Repolarization in isolated muscle piece fibre proceeds from:
**Core Concept**
Repolarization in isolated cardiac muscle fibers is a critical step in the cardiac action potential, where the membrane potential returns to its resting state. This process involves the inward movement of potassium ions (K+) and the outward movement of sodium ions (Na+) and calcium ions (Ca2+), ultimately resulting in the closure of voltage-gated sodium channels and the opening of potassium channels.
**Why the Correct Answer is Right**
The correct answer involves the understanding of the ionic movements during repolarization. The potassium channels open, allowing K+ ions to flow out of the cell. This is facilitated by the activation of the sodium-potassium pump, which helps to maintain the resting membrane potential. The inward movement of Ca2+ ions is also crucial, as they help to stabilize the membrane potential and promote the closure of voltage-gated sodium channels. The correct answer is: **Option D: Potassium repolarization, facilitated by sodium-potassium pump and calcium ion stabilization.**
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately describe the ionic movements during repolarization. While sodium ions are involved in the action potential, their outward movement is not the primary mechanism of repolarization.
* **Option B:** This option is incorrect because it is a partial description of the action potential, but it does not specifically address the repolarization phase.
* **Option C:** This option is incorrect because it is a misnomer; the "sodium repolarization" is not a recognized term in electrophysiology.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that repolarization is a critical phase of the cardiac action potential, and any disruption to this process can lead to arrhythmias and other cardiac abnormalities.
**Correct Answer: D. Potassium repolarization, facilitated by sodium-potassium pump and calcium ion stabilization.**