Voltage-gated Na^{­­­­­­­+} (Na_V) channels are important for the generation and propagation of signals in electrically excitable tissues like the muscle, heart, and nerve. Activation of these channels ultimately leads to muscular contraction, cardiac rhythm, and neuronal firing. Nine mammalian isoforms of voltage-gated Na­­­­­­­⁺ channels have been identified (Na_V1.1-Na_V1.9). Nine genes (SCN1A, SCN2A, etc.) encoding distinct α subunit isoforms and 4 β subunit genes (SCN1B, SCN2B, etc.) have been identified in the human genome. The nine isoforms share a similar (but complex) architecture.