Editing Action potential (section)

===Cardiac action potentials===
{{Main|Cardiac action potential|Electrical conduction system of the heart|Cardiac pacemaker|Heart arrhythmia}}

[[Image:Ventricular myocyte action potential.svg|thumb|right|220px|Phases of a cardiac action potential. The sharp rise in voltage ("0") corresponds to the influx of sodium ions, whereas the two decays ("1" and "3", respectively) correspond to the sodium-channel inactivation and the repolarizing eflux of potassium ions. The characteristic plateau ("2") results from the opening of voltage-sensitive [[calcium]] channels.|alt=Plot of membrane potential versus time. The initial resting phase (region 4) is negative and constant flowed by sharp rise (0) to a peak (1). The plateau phase (2) is slightly below the peak. The plateau phase is followed by a fairly rapid return (3) back to the resting potential (4).]]

The cardiac action potential differs from the neuronal action potential by having an extended plateau, in which the membrane is held at a high voltage for a few hundred milliseconds prior to being repolarized by the potassium current as usual.<ref name=Kleber group=lower-alpha /> This plateau is due to the action of slower [[calcium]] channels opening and holding the membrane voltage near their equilibrium potential even after the sodium channels have inactivated.

The cardiac action potential plays an important role in coordinating the contraction of the heart.<ref name=Kleber group=lower-alpha>{{cite journal | vauthors = Kléber AG, Rudy Y | title = Basic mechanisms of cardiac impulse propagation and associated arrhythmias | journal = Physiological Reviews | volume = 84 | issue = 2 | pages = 431–88 | date = April 2004 | pmid = 15044680 | doi = 10.1152/physrev.00025.2003 | s2cid = 21823003 }}</ref> The cardiac cells of the [[sinoatrial node]] provide the [[pacemaker potential]] that synchronizes the heart. The action potentials of those cells propagate to and through the [[atrioventricular node]] (AV node), which is normally the only conduction pathway between the [[atrium (heart)|atria]] and the [[ventricle (heart)|ventricles]]. Action potentials from the AV node travel through the [[bundle of His]] and thence to the [[Purkinje fiber]]s.<ref group=note>These [[Purkinje fiber]]s are muscle fibers and not related to the [[Purkinje cell]]s, which are [[neuron]]s found in the [[cerebellum]].</ref> Conversely, anomalies in the cardiac action potential—whether due to a congenital mutation or injury—can lead to human pathologies, especially [[Heart arrhythmia|arrhythmia]]s.<ref name=Kleber group=lower-alpha /> Several anti-arrhythmia drugs act on the cardiac action potential, such as [[quinidine]], [[lidocaine]], [[beta blocker]]s, and [[verapamil]].<ref group=lower-alpha>{{cite journal | vauthors = Tamargo J, Caballero R, Delpón E | title = Pharmacological approaches in the treatment of atrial fibrillation | journal = Current Medicinal Chemistry | volume = 11 | issue = 1 | pages = 13–28 | date = January 2004 | pmid = 14754423 | doi = 10.2174/0929867043456241 }}</ref>