Mechanism
When a neuron fires an action potential, it is initiated at the axon hillock. An action potential spreads down the axon because of the gating properties of voltage-gated sodium channels and voltage-gated potassium channels. However, the cell body or soma can also become depolarized when an action potential is initiated, and this depolarization can spread out to the dendritic tree where there are voltage-gated calcium channels. Voltage-gated calcium channels can then lead to a propagating (most of the time) dendritic action potential. EPSPs from synaptic activation are not large enough to activate the dendritic voltage-gated calcium channels (usually on the order of a couple milliamperes each) so backpropagation is believed to happen only when the cell is activated to fire an action potential.
Read more about this topic: Neural Backpropagation
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