Muscle fibres Flashcards
Properties of skeletal muscle fibres
Each muscle cell known as fibre
Striated
Syncytium (multinucleated)
Cells large
Arranged in bundles known as fascicles
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What is the sliding filament theory
Muscle shortening occurs due to movement of actin filament over myosin filament
Formation of cross bridges between actin & myosin filaments
Reduction in distance between Z lines of sarcomere
Explain cross bridge formation
Tropomyosin located along both chains of actin filaments & when calcium is low blocks binding of myosin to actin (fibre at rest)
Troponin complex is attached to each tropomyosin
What is the role of calcium in muscle contraction
Troponin captures Ca2+ & undergoes conformational change that lifts tropomyosin away from actin filament
What are the skeletal muscle fibre types
Fast fibres:
Type IIa (slowest of fast)
Fast oxidative
Type IIb (fastest of fast)
Fast glycolytic
Type IIx
Intermediate properties
Slow fibres:
Type I
Slow oxidative
Properties of fibre types
What are the main forelimb extensors and flexors
Extensors:
Triceps brachii extends elbow joint
Flexor carpi radialis & flexor carpi ulnaris extend wrist joint
Flexors:
Biceps brachii flexes elbow joint
Flexor carpi radialis & flexor carpi ulnaris flex wrist joint
What are the main hindlimb extensors and flexors
Extensors:
Quadriceps femoris extends knee joint
Gluteus maximus extends hip joint
Flexors:
Hamstrings flex knee joint
Iliopsoas flex hip joint
What is this
Tendon
What is this
Tendon sheath:
Dense irregular connective tissue surrounding tendon
What is this
Smooth muscle
What is this
Skeletal muscle
What is this
Cardiac muscle
What is hypertrophy and what is it caused by
Cells increasing in size
Increase in myofibrils – sarcomeres added
Increase in myofilaments
Caused by:
Anabolic factors (building up muscle):
Mechanical load
Steroids (artificial)
Mechanical loading triggers IGF-1 (insulin like growth factor) which stimulates protein synthesis
What is atrophy and what is it caused by
Reduction in muscle volume/mass
Muscles fibres start to shrink
Caused by:
Catabolic factors (breaking down muscle):
Disuse
Denervation
Disease
Malnutrition
What can cause muscle pathology
Injury
Nerve damage
e.g. Stringhalt in horses
Disease
Aging
How are muscle cells repaired
Satellite cells
Activated following damage
Proliferate & differentiate to form muscle cells & daughter cells
- Lost muscle cells
- Clusters of activated satellite cells
- Myotubes form (differentiate into muscle cells)
- Fibres back to normal size
What is polymyositis
Generalised inflammatory myopathy
Muscle damage result of cell-mediated immunity
Treated with corticoid steroids
What is polymyositis
Generalised inflammatory myopathy
Muscle damage result of cell-mediated immunity
Treated with corticoid steroids
What is Masticatory muscle myositis (MMM)
Focal inflammatory myopathy affecting muscle of mastication
Clinical signs include:
Trismus (lock jaw)
Fox like contour of head
Prominence of zygomatic arch
Give example of Congenital & inherited myopathies
e.g. Duchenne Muscular Dystrophy
Humans, dogs & mice
Mutation in gene coding for dystrophin
Severity can vary
Leads to failure of respiratory muscles
