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excitation-contraction coupling

the link between the generation of a action potential (nerve impulse) in the sarcolemma and the start of a muscle contraction

step 1 of excitation-contraction coupling

action potential travels along the sarcolemma

step 1 a of excitation-contraction coupling

causes the release of calcium into the sarcoplasm from the terminal cisternae of the sarcoplasmic reticulum

binds to troponin, which causes tropomyosin to move in between the strands of actin

step 1 b of excitation-contraction coupling

step 1 c of excitation-contraction coupling

exposes the binding sites on the actin

contraction cycle step 1

ATP splits- into ADP (adenosine diphosphate) and a phosphate group

head of myosin attaches to the binding sites (cross bridges)

contraction cycle step 2

contraction cycle step 3

cross bridges flexes (myosin head bends), moving the thin filament toward the middle of the sarcomere, called power stroke

power stroke

contraction cycle step 3

contraction cycle step 4

ATP binds with the myosin head, which releases the myosin head from the actin

energy from ATP is released by splitting, causing the myosin head to return to its original position

contraction cycle step 4 a

contraction cycle step 4 b

myosin is cocked and ready to bind with actin again

relaxation step 1

when nerve impulse stops, release of ACh stops

relaxation step 1 a

calcium is returned to the terminal cisternae-requires energy (ATP)

relaxation step 1 b

when calcium is taken back by the SR, troponin changes shape and tropomyosin once again covers the binding sites on the actin

muscle relaxes

relaxation step 1 c

cycle repeats many times during one contraction of a muscle

relaxation step 1 d


adenosine diphosphate

adenosine triphosphate



neuromuscular junction






the eraser

sarcoplasmic reticulum


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