Mediates the voltage-dependent sodium ion permeability of excitable membranes. Assuming opened or closed conformations in response to the voltage difference across the membrane, the protein forms a sodium-selective channel through which Na(+) ions may pass in accordance with their electrochemical gradient (PubMed:10827969, PubMed:11166117, PubMed:28137877). Implicated in the regulation of hippocampal replay occurring within sharp wave ripples (SPW-R) important for memory (PubMed:29867081). Heterooligomer of a large alpha subunit and a smaller beta subunit. Heterooligomer with SCN2B or SCN4B; disulfide-linked. Interacts with NEDD4L. Interacts with CALM. Expressed in brain (at protein level) (PubMed:10827969, PubMed:11166117). Detected in hippocampus, cortex and brain stem (PubMed:10827969). The sequence contains 4 internal repeats, each with 5 hydrophobic segments (S1, S2, S3, S5, S6) and one positively charged segment (S4). Segments S4 are probably the voltage-sensors and are characterized by a series of positively charged amino acids at every third position. Sumoylated at Lys-38. Sumoylation is induced by hypoxia, increases voltage-gated sodium current and mediates the early response to acute hypoxia in neurons. Sumoylated SCN2A is located at the cell membrane. Conditional knockout mice deficient in brain are morphologically and organogenically indistinguishable from their heterozygous littermates. They die perinatally with severe hypoxia and massive neuronal apoptosis, notably in the brainstem. Sodium channel currents recorded from cultured neurons of knockout mice are sharply attenuated. Belongs to the sodium channel (TC 1.A.1.10) family. Nav1.2/SCN2A subfamily.