outside of neuron
Nat Cl Ca Kt
inside of neuron
cat Kt
Figure 5.2. Relative ion concentrations inside and outside a nerve cell, repre-
sented by the relative sizes of the chemical symbols of the ions.The result of all this pumping, pumping, pumping of Na out of
the cell and pumping, pumping, pumping of K into the cell is that
the concentration of Na outside of the cell is greatly increased rela-
tive to the inside and the concentration of K inside the cell is greatly
increased relative to the outside. Other pumps, channels, and ion-
exchanger proteins influence the movement of calcium (Ca*) and
chloride (Cl-) ions across the membrane. Thus, the concentrations
of these various ions inside and outside the nerve cell are different,
with Nat, Cat, and Cl more concentrated outside than inside, and K*
more concentrated inside than outside (Fig. 5.2).
Because ions carry electric charge, the concentration differences
result in electric-charge differences between the inside and outside of