The following is the correct muscle contraction sequence:

(i) Acetylcholine ( released at the synaptic terminal diffuses across the synaptic cleft and binds to receptor proteins on the muscle fiber's plasma membrane, triggering an action potential in the muscle fiber.

(ii) The action potential is propagated along the plasma membrane and down tubules.

(iii) The action potential triggers release from the SR.

(iv) Calcium ions bind to troponin in the thin filament: myosin-binding sites are exposed.

(iv) Cycles of myosin cross-bridge formation and breakdown, coupled with ATP hydrolysis, slide the thin filament toward the center of the sarcomere.

(v) After the action potential ends, cytosolic is removed by active transport into the .

(vi) Once cytosolic is removed, tropomyosin again blocks the myosin-binding sites. Contraction ends, and the muscle fiber relaxes.