Action of sleeping drugs. Artwork of the face of a sleeping woman cut away to show a magnified image of sleeping drugs acting on nerve cells (neurones, upper left & right) in her brain. Two neurones meet at a gap called a synapse (centre). Sleeping drugs like benzodiazepines (yellow & green spheres) mimic the action of the neurotransmitter GABA (gamma-aminobutyric acid, red spheres). When GABA is released by a nerve cell it crosses the synapse and binds with receptors on the other nerve cell (not seen), resulting in the opening of chloride channels. Chloride ions then pass through, making the receptor nerve cell less excitable and aiding sleep.