**Core Concept**
The body maintains a delicate balance of potassium (K+) and sodium (Na+) concentrations across cell membranes, with K+ primarily inside cells and Na+ in the extracellular fluid. This balance is crucial for proper nerve and muscle function. An increase in external K+ concentration can disrupt this balance, leading to various physiological effects.

**Why the Correct Answer is Right**
An increase in external K+ concentration can lead to depolarization of the cell membrane, as K+ ions rush into the cell. This can trigger an action potential in excitable cells, such as neurons and muscle cells. The depolarization can also activate various voltage-gated channels, including calcium channels, leading to an influx of calcium ions into the cell. This can result in muscle contraction and potentially lead to tetany or muscle cramps.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided.
**Option B:** This option is not provided.
**Option C:** This option is not provided.

**Clinical Pearl / High-Yield Fact**
In the setting of hyperkalemia (elevated K+ levels), it's essential to remember that cardiac arrest can occur due to the potentially life-threatening effects of K+ on cardiac membranes. The ECG changes associated with hyperkalemia can progress from peaked T waves to a sine-wave pattern, ultimately leading to cardiac arrest.

**Correct Answer:** Not provided in the original question.