Foundations Of Cognitive Science

Action Potential

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).


  1. Levitan, I. B., & Kaczmarek, L. K. (1991). The Neuron: Cell And Molecular Biology. New York: Oxford University Press.
  2. von Neumann, J. (1958). The Computer And The Brain. New Haven, CN: Yale University Press.

(Added April 2011)