Development of the musculoskeletal system Flashcards
What embryonic germ layer is skeletal muscle derived from?
Paraxial mesoderm
Where are the epaxial muscles located and what do they form upon maturation?
They are dorsal to the transverse processes and form the intrinsic muscles of the back
What line do myotomes originate from?
Somites
Formed by the cells at the ventrolateral lip (VLL) of the prospective myotome region and by cells from the dorsomedial lip (DML)
What portion of the mesoderm do VLL contribute cells to?
Cells at the ventrolateral lip contributes cells to both the primaxial and abaxial domains of the mesoderm
What portion of the mesoderm do DML contribute cells to?
Cells at the dorsomedial lip contribute to the primaxial domain of the mesoderm (also includes sclerotome and dermatome cells)
What cells does the primaxial domain contain? What does this domain form?
Cells from the paraxial mesoderm.
Forms muscles of the back, shoulder girdle (rhomboids, levator scapulae, and latissimus dorsi), and intercostals
What cells form dermis on the back (from dermatomes), vertebrae, and bony parts of the ribs (from sclerotome)?
Paraxial cells
What does the abaxial domain form?
Limb and abdominal wall (obliques and transversus abdominus muscles)
What do abaxial cells form?
The dermis in the body wall (from lateral plate mesoderm) and rib cartilages (from sclerotome cells that migrate across the lateral somitic frontier)
Where do migrating muscle cells receive innervation from?
Their spinal segments of origin - migrating muscle cells carry these spinal nerves with them as they migrate
What molecular regulation is important for the formation of skeletal muscle?
WNT, MyoD, BMP4 with low SHH
Describe the patterning of the muscles in the head
Head musculature formed by somitomeres - tongue, eye (except those of the iris = pupillary muscles = derived from the optic cup) and pharyngeal arches.
Muscles in the head are patterned by connective tissue that is formed by neural crest
Describe the patterning of the muscles of the limb:
Limb muscles formed by VLL cells: patterned by connective tissue formed by lateral plate mesoderm regulated by MyoD genes (transcription factor)
Describe the formation of cardiac muscle:
Derived from visceral mesoderm surrounding heart tube
Intercalated discs
Purkinje fibers
Describe the formation of smooth muscle:
Embryonic derivative of visceral layer of lateral plate mesoderm, some neural crest cells for sphincter and dilater
Molecular commitment — SRF, MRTFs
Paraxial mesoderm forms ________ along the spinal cord and somitomeres in the head.
Somites
What are the three components of somites?
Dermatome (skin)
Myotome (muscle)
Sclerotome (bone)
What is mesenchyme tissue?
Mesenchyme tissue = any loose connective tissue regardless of origin (i.e. neural crest cells)