If enough of graded potentials arrive at the neuron’s soma at roughly the same time, then their cumulative effect disrupts the neuron’s resting electrical state. This results in a massive depolarization of the membrane of the neuron's axon, called an action potential, which is a signal of constant intensity that travels along the axon to eventually stimulate some other neuron.
A crucial property of the action potential is that it is an all-or-none phenomenon, representing a nonlinear transformation of the summed graded potentials. The neuron converts continuously varying inputs into a response that is either on (action potential generated) or off (action potential not generated). This has been called the all-or-none law (Levitan & Kaczmarek, 1991). The all-or-none output of neurons is a nonlinear transformation of summed, continuously varying input, and is the reason that the brain can be described as digital in nature (von Neumann, 1958).