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: 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. Action potential reaches the axon terminal of the motor nerve. Calcium enters the axon terminal/knob Vesicle fuses and releases acetylcholine 2 Action Potential: Put the stages in order Stimulus: A stimulus causes the neuron to reach a threshold. Hyperpolarization: The membrane temporarily becomes more negative than the resting potential starting at resting potential -70mV Repolarization: Potassium channels open, allowing K+ ions to flow out, returning the membrane potential to a negative value. 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 Myosin heads (on thick filaments) bind to the exposed sites on actin, forming cross-bridges. Calcium ions are released from sarcoplasmic reticulum Cycle repeats leading to further muscle contraction. The ATP is hydrolyzed, the myosin head to return to its original position (cocked position). Nerve impulse reaches the muscle fiber Calcium binds to troponin on the thin filament causing shape change. 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. Tropomyosin shifts exposing the myosin-binding sites on actin Relaxation: nerve signal stops, calcium pumped back into SR, binding site covered, muscle relaxes.
