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Excitation-Contraction Coupling Figure 12-11a Myosin head Myosin thick filament M line Axon terminal of somatic motor neuron Motor end plate Sarcoplasmic reticulum ACh DHP DHP = dihydropyridine L-type calcium channel RyR RyR = ryanodine receptor-channel T-tubule Muscle fiber (a) Initiation of muscle action potential Somatic motor neuron releases ACh at neuromuscular junction. Net entry of Na + through ACh receptor-channel initiates a muscle action potential Troponin Tropomyosin KEY Actin Z disk Na + Ca 2+ 1 2 1 2
Slide 35
Excitation-Contraction Coupling Figure 12-11a, step 1 Myosin head Myosin thick filament M line Axon terminal of somatic motor neuron Motor end plate Sarcoplasmic reticulum ACh DHP DHP = dihydropyridine L-type calcium channel RyR RyR = ryanodine receptor-channel T-tubule Muscle fiber (a) Initiation of muscle action potential Somatic motor neuron releases ACh at neuromuscular junction. Troponin Tropomyosin KEY Actin Z disk Ca 2+ 1 1
Slide 36
Excitation-Contraction Coupling Figure 12-11a, steps 1–2 Myosin head Myosin thick filament M line Axon terminal of somatic motor neuron Motor end plate Sarcoplasmic reticulum ACh DHP DHP = dihydropyridine L-type calcium channel RyR RyR = ryanodine receptor-channel T-tubule Muscle fiber (a) Initiation of muscle action potential Somatic motor neuron releases ACh at neuromuscular junction. Net entry of Na + through ACh receptor-channel initiates a muscle action potential Troponin Tropomyosin KEY Actin Z disk Na + Ca 2+ 1 2 1 2
Slide 37
Excitation-Contraction Coupling Figure 12-11b DHP = dihydropyridine L-type calcium channel RyR = ryanodine receptor-channel Ca 2+ released (b) Excitation-contraction coupling Distance actin moves Myosin thick filament Action potential in t-tubule alters conformation of DHP receptor. DHP receptor opens RyR Ca 2+ release channels in sarcoplasmic reticulum and Ca 2+ enters cytoplasm. Ca 2+ binds to troponin, allowing actin-myosin binding. Myosin heads execute power stroke. Actin filament slides toward center of sarcomere. KEY 3 4 5 6 7 3 4 5 6 7