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