Bachmann's bundle that area. The normal cardiac rhythm originates in the sinoatrial node, which is located in the right atrium near the superior vena cava. From there, the electrical activation spreads throughout the right atrium. There are at least four different locations where the activation can pass to the left atrium. Apart from Bachmann's bundle these are the anterior interatrial septum, posterior interatrial septum, and the coronary sinus. Because it originates close to the sinoatrial node and consists of long parallel fibers, Bachmann's bundle is, during sinus rhythm, the first of these connections to activate the left atrium. Bachmann's bundle In the
Sinoatrial node hyperpolarisation-activated cyclic nucleotide–gated (HCN) channels, are activated. Activation of these channels at very negative membrane potential is an unusual property for ion channels, therefore the flow of sodium (Na) and some potassium (K) through the activated HCN channel is referred to as a "funny current" (I). This funny current causes the membrane potential of the cell to gradually increase, as the positive charge (Na and K) is flowing into the cell. Another mechanism involved in pacemaker potential is known as the calcium clock. Here, calcium is released spontaneously from the sarcoplasmic reticulum (a calcium store) into the cell, this is