Heart muscle cells have autorhythmicity meaning that the cells depolarized on their own. What is it about the ion channels in the cells that causes this to happen? 23. What is the function of the pacemaker nodes (SA and AV) and bundle branches in maintaining heart rhythm? Where are each of these structures located. Which one initiates the wave of depolarization across the atria. How does the depolarization wave get from the atria to the ventricles? Be able to describe the sequence that the each of the above structures is activated during the depolarization wave (i.e. Which is 1st, 2nd, 3rd etc.). What parts of the heart contract as the wave passes them and in what order? 24. What parts of the autonomic nervous system control heart rate and what effect does each have on it?