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Muscle Contraction Cycle (12 step)
Step 1 - -Motor neuron sends action potential
(nerve impulse) to the muscle
Step 2 - -acetylcholine (ACh) release from
vesicles on motor neuron
Step 3 - -ACh binds to receptors on muscle
membrane & activates 2nd action potential, now on
muscle
Step 4 - -Action potential opens active
transport pumps of sarcoplasmic reticulum
Step 5 - -Ca+2 floods sarcoplasm, AChE
degrades ACh
Step 6 - -Ca+2 attaches to troponin of TT
complex and changes its shape
Step 7 - -This shape change pulls tropomyosin
away from myosin-binding sites on actin
Step 8 - -ATP attaches to ATP binding site on
myosin crossbridge
Step 9 - -ATP use on myosin head in presence
of Mg+ splits ATP into ADP+P which energizes
myosin head (swings forward)
Step 10 - -P flies off and myosin head binds to
binding site on actin
Step 11 - -ADP is pushed off + myosin head is
de-energized (pulling actin forward) non myosin
swivels back to resting state
Step 12 - -Repeat 8-11 until the Ca+2 comes
off the TT complex
