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Myo-ContractionSteps
20 Steps of Muscle Contraction according to Professor Moore
Question | Answer |
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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. |