1. Almost instantaneously, the whole SA node is sending out a strong electrical charge. 2. The SA node is found in all amniotes but not in more primitive vertebrates. 3. Tbx18 transduction converts atrial muscle cells into SA node cells that initiate the heartbeat. 4. These channels allow for continuous rhythmic bursts that control the SA Node of the heart. 5. Pacemaker potentials are fired not only by SA node , but also by the other foci. 6. Retrograde P waves refers to the depolarization from the AV node back towards the SA node . 7. The cause is a gradual lengthening of conduction time from the SA node to the atria. 8. Thus, in the normal, healthy heart, only the SA node intrinsic rate is observable. 9. The superior border of the terminal sulcus designates the transverse plane in which the SA node resides. 10. Conduction across the SA node is normal until the time of the pause when it is blocked.
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