Membrane potential of a cell forms

Options

A. movement of anions into the cell
B. Movement of cations into the cell
C. Action of proton pumb
D. Action of an electrotgenic pumb

Answer

### Step-by-Step Solution:

1. **Understanding Membrane Potential**:
- The membrane potential of a cell refers to the difference in electric charge across the cell membrane. This is primarily due to the distribution of ions inside and outside the cell.

2. **Identify Intracellular and Extracellular Environments**:
- The intracellular environment refers to the space within the cell, while the extracellular environment refers to the space outside the cell.

3. **Dominant Ions Inside and Outside the Cell**:
- The dominant ion inside the cell is potassium (K+), while sodium (Na+) is the dominant ion outside the cell.
- Although sodium is present inside the cell, its concentration is significantly lower compared to potassium.

4. **Normal Range of Membrane Potential**:
- The typical membrane potential of a cell ranges from -40 to -70 millivolts (mV). This negative value indicates that the inside of the cell is more negatively charged compared to the outside.

5. **Depolarization and Ion Movement**:
- When a cell is excited (depolarized), sodium ions move into the cell while potassium ions move out. Specifically, for every 3 sodium ions that are pumped out, 2 potassium ions are pumped in.

6. **Role of the Sodium-Potassium Pump**:
- The movement of sodium and potassium ions occurs via the sodium-potassium pump, which actively transports these ions against their concentration gradients. This process requires ATP (energy).

7. **Effect on Membrane Potential**:
- As a result of the sodium-potassium pump, the inside of the cell becomes more negatively charged (due to the higher concentration of potassium) while the outside becomes more positively charged.

8. **Conclusion on Cation Movement**:
- The overall movement of cations (positively charged ions) is crucial for establishing and maintaining the membrane potential. In this case, sodium is moving out of the cell and potassium is moving into the cell.

### Final Answer:
The membrane potential of a cell forms due to the movement of cations (sodium and potassium ions) across the cell membrane, primarily facilitated by the sodium-potassium pump.

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