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: acetylcholine binds to receptors on the muscle cell. Vesicle fuses and releases acetylcholine The action potential travels deep into the muscle fiber in the t-tubules. 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 2 Action Potential: Put the stages in order starting at resting potential -70mV 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. Hyperpolarization: The membrane temporarily becomes more negative than the resting potential 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 The ATP is hydrolyzed, the myosin head to return to its original position (cocked position). Calcium ions are released from sarcoplasmic reticulum Cycle repeats leading to further muscle contraction. Nerve impulse reaches the muscle fiber Myosin head pivots, pulling the actin filament inward causing muscle contraction. Myosin heads (on thick filaments) bind to the exposed sites on actin, forming cross-bridges. A new ATP molecule binds to the myosin head, causing it to detach from actin. Tropomyosin shifts exposing the myosin-binding sites on actin Relaxation: nerve signal stops, calcium pumped back into SR, binding site covered, muscle relaxes. Calcium binds to troponin on the thin filament causing shape change.
