Editing Endoplasmic reticulum (section)

==== Sarcoplasmic reticulum ====
[[File:Blausen 0801 SkeletalMuscle.png|thumb|left|250px|[[Skeletal muscle]] fiber, with sarcoplasmic reticulum colored in blue]]
{{main|Sarcoplasmic reticulum}}
{{See also |Calcium-induced calcium release}}

The sarcoplasmic reticulum (SR), from the Greek σάρξ ''sarx'' ("flesh"), is smooth ER found in [[muscle cell]]s.  The only structural difference between this organelle and the smooth endoplasmic reticulum is the composition of proteins they have, both bound to their membranes and drifting within the confines of their lumens. This fundamental difference is indicative of their functions: The endoplasmic reticulum synthesizes molecules, while the sarcoplasmic reticulum stores calcium ions and pumps them out into the sarcoplasm when the muscle fiber is stimulated.<ref name="Toyoshima-2000">{{cite journal | vauthors = Toyoshima C, Nakasako M, Nomura H, Ogawa H | title = Crystal structure of the calcium pump of sarcoplasmic reticulum at 2.6 A resolution | journal = Nature | volume = 405 | issue = 6787 | pages = 647–55 | date = June 2000 | pmid = 10864315 | doi = 10.1038/35015017 | bibcode = 2000Natur.405..647T | s2cid = 4316039 }}</ref><ref>{{cite book | first = Steven R | last = Goodman | name-list-style = vanc | title = Medical Cell Biology | edition = 3rd|publisher=Academic Press|pages=69|url=https://books.google.com/books?id=tRbCHk9easQC&q=smooth+er+stores+calcium+ions+muscle+cells&pg=PA69 | isbn = 9780080919317 | date = 2007-11-26 }}</ref> After their release from the sarcoplasmic reticulum, calcium ions interact with contractile proteins that utilize ATP to shorten the muscle fiber. The sarcoplasmic reticulum plays a major role in [[excitation-contraction coupling]].<ref>{{cite book |title = Fundamentals of Anatomy and Physiology |first1 = Frederick |last1 = Martini |first2 = Judi |last2 = Nath |first3 = Edwin |last3 = Bartholomew | name-list-style = vanc |edition = 10th |isbn = 978-0321909077 |year = 2014|publisher = Pearson }}</ref>