Put the following events of excitation-contraction coupling in the correct order.
- Calcium ions bind to troponin molecules on the actin myofilaments
- A nerve impulse causes ACh to be released at a neuromuscular junction
- The heads of myosin myofilaments bind to sites on the actin myofilaments, forming cross-bridges
- Calcium ions are released into the sarcoplasm
- The troponin-tropomysin complex moves, exposing active sites on the actin myofilaments
- The T tubules carry the action potential to the interior of the muscle fiber