Action potential curves differ among neurons, cardiomyocytes, and pacemaker cells by their ion influx and efflux patterns. Neurons have a short action potential, cardiomyocytes have a prolonged plateau due to Ca2+ influx, and pacemaker cells exhibit automaticity with a prepotential phase. Each contributes uniquely to the cardiac cycle, as reflected in an electrocardiogram.
To distinguish between the action potential curves of neurons, cardiomyocytes, and pacemaker cells, we must analyze their unique characteristics:
Neurons: Neurons typically have a rapid, all-or-none action potential with a short duration. This is initiated by the rapid influx of Na+ ions, which is followed by the outflow of K+ ions to return the membrane to its resting potential.
Cardiomyocytes: The action potential of cardiomyocytes includes a more prolonged plateau phase due to the influx of Ca2+, which is crucial for muscle contraction. This is followed by the re-establishment of the negative resting membrane potential primarily through the outflow of K+ ions.
Pacemaker cells: Pacemaker cells have a unique prepotential phase reflecting automaticity. This phase involves a slow influx of Na+, followed by a more rapid influx of Ca2+, and ends with the outflow of K+ leading to repolarization.
Relating to the cardiac cycle, the P wave, QRS complex, and T wave on an electrocardiogram (ECG) correspond to atrial depolarization, ventricular depolarization, and ventricular repolarization, respectively. Ions, especially K+ and Na+, are pivotal in terminating the action potentials by pumping out and in through their respective pumps to restore resting potential.
The conducting system of the heart, including the sinoatrial (SA) node, atrioventricular (AV) node, and Purkinje fibers, ensures the proper distribution of electrical impulses. Blocks at any of these points can interrupt the cardiac cycle, potentially leading to cardiac dysfunction.