The phase of after depolarization is characterized by:
**Core Concept**
The phase of afterdepolarization refers to a phenomenon that occurs in cardiac myocytes, specifically during the plateau phase of the action potential. Afterdepolarization involves a transient increase in the membrane potential, leading to premature depolarization and potentially arrhythmias. This phase is primarily mediated by the release of calcium ions from the sarcoplasmic reticulum.
**Why the Correct Answer is Right**
Afterdepolarization is characterized by a transient increase in the membrane potential, which is caused by the influx of calcium ions into the cardiac myocyte. This influx of calcium ions leads to a rapid depolarization of the membrane, resulting in a premature contraction of the cardiac muscle. The release of calcium ions from the sarcoplasmic reticulum is triggered by the previous action potential, and the resulting afterdepolarization can lead to arrhythmias, such as torsades de pointes.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately describe the phase of afterdepolarization. Afterdepolarization is a distinct phase that occurs after the peak of the action potential, whereas the plateau phase refers to the period during which the action potential remains relatively stable.
* **Option B:** This option is incorrect because it is not directly related to the phase of afterdepolarization. The plateau phase is characterized by a slow increase in the action potential, whereas afterdepolarization involves a rapid increase in the membrane potential.
* **Option C:** This option is incorrect because it does not accurately describe the underlying mechanism of afterdepolarization. Afterdepolarization is primarily mediated by the release of calcium ions from the sarcoplasmic reticulum, rather than the influx of sodium ions.
**Clinical Pearl / High-Yield Fact**
Afterdepolarization can be triggered by various factors, including digitalis toxicity, hypokalemia, and ischemia. It is essential to recognize the clinical implications of afterdepolarization and to manage underlying conditions that may lead to this phenomenon.
**Correct Answer:** C.