5-HT3 differ from all other 5-HT (serotonin) receptors whose actions are mediated via G proteins. Their structure and function has placed them in the Cys-loop family of cationic ligand-gated ion channels. 5-HT3 receptors are located in both the peripheral (PNS) and central (CNS) nervous systems. In the CNS, 5-HT3 receptors may play roles in a variety of functions including emesis, cognition and anxiety, whereas in the PNS they play a role in a variety of sympathetic, parasympathetic and sensory functions (e.g. signaling in gastrointestinal tract, gut motility and peristalsis).