-5 separately can activate MyoD and cause myogenic cells to become myoblasts


What can increasing levels of MyoD result in?

-along with Myf-5, can result in expression of myoblast genes by myoblasts and expression of myogenin

-myogenin results in expression of myotubes genes and Myf-6

-Myf-6 leads to expression of myofiber genes


What are the origins of the muscles of the trunk?

-epaxial muscles arise from dorsal lip myotome

-epaxial tendons arise from syndetome layer within somites

-hypaxial muscles arise from ventral buds of myotome

-tendons arise from lateral plate mesoderm


What derives the muscles of the limbs?

-limb muscles arise from ventrolateral dermomyotome

-tendons from lateral plate mesoderm


Where are muscles of the head and neck derived from?

-mostly from paraxial somitomeres

-extra ocular muscles from prechordal plate

-most of the cranial musculature from unsegmented paraxial mesoderm

-cranial musculature (lower jaw) from splanchnic mesoderm


Where is cardiac muscle derived from?

-splanchnic mesoderm

-early cardiac muscle does not express MyoD

-both cardiac muscle cells and skeletal muscle cells express MADS

-cardiac muscle cells contract early

-early cardiac muscle cells maintain their ability to divide by partially disassembling their contractile apparatus prior to cell division

-cardiac muscle cells remain as mononucleated cells and attach to each other via intercalated discs