Use Models 1-4 to put the following events in order from the signal from the brain reaching a muscle to the contraction of the whole muscle. •Myosin bends in two places, releasing ADP and pulling on the thin filament.
•The nerve impulse reaches the end of the nerve and causes it to release acetylcholine (Ach)
•An electrical impulse travels down a nerve fiber
•The Z-lines are pulled closer together and the A-band shrinks
•Ach bonds to receptors on the muscle cell membrane and causes the electrical impulse to be transmitted to the muscle cell
•Calcium ions bind to troponin causing it to rotate
•The myofibril gets shorter (contracts)
•The electrical impulse inside the muscle cell causes the release of calcium ions from the endoplasmic reticulum
•Rotation of troponin move tropomyosin off of the myosin binding site on actin
•The myosin head binds the myosin binding domain of actin