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