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Sarcoplasmic Reticulum
Skeletal Muscle Fiber

Sarcoplasmic Reticulum

Reticulum sarcoplasmicum

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Quick Facts

The sarcoplasmic reticulum is a special form of smooth endoplasmic reticulum found in association with the T tubules in the sarcoplasm of striated muscle and comprising a system of cisternae and tubules forming a plexus around each myofibril. It contains large numbers of calcium pumps and ryanodine receptors and is a storage compartment for calcium ions, which it releases in response to an action potential in the adjacent T tubule to cause muscular contraction (Dorland, 2011).

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Related parts of the anatomy


The sarcoplasmic reticulum (SR) is an organelle that consists of a network of loose flattened tubules with various compartments, many of which contain Ca2+. The two ends of the SR are wider, thus form terminal sacs called cisternae. Two cisternae of adjacent sarcoplasmic reticula and one transverse tubule form a functional unit called a triad, which operates to elicit the release of Ca2+ from SR stores (Maclennan and Zvaritch, 2011).

Key Features/Anatomical Relations

Sarcoplasmic reticulum is a specialized type of smooth endoplasmic reticulum found in skeletal muscle. It forms a network of tubules that extend through a muscle fiber. The flattened tubules surround, but do not make direct contact with the myofibrils in a muscle fiber.


The sarcoplasmic reticulum functions as an intracellular calcium store. Depolarization of the sarcoplasmic reticulum membrane results in the release of calcium ions (Ca2+). This release of calcium ions triggers the cascade required for contraction.

List of Clinical Correlates


—Central core disease


Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.

Maclennan, D. H. and Zvaritch, E. (2011) 'Mechanistic models for muscle diseases and disorders originating in the sarcoplasmic reticulum', Biochim Biophys Acta, 1813(5), pp. 948-64.

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