Part A - Sequence of Events During Excitation-Contraction Coupling The conversion of an action potential (AP) generated by a motor neuron to contraction of skeletal muscle fiber is called excitation-contraction coupling. This activity will test your understanding of the sequence of events that occur during excitation-contraction coupling. Place the events that occur during excitation-contraction coupling in the correct order from left to right. View Available Hint(s)

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To understand the sequence of events during excitation-contraction coupling in skeletal muscle fibers, we can outline the key steps involved. Here’s the correct order of events:

1. **Action Potential Generation**: An action potential (AP) is generated in the motor neuron and travels down its axon.

2. **Neurotransmitter Release**: The AP reaches the neuromuscular junction, causing the release of acetylcholine (ACh) from the motor neuron into the synaptic cleft.

3. **ACh Binding**: ACh binds to receptors on the muscle fiber's sarcolemma (cell membrane), leading to depolarization of the muscle fiber.

4. **Propagation of Action Potential**: The depolarization triggers an action potential in the muscle fiber, which propagates along the sarcolemma and down the T-tubules.

5. **Calcium Release**: The action potential traveling down the T-tubules causes the sarcoplasmic reticulum to release calcium ions (Ca²+) into the cytosol of the muscle fiber.

6. **Calcium Binding**: Calcium ions bind to troponin, causing a conformational change that moves tropomyosin away from the myosin-binding sites on actin filaments.

7. **Cross-Bridge Formation**: Myosin heads attach to the exposed binding sites on actin, forming cross-bridges.

8. **Power Stroke**: The myosin heads pivot, pulling the actin filaments toward the center of the sarcomere, which results in muscle contraction.

9. **Detachment**: ATP binds to myosin, causing it to detach from actin, and the cycle can repeat as long as calcium and ATP are available.

10. **Calcium Reuptake**: When the stimulation stops, calcium ions are pumped back into the sarcoplasmic reticulum, leading to muscle relaxation.

This sequence outlines the critical steps involved in excitation-contraction coupling in skeletal muscle fibers. If you have specific events or terms you need to place in order, please provide them, and I can assist further!
Here is the correct order of events during excitation-contraction coupling in skeletal muscle fibers: 1. **Action Potential Generation**: An action potential is generated in the motor neuron. 2. **Neurotransmitter Release**: Acetylcholine (ACh) is released into the synaptic cleft. 3. **ACh Binding**: ACh binds to receptors on the muscle fiber. 4. **Depolarization**: This causes the muscle fiber to depolarize. 5. **Action Potential Propagation**: The depolarization spreads along the sarcolemma and T-tubules. 6. **Calcium Release**: The T-tubules trigger the sarcoplasmic reticulum to release calcium ions. 7. **Calcium Binding**: Calcium binds to troponin, changing the position of tropomyosin. 8. **Cross-Bridge Formation**: Myosin heads attach to actin filaments. 9. **Power Stroke**: Myosin heads pull actin filaments, causing muscle contraction. 10. **Calcium Reuptake**: Calcium is pumped back into the sarcoplasmic reticulum, leading to muscle relaxation. This sequence ensures that the muscle fiber contracts in response to the action potential.

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