Answer:
The correct chronological sequence is:
3. Acetylcholine binds to receptors on the motor end plate.
1. End-plate potentials trigger action potentials.
2. Transverse tubules bring potentials into the interior of the cell.
4. Ca2+ is released from the sarcoplasmic reticulum.
Step-by-step explanation:
A motor neuron has a long axon that branches out into several extensions when it approaches the muscle. At the end of each branch, the axons are inserted in the muscle fiber surface, composing neuromuscular join. At this point, the ends of each axon are called synaptic button and are situated over a specialized region of the muscle called the end-plate, which contains several indentations called junctional folds. The synaptic button releases acetylcholine, a neurotransmitter that travels through the synaptic cleft to the junctional folds of the muscle membrane and binds to the acetylcholine receptors. This binding produces a depolarization of the cell called an excitatory postsynaptic potential, also known as the end-plate potential. An action potential is initiated as the voltage-gated sodium channels get opened, allowing sodium to get into the cell. The action potential spreads to the rest of the membrane depolarizing it, including the T-tubules. Calcium ions are released from the sarcoplasmic reticulum and initiate contraction when binding to the troponin.