Nav1.1 is expressed in neurons and glia. In neurons, Nav1.1 channels are expressed predominantly in the cell bodies and dendrites, and are presumably involved in propagating synaptic signals from dendrites to soma and in integration of electrical signals within the soma prior to the initiation of axonal action potentials. Thus, Nav1.1 may play a fundamental role in controlling electrical excitability. In the CNS, Nav1.1 was detected at high levels in the hippocampus, cerebellum, spinal cord, brainstem, cortex, substantia nigra, and caudate. Nav1.1 expression increases during the third postnatal week and peaks at the end of the first postnatal month. In contrast, Nav1.3 is expressed mostly during the embryonic period. Its expression disappears in most of the brain regions in rodent adults, and is much weaker than that of other sodium channels in human adults. Thus, Nav1.1 is the main sodium channel that is distributed and functioning over a large area in dendrites and soma in human being.