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