cardiac muscle tissue sinoatrial node http://upload.wikimedia.org/wikipedia/commons/d/d2/Sinoatrial_node_low_mag.jpg http://upload.wikimedia.org/wikipedia/commons/d/de/Sinoatrial_node_2_low_mag.jpg sinuatrial node cardiac pacemaker UBERON:0002351 MA:0000097 sinus node of Keith and Flack Koch's node SA nodal muscle tissue nodus sinuatrialis ZFA:0005069 NCIT:C33555 TAO:0005069 sinuatrial nodal muscle tissue WP:Heart states: "The SA node is found in all amniotes but not in more primitive vertebrates. In these animals, the muscles of the heart are relatively continuous and the sinus venosus coordinates the beat which passes in a wave through the remaining chambers. Indeed, since the sinus venosus is incorporated into the right atrium in amniotes, it is likely homologous with the SA node. In teleosts, with their vestigial sinus venosus, the main centre of coordination is, instead, in the atrium.". Note however that ZFA has SA node. SA node sinu-atrial node OpenCyc:Mx4rOhejDGMcEd2AAABQjYGu0g The part of the cardiac conduction system that controls the timing of heart muscle contraction. It relays electrical signals to the AV node[GO]. Subdivision of conducting system of heart at the junction of the right atrium and the superior vena cava, around the sinoatrial nodal branch of right coronary artery and is continuous with the internodal tract[FMA]. EMAPA:35772 uberon MESH:D012849 sinoatrial node node of Keith-Flack EHDAA2:0004184 sinus node FMA:9477 GAID:561 UMLS:C0037189 BTO:0004358 nodus sinuatrialis