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Content: Cardiac muscle cells contain many mitochondriawhich provide the energy needed for the cell in the form of adenosine triphosphate(ATP), making them highly resistant to fatigue. [ 5][3]
T-tubules[edit]
Main article: T-tubules
T-tubules are microscopic tubes that run from the cell surface to deep within the cell. They are continuous with the cell membrane, are composed of the same phospholipid bilayer, and are open at the cell surface to the extracellular fluidthat surrounds the cell. T-tubulesin cardiac muscle are bigger and wider than those in skeletal muscle, but fewer in number.[5] 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. [ 6]
The functions of T-tubules include rapidly transmitting electrical impulses known as action potentialsfrom 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. [ 5]
Intercalated discs[edit]
Main article: Intercalated disc
Intercalated discs are part of the cardiac muscle sarcolemma and they contain gap junctions and desmosomes.