Question

where are the cells that make up the senatorial node or pacemaker located

Answer 1

There is something called the sinus node, the heart's pacemaker, which is a microscopic bundle of specialized cells that are located in the top right corner of the heart. (if it's that what you mean)

Answer 2

Sino-atrial node would sounds like senatorial node, and it's the pacemaker: R atria is the loc: http://www.daviddarling.info/encyclopedia/S/sinoatrial_node.html