Title: Cardiac excitation-contraction coupling - Wikipedia
Headings: Cardiac excitation-contraction coupling
Cardiac excitation-contraction coupling
Contents
Initiation
Calcium-induced calcium release
Muscle Contraction
Termination of contraction
Heart rate
References

Content: This is important as it means that once the atria have contracted, there is a slight delay which enables the ventricles to fill with blood before they contract. Calcium-induced calcium release
Certain regions of the sarcolemma penetrate deep into the cell. These are known as transverse-tubules (t-tubules); which are also found in skeletal muscle cells) and allow for the action potential to travel into the centre of the cell. Special proteins called L-type calcium channels (also known as dihydropyridine receptors (DHPR)) are located on the t-tubule membrane, and are activated by the action potential. Activated DHPR’s open, forming a channel, that allows Ca 2+ to pass into the cell. This increase in Ca 2+, then binds to and activates another receptor, called a type 2 ryanodine receptor (RyR2), located on the membrane of a structure known as the sarcoplasmic reticulum (SR). The SR is a Ca 2+ store within the cell and is located very close to the T-tubule. Activation of RyR2 causes it to open, releasing even more Ca 2+ into the cell, this release of calcium is called a calcium spark. This means that the initial flow of Ca 2+ into the cell, caused a larger release of Ca 2+ within the cell, therefore the process is called calcium induced calcium release (CICR).