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Myo-ContractionSteps

20 Steps of Muscle Contraction according to Professor Moore

QuestionAnswer
Step 1 Muscle cell (myofiber) stimulation begins with an action potentioal traveling down a somatic motor neuron axon branch to an axon terminal.
Step 2 The action potential stimulates the opening of voltage-gated CA2+ chaneels along the axon terminal membrane, allowing the CA2+ to rush into the axon terminal, down its electrochemical gradient.
Step 3 CA2+ triggers the exocytosis of acetylcholine (ACh) from synaptic vesicles.
Step 4 ACh diffuses across the synapticcleft and binds to ACh-receptors on the motor end plate.
Step 5 Opening of ligand-gated cation channels allowing Na+ influx and K+ efflux.
Step 6 Depolarization of the motor end plate, called an end plate potential.
Step 7 The end plate potential spreads to the sarcolemma surrounding the motor end plate, triggering the opening of voltage-gated Na+ channels.
Step 8 Na+ influx, which depolarizes the sarcolemma, generating an action potential the spreads across the entire sarcolemma and down all of the T-tubules.
Step 9 Depolarization of the cell membrane is followed immediately by repolarization.
Step 10 Depolarization of the T-tubule membrane causes voltage-sensitive T-Tubules to change shape, pulling open adjacent Ca2+ release channels.
Step 11 Ca2+ exists the terminal cisternae, down it's gradient, increasing intracellular.
Step 12 Two Ca2+ ions bind to each Tn-C (troponin subunit), causing troponin to change shape.
Step 13 Troponin moves tropomyosin to expose myosin binding sites on actin.
Step 14 Actin binding site of myosin heads automatically bind to actin, forming cross-bridges.
Step 15 Power stroke occurs as energized myosin heads pivot, moving thin filaments toward the M-line of each sarcomere.
Step 16 ATP binds to myosin ATPase, allowing the myosin head to detach from actin.
Step 17 ATP is hydrolyzed into ADP+Pi, providing the myosin head with potential energy. Myosin head in the high-energy state.
Step 18 Myosin head again binds to actin followed by another power stroke.
Step 19 Another ATP binds to myosin ATPase and the cycle repeats.
Step 20 AchE quickly breaks down ACh and the relaxation period beings.
Created by: brookelise