Sarcoplasmic reticulum. Definition. noun. The special type of smooth endoplasmic reticulum found in smooth and striated muscle fibers whose function is to store and release calcium ions.Supplement. The sarcoplasmic reticulum releases calcium ions during muscle contraction and absorb them during relaxation.lease contribute to this project, if you have more information about this term feel free to edit this page. This page was last modified on 18 September 2008, at 09:28.This page has been accessed 284,989 times.