Muscular and nervous excitability is reduced by

Options

A. `Na^(+)`
B. `K^(+)`
C. `Ca^(2+)`
D. `Mg^(2+)`.

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks which ion reduces muscular and nervous excitability. Excitability refers to the ability of muscle and nerve cells to respond to stimuli.

2. **Identifying Relevant Ions**: The primary ions involved in muscular and nervous functions are sodium (Na+), potassium (K+), calcium (Ca2+), and magnesium (Mg2+). Each of these ions plays a role in the excitability of muscles and nerves.

3. **Analyzing Potassium Ions**: Potassium ions (K+) are known to have a significant impact on the excitability of both muscle and nerve cells. High levels of potassium can lead to a decrease in excitability, as they help to stabilize the resting membrane potential of cells.

4. **Example of Potassium's Role**: An example is provided regarding dental sensitivity. Potassium nitrate is often used in toothpaste to reduce sensitivity. It works by affecting the nerve endings and reducing their excitability, which is analogous to its effect on muscle and nerve cells.

5. **Conclusion**: Based on the analysis, potassium ions are identified as the ions that reduce muscular and nervous excitability. Therefore, the correct answer to the question is potassium ions.

**Final Answer**: Potassium ions (K+) reduce muscular and nervous excitability.

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