Muscle Structure And Adaptation Flashcards
What do muscles form from in the embryo?
β Somites (paraxial mesoderm)
What happens to mesodermal cells during development?
β They go through a mesenchymal transition
β The cells become columnar and form a transient cavity
β They undergo an epithelial mesenchymal transition to form the sclerotome
What does the sclerotome consist of?
β Bone
β Ribs
β Cartilage
What is the myotome?
β Muscle precursors
What is the dermomyotome?
β Myotome and dorsal dermis
What is the syndetome?
β Tendons
What does the notochord do?
β Induces the mesoderm to become myogenic by inducing myogenic regulatory factors
What do paracrine factors induce?
β Myf5 and MyoD (myogenic transcription factors)
Describe myogenesis
β Notochord induces mesoderm to become myogenic
β Paracrine factors induce Myf5 and MyoD which leads to myogenic commitment
β myoblasts proliferate
β Exit the cell cycle due to myogenin expression
βStructural proteins are expressed and myotubes form
β Myotubes align and fuse parallel to each other
β Biphasic muscle development : primary and secondary
β Satellite cells : regeneration and post natal growth
What does myogenin expression mean?
βterminal differentiation
What are the structural proteins expressed when myotubes form?
β Actin and myosin
What can embryonic fibre number be affected by?
β temperature
β hormones
β Nutrition
β Innervation
What happens to muscle mass after birth?
β Increase in fibre size (hypertrophy)
What are satellite cells?
β Muscle stem cells
What are muscle stem cells?
β Undifferentiated muscle precursors that are self-renewing
When are MuSCs activated?
β training
β postnatal development
Why are muscle cells multinucleated?
β They are big and long cells
β huge production of structural proteins
β this needs to occur along the length of the muscle fibre
What do myosin isoforms dictate?
β Different chemomechanical transduction
β ATP hydrolysis
β Shortening velocity
What do troponin and tropomyosin isoforms dictate?
β Determine sensitivity to Ca2+
What do titin isoforms dictate?
β Elastic properties
What is an example of a type I fibre?
β Back extensor muscle
What are type I fibres used for?
β Posture
What are the properties of type I fibres?
β High mitochondrial content - oxidative phosphorylation
β Heavily vascularised
β Sustained contraction
β Abundant myoglobin
What are the properties of type II fibres?
β High force contraction
βFatigue easily
β Less mitochondria - glycolytic respiration
β Poorly vascularised
What ratio of muscle fibres do untrained individuals have?
β 50:50 fast to slow
What ratio of muscle fibres do long distance runners have?
β 60-70% slow
What ratio of muscle fibres do sprinters have?
β 80% fast
What are properties of powerlifters muscles?
β Hypertrophied β Highly glycolytic β Fatigue easily β High muscle to total body mass ratio β muscle size interferes with locomotion
What is the order that MHC can split ATP in from fastest to slowest?
β 2B β 2A β 2X β 1 β embryonic is the slowest
What is MHCexoc?
β extraocular myosin heavy chain
What is MHCperi?
β perinatal myosin heavy chain
What are the gene differences between males and females in terms of skeletal muscles?
β >3000 genes
β males have a larger fibre cross-sectional area
What is the difference between females and males in type I fibres?
β males - 36%
β females - 44%
What is the difference between females and males in type II fibres?
β males - 41%
β females - 34%
What is testosterone needed for?
β development of the male reproductive system
What does testosterone develop?
β Muscle + bone mass
β body hair
β deep voice
What kind of a steroid is testosterone?
β Anabolic
What does testosterone do to muscle cells?
β Commitment of mesenchymal pluripotent cells into myogenic lineage
What does testosterone inhibit?
β inhibits adipogenesis
What does testosterone stimulate?
β Satellite cell replication
β muscle protein synthesis
β fibre hypertrophy
What are the three adverse effects that synthetic anabolic steroids can have?
β Increase BP
β affect the heart
β Shrinkage of testicles
What can be used for muscle mass loss?
β testosterone
How does muscle recover from a minor injury such as a sprain?
β Damaged muscle fibres necrose
β There is an inflammatory response and neutrophils and macrophages respond to the damaged muscle fibre
β There is an increase in satellite cell proliferation
β they fuse with muscle fibres and regenerate them
How does muscle recover from laceration?
β incomplete laceration
β fibrotic tissue forms
What is sarcopenia?
β age related loss of muscle mass
How much does muscle mass decrease after 30?
β 3-8% decrease after 30
β higher after 60
What is loss of muscle mass associated with?
β gain in fat mass
β decreased satellite cell number and recruitment
