Final answer:
The heart's internal pacemaker is the sinoatrial (SA) node. It has the highest rate of depolarization and establishes the rhythm for heart contractions. The atrioventricular node has the slowest rate of firing in the conduction system.
Step-by-step explanation:
The heart's internal pacemaker is known as the sinoatrial (SA) node. Located in the right atrium, the SA node has the highest inherent rate of depolarization. It initiates the electrical pattern for the contraction of the heart, commonly known as the sinus rhythm. When considering the components of the heart's conduction system and their rate of firing, the atrioventricular (AV) node has the slowest rate of firing. The heart's electrical system functions in a sequence, starting with the SA node, which causes the atria to contract. The impulse then moves to the AV node, experiencing a brief pause, before progressing through the atrioventricular bundle (Bundle of His), then to the bundle branches, and finally spreading to the ventricles via the Purkinje fibers.