What is the path of the action potential through the electrical conducting system of the heart?

Answer 1

Impulses are sent normally from the SA node through the atria, across to the ventricles through the AV node, and spread throughout the ventricles by the HIS bundle and then the Purkinje Fibers:

SA node>>(atria)>>AV node>>HIS bundle>>Purkinje Fibers>>(venticles)

Each part of this conduction path is capable of firing its own impulses without any outside influence. Meaning if you took the heart out of the body and gave it nutrients (ATP), it would beat like normal. However, the firing rate differs in each section, generally decreasing from left to right. However, under normal conditions, since the SA node fires the fastest (about 100 times per second), this overrides all the other intrinsic firing capabilities.

During venticular fibrillation, for some reason the ventricles fire at their own intrinsic rate, which is out of synch with the rest of the heart, and this if not immediately treated with defibrillation will result in death.

As for normal resting heartrate, youll notice I said the SA node fires at 100 beats per second, yet human heartrate at rest is much closer to 70 beats per second. This is because the SA node is under autonomic nervous control. The sympathetic system increases firing above the normal 100 beats/min, and the parasympathetic nervous system decreases it to about 70 beats/min. What does this mean? It means that during normal resting state, parasympathetic control dominates heartbeat.