Explain the route and role of calcium ions in the Sliding Filament theory of muscle contraction

ROUTE: when an action potential arrives at the neuromuscular junction, Calcium ions are released from the sarcoplasmic reticulum, into the sarcoplasm, where they bind to the troponin molecules on the tropomyosin. After contraction of the muscle fibre, the calcium ions are taken up by the sarcoplasmic reticulum for relaxation of the muscle. ROLE: When the calcium ions bind to troponin, they cause the tropmyosin molecules to move out of the way to expose the myosin binding sites on the actin filament. The abundance of calcium ions in the sarcoplasm regulates the contraction and relaxation of the muscle fibre.