Where on a neuron does the action potential start, and why there? · Grey Matter

In most neurons it starts at the axon initial segment, the first few tens of micrometres of axon after the cell body.

Where on a neuron does the action potential start, and why there?

In most neurons it starts at the axon initial segment, the first few tens of micrometres of axon after the cell body. Sodium channels there are packed several times more densely than on the soma, and the low-threshold Nav1.6 subtype concentrates at its far end, so this is where inputs summed from the dendrites first reach threshold. From there the spike runs forward down the axon and also backward into the soma and dendrites, where it tells the synapses that the cell has fired. Because so much depends on this short stretch, inhibitory chandelier cells that target it, and changes in its length or position, have a strong grip on a neuron's output.