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. 2021 May 27;12:669029. doi: 10.3389/fphys.2021.669029

FIGURE 1.

FIGURE 1

The sinoatrial node. (A) Dorsolateral view of the sinoatrial node region of a gelatine-filled mouse heart. (B) Schematic illustration of the heart shown in panel (A), depicting the location of the sinoatrial node (SAN) (gray) within the right atrium (RA). (C, left) Magnification of the SAN region. The cranial portion is referred to as the sinus node “head,” the middle portion as the “body,” and the caudal portion as the “tail.” HCN1 channels are only expressed in the head region whereas HCN4 channels are expressed throughout the whole SAN. (C, right) The SAN is innervated by the sympathetic and parasympathetic nervous system (dashed lines). Activity of both ANS branches tightly controls cAMP concentration in SAN cells. Abbreviations: Ao, Aorta; IVC, inferior vena cava; LCCA, left common carotid artery; LCV, left cranial vein; LSA; left subclavian artery; PA, pulmonary arteries; PV, pulmonary veins; RAA, right atrial appendage; RCCA, right common carotid artery; RSA, right subclavian artery; SVC, superior vena cava. Figure is adapted from Hennis et al., 2021.