A pacemaker, which depolarizes spontaneously, establishes the rate of contraction of the heart muscle. The most common pacemaker of the heart is called the AV node. O establishes a resting heart rate of about 60 to 80 contractions per minute. O functions also under the control of both the sympathetic and the parasympathetic nervous systems. O is located in the muscle of the left atrium. O Two of the above are true.
