Which of these transport processes is the major means by which Na+ is transported across the membrane of neurons? Why?
A) both II and III because the activity of the neuron varies
B) I because Na+ is so small it can freely diffuse into the cell
C) III because Na+ is actively transported out of a neuron to maintain extracellular concentration
D) II because Na+ is charged and cannot cross the hydrophobic interior space of the cell membrane
