Muscles and Contraction Flashcards
Striated Muscle
Under microscope: clear striations running across muscle fibre
e.g. skeletal muscle
cardiac muscle
Smooth muscle
No clear structure
Smooth / plain muscle
around hollow organs
Isotonic contraction
muscle develops tension and the muscle shortens
Isometric contraction
Muscle develops tension but doesn’t shorten
Skeletal muscle
Consists of muscle fascicles
muscle fibres plus connective tissue wrappings
Myofibrils
contractile elements composed of bundles of myofilaments
Muscle fibre
Elongated
Striated
contains lots of myofibrils
Sarcomere
Functional contractile unit of striated muscle
Composed of myofilaments made up of contractile proteins
Light and dark bands at intervals of 2.2um
Made up of actin and myosin
Contractile proteins: Thick Filament
Bundle of myosin
Each molecule has ATP bound to head
Contractile proteins: Thin filament
2 strands of F-actin with regularly spaced Ca2+ regulatory proteins,
Troponin and Tropomyosin
Cross-Bridge cycle
1) rise of Ca2+ in cell = ATP hydrolysis
Cross bridge between actin & myosin
2) Cross bridge moves, muscle contracts
3) New ATP molecule binds to myosin, cross bridge breaks
4) ATP hydrolyses and primes cross bridge
Excitation- contraction coupling
1) AP propagates along surface membrane
2) Depolarisation opens Ca2+ channels
3) Ca2+ released into sarcoplasm, concn rises
4) Ca2+ binds to troponin and contracts muscle
5) Ca2+ reaccumulated by SR via Ca2+ pump and muscle relaxes
Slow Type I muscle fibres
Fatigued slowly Oxidative capacity high Glycolytic capacity Low Capillary density High Motor nerve conduction rate Low
Fast type 2 muscle fibres
Fatigue rapidly Oxidative capacity low glycolytic capacity high capillary density low motor nerve conduction rate high
Neuromuscular junction
Myelinated motor nerve branches at its terminal and each axon ends on a separate muscle fibre
Ending is motor end plate at skeletal muscle fibre
At motor end plate, nerve action potential activates the muscle fibre by releasing ACh
