Tetrodotoxin (TTX) is a potent neurotoxin that acts by binding to voltage-gated sodium channels in excitable cells, blocking the flow of sodium ions and preventing the generation of action potentials. The structure of TTX is characterized by a unique fused tricyclic ring system fused with an eight-membered ring known as the tetrodotoxin ring. This ring structure is highly rigid and contains several nitrogen atoms involved in hydrogen bonding and cation binding. The overall structure of TTX can be described as a complex array of fused rings with multiple functional groups, including hydroxyl, amine, and guanidine moieties, which contribute to its biological activity.