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).
Related parts of the anatomy
Structure
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.
Function
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
—Fatigue
—Central core disease
References
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.
