Cardiac Arrhythmias: Difference between revisions

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===Phase 4: Resting membrane potential===
===Phase 4: Resting membrane potential===
During phase 4 of the action potential intracelullair and extracellulair concentrations of ions are restored. Depending on cell type the resting membrane potential is between -50 to -95 mV. Sinus node and AV nodal cells have a higher resting membrane potential (-50 to -60 mV and -60 to -70 respectively) in comparison with atrial and ventricular cardiomyocytes (-80 to -90 mV). Sinus node cells and AV nodal cells (and to a lesser degree Purkinje fibers cells) have a special voltage dependent channel I<sub>f</sub>, the funny current. Furthermore they lack I<sub>K1</sub>, a K<sup>+</sup> ion channel that maintains the resting membrane potential in atrial and ventricular tissue. The I<sub>f</sub> channel causes a slow depolarization in diastole, called the phase 4 diastolic depolarization, which results in normal automaticity. The frequency of the sinus node discharges are regulated by the autonomous nerve system and due to the relative high firing frequency (60-80 beats per minute) the sinus node dominates other potential pacemaker sites.
During phase 4 of the action potential intracelullar and extracellular concentrations of ions are restored. Depending on cell type the resting membrane potential is between -50 to -95 mV. Sinus node and AV nodal cells have a higher resting membrane potential (-50 to -60 mV and -60 to -70 respectively) in comparison with atrial and ventricular cardiomyocytes (-80 to -90 mV). Sinus node cells and AV nodal cells (and to a lesser degree Purkinje fibers cells) have a special voltage dependent channel I<sub>f</sub>, the funny current. Furthermore they lack I<sub>K1</sub>, a K<sup>+</sup> ion channel that maintains the resting membrane potential in atrial and ventricular tissue. The I<sub>f</sub> channel causes a slow depolarization in diastole, called the phase 4 diastolic depolarization, which results in normal automaticity. The frequency of the sinus node discharges are regulated by the autonomous nerve system and due to the relative high firing frequency (60-80 beats per minute) the sinus node dominates other potential pacemaker sites.


==Cardiac conduction==
==Cardiac conduction==
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