Barbiturates are drugs that depress the central nervous system and are often called sleeping pills.
Barbiturates increase the flow of chloride ions across the neuronal membrane causing hyperpolarization (a more negative resting membrane potential). This occurs by binding the ionotropic receptor for the endogenous neurotransmitter known as gamma-amino-butyric-acid or GABA (Principally the GABAa isoform of the receptor). The increased chloride ion flow reduces the chance that an excitatory action potential will be generated. This is the way in which barbiturates act as depressants of the central nervous system and are effective sedatives, anxiolytics, and anticonvulsants.