cardiac action potential

what really is cardiac action potential and how does it work with potassium to lower the heart rate?

Also is SA node conducted through cardiac cells or neurons

[curmudgen]

Here is a video that explains it - http://search.yahoo.com/search;_ylt=Aiw9j_BR1GNT0kxRzgNLa1JG2vAI?p=cardiac+action+potential+animation&fr=my-myy-s&toggle=1&cop=&ei=UTF-8

Na/K pass in and ut of cells to generate a change in the membrane potential...

[curmudgen]

SA node is a group of modified cardiac cells that have an intrinsic beat...the major pathways throughout the heart that distribute the actin potential for the contractions of the heart is via modified cardiac cells - Purkinje fibers  - all of this is under the modification of the ANS, the autonomic nervous system, and hormones such as adrenalin.
previous answer to one of your questions is added below -
http://www.medhelp.org/posts/Heart-Disease/potassium-and-heart/show/1489642