Significance Under most conditions cortical pyramidal neurons are strongly biased to initiate action potentials in the distal part of the axon initial segment (AIS) rather than in the dendrites, where the excitatory postsynaptic potential amplitude is largest. This feature is widely attributed to the axonal presence of the low-threshold Na ⁺ channel subtype Na _v 1.6. Here, using electrical and high-speed Na ⁺ imaging recordings from Na _v 1.6 null pyramidal neurons, we demonstrate that the presence of this subunit is neither critical for positioning the spike initiation site within the AIS nor for the spike backpropagation to the dendrites. We also find that one of the most important features of axonal Na ⁺ channel kinetics, the lower activation threshold, is not entirely dependent on the Na ⁺ channel subtype.