Action Potential, Neuromuscular Junction, muscle contractionVersión en línea Action Potential, Neuromuscular Junction, muscle contraction por Dr. David Myers 1 Neuromuscular Junction: Put the stages in order: sodium gates open causing depolarization of the muscle cell Action potential reaches the axon terminal of the motor nerve. The action potential travels deep into the muscle fiber in the t-tubules. Calcium enters the axon terminal/knob acetylcholine binds to receptors on the muscle cell. Vesicle fuses and releases acetylcholine 2 Action Potential: Put the stages in order Back to resting potential Hyperpolarization: The membrane temporarily becomes more negative than the resting potential starting at resting potential -70mV Depolarization: Sodium channels open, allowing Na+ ions to flow into the neuron, making the inside more positive. Stimulus: A stimulus causes the neuron to reach a threshold. Repolarization: Potassium channels open, allowing K+ ions to flow out, returning the membrane potential to a negative value. 3 Sliding Filament Theory: Put the stages in order A new ATP molecule binds to the myosin head, causing it to detach from actin. Calcium binds to troponin on the thin filament causing shape change. Calcium ions are released from sarcoplasmic reticulum Myosin heads (on thick filaments) bind to the exposed sites on actin, forming cross-bridges. Myosin head pivots, pulling the actin filament inward causing muscle contraction. Nerve impulse reaches the muscle fiber Tropomyosin shifts exposing the myosin-binding sites on actin Cycle repeats leading to further muscle contraction. The ATP is hydrolyzed, the myosin head to return to its original position (cocked position). Relaxation: nerve signal stops, calcium pumped back into SR, binding site covered, muscle relaxes.
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