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level: 15.8 Contraction of skeletal muscle

Questions and Answers List

level questions: 15.8 Contraction of skeletal muscle

QuestionAnswer
Antagonistic muscles and how they work- Skeletal muscle works in antagonistic pairs - These pairs pull in opposite directions + when 1 is contracted + the other is relaxed - Muscles cannot push they can only pull
When a muscle contracts what changes occur to the sacromere- The I-band becomes narrower - The Z-lines move closer together or in other words the sacromere shortens - The H-zone becomes narrower - A band = remains the same
3 main proteins that are involved in the sliding filament mechanism- Myosin - Actin - Tropomyosin
Myosin- Made up of 2 types of protein - A fibrous protein filament (tail) - A globular protein formed into 2 bulbous structures at 1 end (the head)
Actin- Globular protein arranged into a helical strand
Tropomyosin- Fibrous strand wound around actin filaments
SFM - Muscle stimulation (1)- An AP travels into the muscle fibre via T-tubules, which are in contact with the SR - As AP reaches the SR, cal ions channels open - Cal ions diffuse into SR
SFM - Muscle stimulation (2)- Cal ions released from SR, binds to troponin - Causes tropomyosin mol to move, exposing myosin binding site on actin filament - Now myosin + actin can bind to form cross-bridge
SFM - Muscle contraction (1)- Myosin head attaches to actin to form a cross bridge (calcium ions must be present)
SFM - Muscle contraction (2)- ADP + Pi are released from the myosin - This causes a POWER STROKE (ACTIN slides past)
SFM - Muscle contraction (3)- ATP binds to the myosin head causing the cross bridge to release
SFM - Muscle contraction (4)- ATP is broken to ADP + Pi - This energy release cocks the myosin head (recovery stroke)
SFM - Muscle relaxation- Ca2+ absorbed back into the SR - Tropomyosin reverts to orginal shape, blocks actin binding sites - Contraction stops
Phosphocreatine- Cannot supply energy directly to the muscle - Supplies phosphate, which is available immediately to combine w/ADP + so reform ATP - Store is replenished using phosphate from ATP when muscle is relaxed
Roles of tropomyosin and calcium ions- Ca2+ causes tropomyosin to be displaced - So it no longer blocks the myosin binding site - So myosin and actin can bind together allowing bridge cycling
Role of ATP- Needed to actively transport Ca2+ into tropomyosin - When the muscle relaxes Ca2+ are actively transported back into the sacroplasmic reticulum (need ATP) - Binds to myosin head causing it to detach, hydrolysed into ADP+Pi causing cock and attach of myosin head