ABSTRACT
Action potentials are actively regenerated by opening of voltage-dependent ion channels at each point along an unmyelinated axon, or at the nodes of Ranvier in a myelinated one. The direction in which a postsynaptic potential spreads through a dendritic tree is important in determining its amplitude and time course. Fast synaptic potentials originating at distal synapses on the dendritic tree suffer considerable weakening and slowing if they spread passively. Dendrites have voltage-dependent ion channels and under some circumstances can trigger and propagate action potentials. In many types of neuron, action potentials triggered at the axon hillock are propagated not only down the axon, but also sweep over the cell body and invade the dendrites. In pyramidal cell dendrites, back-propagated action potentials are large, long-lasting calcium spikes that are needed to trigger the bursts of axonal sodium action potentials that are part of the normal repertoire of these cells.
