The flow of ionic electric current along cell membranes can only extend over a short distance, but it causes a graded change in the local membrane potential. A graded membrane potential is a change from the resting potential that is proportional to the magnitude of a stimulus. That stimulus can be chemical or mechanical. Graded potentials are a means of integrating stimuli because the membrane can respond with proportional amounts of depolarization or hyperpolarization to each stimulus, and those changes in membrane potential are summed. In the next chapter you will learn how graded potentials play important roles in sensory systems. However, the spread of graded potentials can only be local and cannot be transmitted down long axons. Therefore axons code information as discrete APs that travel along their membranes. Graded potentials, however, play an important role in the generation of APs.