Skeletal muscle development and growth Flashcards
What are the primary germ layers?
- zygote
- blastula
- gastrula
From the gastrula, what are the layers?
- ectoderm (outer)
- mesoderm (middle)
- endoderm (internal)
- germ cells
What is the paraxial mesoderm?
- organised into somites
- somites give rise to axial skeleton and muscles, limb muscles and dermis
What is the intermediate mesoderm?
gives rise to urogenital system
What is the lateral mesoderm?
- heart (endo, epi, pericardium)
- blood
- endothelium (lining of blood vessels)
- wall of gut
- wall of respiratory tract
- lining of body cavites
Generally, what do you generate from the mesoderm?
muscle tissue
Explain the general process of somitogenesis:
- The paraxial mesoderm develops into the somitic mesoderm
- Somitic mesoderm has the layers of columnar cells, somitocoel and mesenchymal cells
- This develops into the somite with both sclerotome and dermomyotome
- Dermomyotome separates into dermatome and myotome
- The purpose of these is to make stem cells more committed to their tissue types
What does the myotome develop into?
epaxial and hypaxial muscles
+
flexor and extensor muscles
what is the paraxial mesoderm also known as?
rostrocaudal strip
What is the sclerotome subdivided into?
rostral and caudal halves
The rostral and caudal halves are separated laterally by?
von Ebner’s fissure
These half somites of the sclerotome contribute to?
- single vertebral level body
- intervertebral disc
What is the dermatome?
- connective tissue underlying the epidermis
- begins as dorsal thickening
- spreads throughout body
What are the 2 parts of the myotome and what does it develop into?
body = epaxial and hypaxial muscles
limbs = flexor and extensor muscles
What do the epaxial muscles consist of?
vertebrae, ribs, base of skull
what do the hypaxial muscles consist of?
vertebral, diaphragm, abdominals and limbs
Explain the step by step cellular and molecular mechanisms in the development from the dermamyotome:
- Delamination - cells peel away from tissue and involves Pax3 activating c-met
- Migration - cells become more specific and factors like HGF switched on to contribute to the migration
- Proliferation - asymmetric division so cells don’t run out
- Determination - to particular lineage, with key factor MyoD which upregulates proteins for development of muscles
- Differentiation - Myogenin involved along with other factors to eventually form specific muscles
Explain skeletal muscle development from a progenitor to a motor unit:
- mesodermal progenitor
- mono-nucleated myoblast
- multi-nucleated myotube
- innervated mature myofibre
- functional motor unit
Basically, going from division, alignment, fusion then innervation
Name the 3 steps in embryonic myogenesis:
- Determination
- Differentiation
- Maturation
Name the myogenic factors:
- Pax3
- MyoD
- MYF-5
- MRF-4
- Myogenin
Name the negative regulator of myogenesis:
myostatin
Break down the extracellular matrix:
- fibronectin
- decorin
- embryonic collagens
- proteoglycans
- specific collagens, endomysium, perimysium, epimysium
Explain the process from somites to a mature muscle:
- Somite - in FN-rich matrix
- Somite differentiation - maturation of basement membrane
- Myofibre differentiation - maturation of interstitial matrix
- Mature muscle - establishment of COL-rich matrix
What type of division is stem cell expansion?
symmetric stem cell division
What type of division is stem cell maintenance?
asymmetric stem cell division
What type of proliferation is stem cell commitment?
progenitor proliferation
What role does tryptophan and serotonin play?
regulate growth, happy hormone
What is the central regulator of things like tryptophan and serotonin?
GHRH
How does postnatal muscle development, regeneration and adaptation occur?
- satellite cell activation due to muscle injury or exercise
- this either goes into self-renewal or cell proliferation and chemotaxis
- from there, the satellite cells could fuse to produce new muscle fibres
- OR the satellite cells fuse to injured muscle fibres but eventually regenerative muscle fibres with the central nuclei will become intact
- then the satellite cell becomes quiescent
What’s the purpose of postnatal muscle development, regeneration and adaptation?
mechanism in place to ensure development, growth and adaptation in perinatal and postnatal periods
