Retrieving "Second Messengers" from the archives

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1. Sarcoplasmic Reticulum

   Linked via "second messengers"

   The sarcoplasmic reticulum (SR)/) is a specialized form of the endoplasmic reticulum found in the cytoplasm of striated muscle fibers (skeletal and cardiac muscle cells). Its primary, universally acknowledged function is the sequestration, storage, and regulated release of calcium ions ($\text{Ca}^{2+}$), which are the crucial second messengers initiating muscle contraction via the [sliding filament t…