3 - Skeletal Muscles Flashcards
What is the dermomyotome
The remaining epithelial part of the somite after sclerotome cells migrate, which gives rise to muscle and dermis
What do epaxial myoblasts form
Deep back muscles and other segmented axial muscles
What do hypaxial myoblasts form
Muscles of the body wall, intercostal muscles, limbs, and tongue
Where do hypaxial myoblasts migrate to differentiate
Into the body wall, within the lateral plate mesoderm (LPM)
Name 3 key signalling molecules involved in dermomyotome differentiation
Sonic Hedgehog (Shh), Wnt proteins, BMP4
What does Noggin do during dermomyotome development
Inhibits BMP signalling to allow proper medial patterning
Where do myogenic progenitor cells originate
At the dorsomedial and ventrolateral lips of the dermomyotome
What do these progenitor cells form when they migrate
The primitive myotome
Which signals influence the specification of myogenic progenitors
Wnt
BMP signalling
What happens first during myogenesis
Myoblasts proliferate in the presence of FGFs but do not differentiate
How is differentiation initiated
When FGFs are depleted, myoblasts secrete fibronectin and express α5β1 integrin
What occurs during alignment
Myoblasts align into chains using cell adhesion molecules like cadherins
What is required for myoblast fusion
Calcium signalling, meltrins (metalloproteases), and myogenin
What role does IL-4 play in myogenesis
It recruits more myoblasts to the myotube, aiding maturation
What happens in the final stage of myotube formation
Myotubes mature into muscle fibres, connect to tendons, and begin contraction
What is MyoD
A master transcription factor in the bHLH family that determines muscle cell fate
What activates MyoD expression
Paracrine signals such as Wnt and BMP
Which other factors work with MyoD in myogenesis
Myf5
Myogenin
MRF4
Where do head muscle cells originate
From anterior paraxial mesoderm
Where do limb, diaphragm, and tongue muscle cells originate
From the hypaxial dermomyotome (ventrolateral lip)
Where do back muscle cells originate
From the epaxial dermomyotome (dorsomedial lip)
What tissues contribute connective tissue for muscle organisation
Somites and lateral plate mesoderm (LPM)
What is primary myogenesis
Formation of primary myotubes from early myoblasts; slow-twitch fibres, aligned with the anterior-posterior axis
What is secondary myogenesis
Formation of secondary myotubes around primary ones; fast-twitch fibres, make up adult muscle
What occurs during foetal myogenesis
Growth and maturation of muscle masses and onset of innervation
Describe skeletal muscle fibres
Large, multinucleated, cylindrical cells enclosed by a basement membrane
What are the 3 connective tissue layers in muscle
Endomysium (around fibres)
Perimysium (around fascicles)
Epimysium (around whole muscle)
What roles do connective tissues play in muscle organisation
Support structure, route for nerves and blood vessels, integration with tendons
What are satellite cells
Adult muscle stem cells located beneath the basement membrane, essential for muscle growth and repair
