Title: Sarcoplasmic reticulum - Wikipedia
Headings: Sarcoplasmic reticulum
Sarcoplasmic reticulum
Contents
Structure
Calcium absorption
Calcium storage
Calcium release
Role in rigor mortis
References

Content: Contents
1 Structure
2 Calcium absorption
3 Calcium storage
4 Calcium release
5 Role in rigor mortis
6 References
Structure
The sarcoplasmic reticulum is a network of tubules that extend throughout muscle cells, wrapping around (but not in direct contact with) the myofibrils (contractile units of the cell). Cardiac and skeletal muscle cells contain structures called transverse tubules (T-tubules), which are extensions of the cell membrane that travel into the centre of the cell. T-tubules are closely associated with a specific region of the SR, known as the terminal cisternae in skeletal muscle, with a distance of roughly 12 nanometers, separating them. This is the primary site of calcium release. The longitudinal SR are thinner projects, that run between the terminal cisternae/junctional SR, and are the location where ion channels necessary for calcium ion absorption are most abundant. These processes are explained in more detail below and are fundamental for the process of excitation-contraction coupling in skeletal, cardiac and smooth muscle . Calcium absorption
The SR contains ion channel pumps, within its membrane that are responsible for pumping Ca 2+ into the SR. As the calcium ion concentration within the SR is higher than in the rest of the cell, the calcium ions won't freely flow into the SR, and therefore pumps are required, that use energy, which they gain from a molecule called adenosine triphosphate (ATP). These calcium pumps are called Sarco (endo)plasmic reticulum Ca 2+ ATPases (SERCA). There are a variety of different forms of SERCA, with SERCA 2a being found primarily in cardiac and skeletal muscle.