Ligand-gated ion channels (LGIC) comprise several families of related membrane receptors that function as transducers of neurotransmitter signals. This review focuses on the structural and functional relationship between the nicotinic acetylcholine receptor (AChR) protein and its membrane microenvironment and on the specific nongenomic modulation exerted by sterols in general, and steroids in particular. Differences in the inhibitory potency of a particular steroid in muscle and neuronal types of AChR, archetypal members of the LGIC superfamily, and in different subtypes of neuronal AChRs are discussed. The structural basis for steroid action is analyzed using functional studies at the single-channel level in correlation with site-directed mutagenesis and in vitro studies using fluorescence spectroscopy. The combination of these approaches provides an initial scaffold for unravelling the chemical basis of nongenomic, rapid effects of steroids on neurotransmitter receptors.