When talking about action potentials we say that previous neurons caused an action potential in this neuron and that this neuron's action potential caused the same in further neurons.
But what is the origin of the first-ever action potential? Maybe in a living organism, there are no action potentials initially because the brain is always "on" and some part of the brain can always initiate processes in an other. If that is the case then how is the brain turned "on" initially? If not, then how does the first action potential get triggered from the "resting state"?