During depolarization, which gradient(s) drive Na+ ions into the cell?

• A. Only the chemical gradient
• B. Only the electrical gradient
• C. Both the electrical and chemical gradients
• D. Neither gradient

Answer: (C)

Verified step by step guidance

1. Understand the concept of depolarization: Depolarization is the process during which the membrane potential becomes less negative (more positive) due to the influx of positively charged ions, such as Na+ (sodium ions). This occurs in excitable cells like neurons and muscle cells.
2. Identify the gradients involved: Gradients refer to differences in concentration (chemical gradient) and charge (electrical gradient) across the cell membrane. The chemical gradient drives Na+ ions from areas of high concentration (outside the cell) to areas of low concentration (inside the cell). The electrical gradient drives Na+ ions toward the negatively charged interior of the cell.
3. Combine the effects of both gradients: During depolarization, both the chemical gradient (high concentration of Na+ outside the cell) and the electrical gradient (negative charge inside the cell) work together to drive Na+ ions into the cell. This is known as the electrochemical gradient.
4. Relate this to the sodium channels: Voltage-gated sodium channels open during depolarization, allowing Na+ ions to flow into the cell down their electrochemical gradient. This influx of Na+ ions contributes to the rapid change in membrane potential.
5. Conclude the reasoning: Since both the chemical gradient and the electrical gradient are responsible for driving Na+ ions into the cell during depolarization, the correct answer is 'Both the electrical and chemical gradients.'