Flashcards in Muscle Structure And Adaptation Deck (47)
What do muscles form from in the embryo?
→ Somites (paraxial mesoderm)
What happens to mesodermal cells during development?
→ They go through a mesenchymal transition
→ The cells become columnar and form a transient cavity
→ They undergo an epithelial mesenchymal transition to form the sclerotome
What does the sclerotome consist of?
What is the myotome?
→ Muscle precursors
What is the dermomyotome?
→ Myotome and dorsal dermis
What is the syndetome?
What does the notochord do?
→ Induces the mesoderm to become myogenic by inducing myogenic regulatory factors
What do paracrine factors induce?
→ Myf5 and MyoD (myogenic transcription factors)
→ Notochord induces mesoderm to become myogenic
→ Paracrine factors induce Myf5 and MyoD which leads to myogenic commitment
→ myoblasts proliferate
→ Exit the cell cycle due to myogenin expression
→Structural proteins are expressed and myotubes form
→ Myotubes align and fuse parallel to each other
→ Biphasic muscle development : primary and secondary
→ Satellite cells : regeneration and post natal growth
What does myogenin expression mean?
What are the structural proteins expressed when myotubes form?
→ Actin and myosin
What can embryonic fibre number be affected by?
What happens to muscle mass after birth?
→ Increase in fibre size (hypertrophy)
What are satellite cells?
→ Muscle stem cells
What are muscle stem cells?
→ Undifferentiated muscle precursors that are self-renewing
When are MuSCs activated?
→ postnatal development
Why are muscle cells multinucleated?
→ They are big and long cells
→ huge production of structural proteins
→ this needs to occur along the length of the muscle fibre
What do myosin isoforms dictate?
→ Different chemomechanical transduction
→ ATP hydrolysis
→ Shortening velocity
What do troponin and tropomyosin isoforms dictate?
→ Determine sensitivity to Ca2+
What do titin isoforms dictate?
→ Elastic properties
What is an example of a type I fibre?
→ Back extensor muscle
What are type I fibres used for?
What are the properties of type I fibres?
→ High mitochondrial content - oxidative phosphorylation
→ Heavily vascularised
→ Sustained contraction
→ Abundant myoglobin
What are the properties of type II fibres?
→ High force contraction
→ Less mitochondria - glycolytic respiration
→ Poorly vascularised
What ratio of muscle fibres do untrained individuals have?
→ 50:50 fast to slow
What ratio of muscle fibres do long distance runners have?
→ 60-70% slow
What ratio of muscle fibres do sprinters have?
→ 80% fast
What are properties of powerlifters muscles?
→ Highly glycolytic
→ Fatigue easily
→ High muscle to total body mass ratio
→ muscle size interferes with locomotion
What is the order that MHC can split ATP in from fastest to slowest?
→ embryonic is the slowest