Which of these needs to happen for a muscle to contract?

Question

Quizplus · Accepted Answer

All of the events listed are necessary for muscle contraction. An action potential is generated in a lower motor neuron, which causes acetylcholine to be released into the presynaptic cleft. Acetylcholine binds to receptors on the muscle cell, which causes the muscle cell to depolarize. This depolarization triggers the release of calcium ions from the sarcoplasmic reticulum, which bind to troponin on the actin filaments. Troponin changes shape, which allows myosin filaments to bind to the actin filaments and pull them towards the center of the sarcomere, causing the muscle to contract.

Which of These Needs to Happen for a Muscle to Contract