Title: Cardiac muscle - Wikipedia
Headings: Cardiac muscle
Cardiac muscle
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Contents
Structure
Gross anatomy
Microanatomy
Cardiac muscle cells
T-tubules
Intercalated discs
Fibroblasts
Extracellular matrix
Physiology
Regeneration
Differences between atria and ventricles
Clinical significance
See also
References
External links

Content: They are continuous with the cell membrane, are composed of the same phospholipid bilayer, and are open at the cell surface to the extracellular fluid that surrounds the cell. T-tubules in cardiac muscle are bigger and wider than those in skeletal muscle, but fewer in number. In the centre of the cell they join together, running into and along the cell as a transverse-axial network. Inside the cell they lie close to the cell's internal calcium store, the sarcoplasmic reticulum. Here, a single tubule pairs with part of the sarcoplasmic reticulum called a terminal cisterna in a combination known as a diad. The functions of T-tubules include rapidly transmitting electrical impulses known as action potentials from the cell surface to the cell's core, and helping to regulate the concentration of calcium within the cell in a process known as excitation-contraction coupling. Intercalated discs
Main article: Intercalated disc
Intercalated discs are part of the cardiac muscle sarcolemma and they contain gap junctions and desmosomes. The cardiac syncytium is a network of cardiomyocytes connected by intercalated discs that enable the rapid transmission of electrical impulses through the network, enabling the syncytium to act in a coordinated contraction of the myocardium. There is an atrial syncytium and a ventricular syncytium that are connected by cardiac connection fibres.