Cardiac pacemaker controls the rate of contraction for the entire heart muscle because its cells have the quickest rate of spontaneous depolarization, thus they initiate action potentials the quickest. The action potential generated by the SA node passes down the electrical conduction system of the heart, and depolarizes the other potential pacemaker cells (AV node) to initiate action potentials before these other cells have had a chance to generate their own spontaneous action potential, thus they contract and propagate electrical impulses to the pace set by the cells of the SA node. This is the normal conduction of electrical activity in the
Purkinje fibers the nucleus causes Purkinje fibers to appear, on a slide, lighter and larger than their neighbors, arranged along the longitudinal direction (parallel to the cardiac vector). They are often binucleated cells. Heart rate is governed by many influences from the autonomic nervous system. The Purkinje fibres do not have any known role in setting heart rate unless the SA node is compromised. They are influenced by electrical discharge from the sinoatrial node. During the ventricular contraction portion of the cardiac cycle, the Purkinje fibres carry the contraction impulse from both the left and right bundle branch to the myocardium of