Sacroplasmic reticulum
The Sarcoplasmic Reticulum (SR) is present in all types of muscle cell (cardiac, smooth and skeletal) and is a form of modified edoplasmic reticulum.[1] It contains an essential store of Ca2+ ions; when the SR is stimulated these ions are released to initiate a contration in the muscle. In other words, the sarcoplasmic reticulum regulates the intracellular concentration of calcium ions.[2]
In cardiac and skeletal muscle cells the SR surrounds the myofibril and release their Ca2+ ions at areas known as terminal cisternae. Terminal cisternae are the part of the sarcoplasmic reticumlum nearest T-tubules. Skeletal and cardiac sarcoplasmic reticulums are similar in this way; however cardiac cells SRs are undeveloped and less dense in comparisson to skeletal cells.[3]
Smooth muscle cells also contain a sarcoplasmic reticulum that extends throughout the cell, in contrast to the other muscle types though, smooth muscles do not contain T-tubules and instead have junctional regions of the sarcoplasmic reticulum that abut areas of the sarcolema or caveolae.[4] Furthermore, Ca2+ ions are not only released from the SR in smooth muscle cells but also come from the extracellular fluid during musclular contraction.[5]
References
- ↑ D.U. Silverthorn, 2010, Human Physiology An Integrated Approach, 5th Edition, Sanfrancisco, Pearson. Page 408
- ↑ B. M. Koeppen & B. A. Stanton, 2008, Berne & Levy Physiology, 6th Edition, Canada: Mosby Elesevier. Page 234.
- ↑ B. M. Koeppen & B. A. Stanton, 2008, Berne & Levy Physiology, 6th Edition, Canada: Mosby Elesevier. Page 258
- ↑ B. M. Koeppen & B. A. Stanton, 2008, Berne & Levy Physiology, 6th Edition, Canada: Mosby Elesevier. Page 271.
- ↑ D.U. Silverthorn, 2010, Human Physiology An Integrated Approach, 5th Edition, Sanfrancisco, Pearson. Page 434.