Anatomy and embryology of skeletal muscle Flashcards
Function of skeletal muscle
Force generation for breathing and movement
Force generation for postural support (helping you stand up)
Heat generation (shivering)
Metabolism (AA reservoir)
Describe the types of muscle
Skeletal - striated, multinucleate, unbranched; somatic nervous system
Cardiac - striated, branched, has intercalated discs; autonomic nervous system
Smooth - spindle shaped cells, non-striated; autonomic nervous system
Syncytial meaning
Giant multinucleate cell
Describe tendons
Made of type I collagen; connects bone to muscle - transfers muscle force to bone
What are the two main types of muscle contraction?
Isotonic (muscle length changes with force production)
Isometric (muscle length doesn’t change with force production)
What are the types of isotonic muscle contraction?
Concentric = muscles shorted during contraction Eccentric = muscle produces a force but length increases (bicep when controlling lowering of a weight)
Prime mover
Agonist - concentric contraction
Antagonist
Opposes the action of prime mover
Fixator
Steadies position through isometric contraction (lumbar muscles)
Synergist
Complements action of prime mover
Describe the structure of a muscle bundle
Epimysium = outermost layer (tough) that surrounds entire muscle Perimysium = surrounds bundles of muscle fibres, creates a fascicle Endomysium = surrounds muscle fibres
Formation of skeletal muscle
Myoblasts undergo proliferation when encouraged by growth factors; then when growth factors are removed they fuse into a myotube (muscle fibre)
Describe satellite cells
Stem cells which are mitotically quiescent, can be encouraged to enter the cell cycle to form myoblasts; self renewing so can replace themselves.
What are satellite cells important for?
Muscle growth after birth;
Muscle maintenance;
Muscle hypertrophy + repair, regeneration
What can effect the speed of contraction of a muscle
The myosin heavy isoform present in the sarcomere
What are the subdivisions of muscle by speed?
Type I (slow, oxidative) Type IIa (fast, oxidative) Type IIb (fast, glycolytic) Type IIx (super-fast, glycolytic)
Where is fast/slow myosin found?
Fast in white muscle (not much myoglobin)
Slow in red muscle (plenty of myoglobin)
Describe muscle innervation
Each myofibre receives innervation from one motor neuron at a neuromuscular junction.
What causes Duchenne muscular dystrophy, why is it degenerative?
Disruption of dystrophin - helps link contractile units to ECM so stabilises like a shock absorber.
Contractile tissue replaced by fibrous tissue progressively.
What are somites?
Embryonic structures that give rise to muscles; types are dermomyotome, sclerotome and myotome
What does a dermomyotome give rise to?
Skeletal muscle, dermis and satellite cells
What does a sclerotome give rise to?
Cartilage, bone, tendons, endothelial cells
What does a myotome give rise to?
Differentiated myocytes
Describe embryonic muscle fibre formation
Myogenic precursors are encouraged to proliferate and form myoblasts by myogenic regulatory factors (Myf5 + Mrf4); which are then encouraged to differentiate + fuse into myotubes (Mrf4, myogenin)
What are MRFs
Myogenic regulatory factors
What MRFs are responsible for proliferation of myogenic precursors?
Myf5, Mrf4
What MRfs are responsible for differentiation/fusion of myoblasts?
Mrf4, myogenin
Myofibre
A skeletal muscle fibre
Myonucleus
A nucleus in syncytial muscle fibre
`Myofibril
Rod-like structure of many sarcomeric units in series
Myogenesis
Process of making skeletal muscle
Myoblast
Proliferative cell, makes skeletal muscle
Myocyte
Mononucleated differentiated muscle cell
Myotube
Immature muscle fibre
