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) \[ \begin{array}{c}\text { Voltage-sensitive proteins } \\ \text { open } \mathrm{Ca}^{2+} \text { channels }\end{array} \] \( \begin{array}{l}\text { Sarcoplasmic reticulum } \\ \text { releases } \mathrm{Ca}^{2+}\end{array} \)

The event sequence starts when voltage-sensitive proteins open calcium (Ca²⁺) channels in the T-tubules, triggered by the action potential arriving from the motor neuron. Next, this electrical signal stimulates the sarcoplasmic reticulum (SR) to release Ca²⁺ ions into the cytoplasm of the muscle fiber, a critical step for initiating muscle contraction. As these calcium ions circulate, they bind to troponin on the actin filaments, leading to a conformational change that allows myosin heads to attach, pulling on the actin and resulting in muscle contraction! Isn’t it fascinating how a simple electrical impulse can lead to the complex dance of muscle contraction?