Threshold is reached at the axon hillock, and an action potential results. Describe, what happens during the three phases of an action potential. Include these topics: What causes the channels involved in action potentials to open? In what order do they open and close? Which channel(s) inactivate? How is that different from closing? Are voltage-gated channels found throughout the neuron? If not, where are they found? Which channels besides leak channels are open during which phases of the action potential, and in what direction are ions moving through them? Which ion movements are associated with depolarization? With repolarization and hyperpolarization?