The primary events in chemical sensory perception: Olfaction as a model for selective chemical sensing

Early theories of olfaction are summarized after brief introductions to the anatomy of the human olfactory system and direct electrical measurements on receptor cells (electro-olfactography). The problems of odourant convection-diffusion, and transduction are discussed in terms of the physical chemistry of interfacial partitioning and membrane-receptor behaviour, respectively. Speculation is presented regarding the significant features of receptor structure required for analytical selectivity. Stimulant—receptor interaction at the membrane surface can lead to changes in membrane permeability to ions in a number of distinct ways. Current knowledge regarding the structure and membrane electrochemistry of the important neurotransmitter receptor for acetylcholine, is examined as a role model for the biological activity of olfactory receptors. Finally the olfactory system is compared concisely to existing chemical sensor technology. Although parallels exist, significant differences are obvious; an example is the particular chemistry exhibited by molecular receptors and the hybrid of digital and analogue coding for transduction.