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It has striated myocytes with one or two central nuclei. This tissue occurs only in the heart and presents contraction independent of the individual's will (involuntary contraction).
In the heart muscle this contraction is vigorous and rhythmic.
These muscle cells are smaller and branched, intimately joined together by specialized and typical structures of the cardiac musculature: the intercalated discs, which make the electrical connection between all the heart cells. Thus, if a cell receives a sufficiently strong stimulus, it is transmitted to all other cells and the heart as a whole contracts.
This stimulus transmission is made by channels of water and ions passing between cells, which facilitates the diffusion of the ionic signal between one cell and another, determining the rhythmic wave of cell contraction. The intercalary discs have adhesion structures between cells that hold them together even during the vigorous process of cardiac muscle contraction.
Cardiac muscle cells are capable of self-stimulation, not depending on a nerve stimulus to initiate contraction. The rhythmic contractions of the heart are generated and driven by a network of modified cardiac muscle cells that lie just below the endocardium, the tissue lining the heart internally.
There are numerous nerve endings in the heart, but the nervous system acts only by regulating the heart rate to the body's needs.