Question

In a neuron at rest, if a large number of Na⁺ channels in the axonal membrane open, Na⁺ will move:

a. From the extracellular fluid into the cytoplasm, down its electrical gradient but against its chemical gradient.

b. From the cytoplasm into the extracellular fluid, down its chemical gradient but against its electrical gradient.

c. From the cytoplasm into the extracellular fluid, down its electrical and chemical gradients.

d. From the extracellular fluid into the cytoplasm, down its electrical and chemical gradients.

e. From the extracellular fluid into the cytoplasm, down its chemical gradient but against its electrical gradient.

Answer 1

d. From the extracellular fluid into the cytoplasm, down its electrical and chemical gradients.

Sodium ion concentration are more at the outside of the cell as compared to inside the cell, this creates an electrochemical gradient , in a living cell, the concentration gradient of Na+ tends to drive it into the cell, and the electrical gradient of Na+ (a positive ion) also tends to drive it inward to the negatively charged interior. This is opposite of sodium potassium pump which actively transports sodium ion against the electrtochemical gradient.