Th e main function of the sinus node is to provide the electrical impulse responsible for normal cardiac rhythm. Th e rhythmic coordination depends on the passage of the excitation wave by the heart through its conductive system of impulse. Th ere is considerable variability in the size and exact location of the sinus node of individual hearts even within the same species. Histological features of the sinus node including the cells, the nodal artery, the collagen framework, and the innervation, and also some physiological characteristics of the node, will be discussed.

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