Sinoatrial Node SAN

These specialised conduction cells are distributed throughout the heart forming specialised conduction pathways (Fig. 1.5). Depolarisation occurs in the Sinoatrial node (SAN). This is a collection of self-excitory (pacemaker) cells that normally fire at a rate of between 60 and 100 Beats Per Minute (BPM). The wave of Depolarisation moves from the SAN through an intra-atrial tract called Bachmanns bundle into the left atrium and to the Atrioventricular (AV) node. From here the impulse travels down the bundle of His into the right and Left bundle branches and finally into the Purkinje fibres activating the ventricles. 

As discussed previously, the P wave represents the depolarisation of both the left and right atria. The initial half of the P wave represents depolarisation of the right atria as the electrical impulse travels from the Sinoatrial node (SAN) to the right atrium and then the left. The impulse reaches the Atrioventricular node (AV) at the... 

FIGURE 7.14 Time-course of G-protein-mediated activation of GIRK potassium channels in rabbit sinoatrial node cells, (a). Outward current evoked by a 33-msec, 50-nA iontophoretic pulse of acetylcholine (between arrows), (b). Response of the unclamped cell to an iontophoretic pulse of acetylcholine (ACh). (Record (a) is adapted with permission from Trautwein et al., in Drug Receptors and Their Effectors, Birdsall, N. J. M., Ed., Macmillan, New York, 1980, pp. 5-22 record (b) is adapted with permission from Noma, in Electrophysiology of Single Cardiac Cells, Noble, D. and Powell, T., Eds., Academic Press, San Diego, CA, 1987, pp. 223-246.)... 

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