Metabolic Pathways Underlying Muscle Contraction Flashcards
Describe the structure of skeletal muscle
Skeletal muscle, muscle fascicle, muscle fibre, myofibril, sarcomere
What is the muscle fascicle
Bundle of muscle fibres/cells
Up to 150 muscle fibres per fascicle
Surrounded by perimysium
What is the muscle fibre/cell
Abundant with mitochondria
Surrounded by endomysium
Encloses sarcoplasm and myofibrils
What are myofibrils
Surrounded by sarcoplasmic reticulum
Runs parallel to myofibril
Storage site for calcium ions
Releases Ca2+ into sarcoplasm for muscle contraction
What do sarcomeres contain
Actin 42kDa – thin filament
Myosin 480kDa – thick filament
What are the two regulatory proteins
Tropomyosin and troponin
What is the function of troponin
Binds calcium, shifts tropomyosin
What is the function of tropomyosin
Blocks myosin binding site at rest, moves to allow contraction
What are the stages of muscle contraction
ATP binds to the myosin head causing myosin to lose affinity for actin.
Myosin bends with ATP, hydrolyses it, then binds to a new actin subunit.
Pi release triggers a neck shift. “Power stroke” returns myosin to its original shape.
ADP released to complete the cycle.
What is a sarcomere
Basic contractile unit with overlapping actin (thin) and myosin (thick) filaments.
What is the function of myosin
Motor protein, binds actin, uses ATP for force.
What is the function of actin
Provides binding sites for myosin.
What is the function of Ca2+
Ca²⁺ from sarcoplasmic reticulum binds troponin to initiate contraction.
What is the function of ATP
ATP powers myosin action and Ca²⁺ reuptake for relaxation.
Describe neural control of muscle contraction
Nerve signal triggers acetylcholine release at the neuromuscular junction.
Action potential travels via T-tubules, causing Ca²⁺ release and contraction.
