Which of the following statements comparing action potentials and graded potentials is INCORRECT?
a) Spread of a graded potential occurs by passive local current, whereas spread of an action potential occurs by propagation as one depolarized site brings the adjacent site to threshold.
b) The effect of a graded potential diminishes with increasing distance from the site of stimulation, whereas an action potential's effect is constant with distance traveled.
c) Graded potentials occur only in excitable membranes, whereas action potentials occur in most cell membranes. d) Action potentials show an all-or-none phenomenon, but graded potentials do not.