Muscle Structure And Adaptation Flashcards
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?
→ Bone
→ Ribs
→ Cartilage
What is the myotome?
→ Muscle precursors
What is the dermomyotome?
→ Myotome and dorsal dermis
What is the syndetome?
→ Tendons
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)
Describe myogenesis
→ 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?
→terminal differentiation
What are the structural proteins expressed when myotubes form?
→ Actin and myosin
What can embryonic fibre number be affected by?
→ temperature
→ hormones
→ Nutrition
→ Innervation
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?
→ training
→ 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?
→ Posture
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
→Fatigue easily
→ 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?
→ Hypertrophied → 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?
→ 2B → 2A → 2X → 1 → embryonic is the slowest
What is MHCexoc?
→ extraocular myosin heavy chain
What is MHCperi?
→ perinatal myosin heavy chain
What are the gene differences between males and females in terms of skeletal muscles?
→ >3000 genes
→ males have a larger fibre cross-sectional area
What is the difference between females and males in type I fibres?
→ males - 36%
→ females - 44%
What is the difference between females and males in type II fibres?
→ males - 41%
→ females - 34%
What is testosterone needed for?
→ development of the male reproductive system
What does testosterone develop?
→ Muscle + bone mass
→ body hair
→ deep voice
What kind of a steroid is testosterone?
→ Anabolic
What does testosterone do to muscle cells?
→ Commitment of mesenchymal pluripotent cells into myogenic lineage
What does testosterone inhibit?
→ inhibits adipogenesis
What does testosterone stimulate?
→ Satellite cell replication
→ muscle protein synthesis
→ fibre hypertrophy
What are the three adverse effects that synthetic anabolic steroids can have?
→ Increase BP
→ affect the heart
→ Shrinkage of testicles
What can be used for muscle mass loss?
→ testosterone
How does muscle recover from a minor injury such as a sprain?
→ Damaged muscle fibres necrose
→ There is an inflammatory response and neutrophils and macrophages respond to the damaged muscle fibre
→ There is an increase in satellite cell proliferation
→ they fuse with muscle fibres and regenerate them
How does muscle recover from laceration?
→ incomplete laceration
→ fibrotic tissue forms
What is sarcopenia?
→ age related loss of muscle mass
How much does muscle mass decrease after 30?
→ 3-8% decrease after 30
→ higher after 60
What is loss of muscle mass associated with?
→ gain in fat mass
→ decreased satellite cell number and recruitment
