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Model 5: Neuromuscular junction18. Can muscles contract if there isn’t any free calcium in the cell?a. According to model 5, where is calcium stored inside a muscle cell? b. What causes the calcium to be released from where it is stored? 19. What chemical messenger transmits the electrical impulse between the nerve cell and the muscle cell? Application20. Acetylcholine esterase is an enzyme that degrades Ach in the neuromuscular junction. The nerve gas Sarin blocks this enzyme causing Ach to remain available for binding to the muscle cell receptors. What effect would Sarin gas have on the muscles of your body? As a group, explain why Sarin gas is a deadly poison. [hint: your diaphragm is a muscle]
Exercises1. Use models 5, 4, 3, 2, and 1 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 binds 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