Which ion causes repolarization –
**Core Concept**
The repolarization of cardiac cells is a critical phase of the cardiac action potential, allowing the heart to return to its resting state. This process involves the movement of ions across the cell membrane, ultimately leading to the restoration of the resting membrane potential.
**Why the Correct Answer is Right**
Repolarization is primarily caused by the efflux of potassium ions (K+) out of the cell, driven by the potassium channels. As the action potential reaches its peak, the rapid influx of sodium ions (Na+) and calcium ions (Ca2+) ceases, and the potassium channels open, allowing K+ to flow out of the cell. This movement of K+ ions back into the extracellular space contributes to the repolarization of the cardiac cell membrane.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is likely a distractor and does not have a direct relation to repolarization.
* **Option B:** Chloride ions (Cl-) play a role in the cardiac action potential, particularly in the plateau phase, but are not primarily responsible for repolarization.
* **Option C:** Sodium ions (Na+) are involved in the initial depolarization phase of the cardiac action potential, but their movement is not responsible for repolarization.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the movement of potassium ions during repolarization is crucial for the restoration of the resting membrane potential and the preparation of the cardiac cell for the next action potential.
**Correct Answer: C. Potassium ions (K+).**