The pathway by which action potentials from the sinoatrial node travel through t

The autorhythmicity of the pacemaker cells of the sinoatrial node points to the intrinsic ability of those cells to generate action potentials. Once initiated, the action potentials travel in a wave along the atria from cell to cell, stimulating them to contract. That wave reaches the atrioventricular node, where the speed ( velocity) with which the action potential travels slows dramatically. The atrioventricular node is the only pathway for the action potential to travel from atria to ventricle. This slowing of the action potential allows the ventricle more time to fill before its contractile cycle is initiated. Thus, the contraction of the atrium provides the last chance to fill the ventricles before their contraction begins. After traversing the atrioventricular node, the action potential gains speed as it travels along the bundle of His and bifurcates into the left and right bundle branches. These branches move the action potential toward the apex of the heart before the conduction pathway further branches and ultimately ends at the Purkinje fibers. It is these fibers that transmit the action potential to the ventricular myocyte. The contraction of the ventricle originates at its apex, pushing blood up and out of the ventricle.