Electrochemical Gradient of Sodium and Potassium Ions in Cells

Compare the electrochemical gradients for sodium and potassium ions, and recall how the membrane potential and concentration gradient for each ion combine to influence its movement across the plasma membrane.

Na+: high concentration of solutes on the outside of the cell. Concentration gradient moves out to in. RMP is negative so electrical gradient is inward. Electrochemical gradient is same direction in and greater K+: high concentration on the inside. Concentration gradient moves out the cell. electrical moves into the cell. Electrochemical gradient is weaker because moves in opposite direction

Sodium and potassium ions have different electrochemical gradients due to differences in their concentration gradients and the membrane potential. The concentration gradient of sodium is higher outside of the cell compared to its inside, with a ratio of approximately 10:1. On the other hand, the concentration gradient of potassium is higher inside the cell compared to its outside, with a ratio of approximately 30:1.

The membrane potential contributes to the electrochemical gradient of both ions. The resting membrane potential of most cells is around -70 mV, which means that the inside of the cell is negatively charged compared to the outside. This membrane potential provides a driving force for positively charged ions such as sodium and potassium to move across the plasma membrane.

In the case of sodium, the combined effect of the concentration gradient and the membrane potential favors the movement of sodium into the cell. This is because the membrane potential is positive outside and negative inside, which attracts the positively charged sodium ions to move towards the negatively charged inside of the cell. However, the concentration gradient is opposing this movement, since there is a higher concentration of sodium outside the cell. Thus, the net movement of sodium across the plasma membrane depends on the balance between these two forces.

In the case of potassium, the combined effect of the concentration gradient and the membrane potential favors the movement of potassium out of the cell. This is because the membrane potential is negative inside and positive outside, which attracts the positively charged potassium ions to move towards the positively charged outside. Also, the concentration gradient supports this outward movement, since there is a higher concentration of potassium inside the cell. Therefore, the two forces work together to drive potassium out of the cell.

In summary, the electrochemical gradient for sodium and potassium ions depends on both the concentration gradient and the membrane potential of the cell. Sodium moves into the cell, while potassium moves out of the cell, due to the differences in their concentration gradients and the membrane potentials.

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