The resting membrane potential of the cell is maintained due to unequal distribution of ions. The nerve cell membrane is more permeable to potassium ions than the sodium ions.
The selective permeability (or semipermeable) of nerve cell prevent the efflux of anions from the interior of the cell and pumps the sodium ions to the extracellular fluid.
So, the interior of the cell is negatively charged, and it contains high concentrations of K+ ions. The exterior of the cell is positively charged, and it contains high concentrations of sodium ions.
Thus, the blanks can be filled with semipermeable; negative.