Olfactory transduction

Olfactory transduction is a series of events in which odor molecules are detected by olfactory receptors and chemical signals are transformed into electrical signal to the brain where they are perceived as smells.

Once ligands (odorant particles) bind to specific receptors on the external surface of cilia, olfactory transduction is initiated. In mammals, olfactory receptors have been shown to signal via G protein. This is a similar type of signaling of other known G protein-coupled receptors (GPCR). The binding of an odorant particle on an olfactory receptor activates a particular G protein (Gαolf), which then activates adenylate cyclase, leading to cAMP production. cAMP then binds and opens Cyclic nucleotide-gated ion channel. This opening allows for an influx of both Na+ and Ca2+ ions into the cell, thus depolarizing it. The Ca2+ in turn activates chloride channels, causing efflux of Cl-, which results in a further depolarization of the cell.

The odorant-activated cAMP cascade in the olfactory sensory neuron is subject to negative feedback regulation, like all other G-protein mediated pathways. This contributes to response deactivation and adaptation to stimulus.

Individual odorants activate subsets of receptors. Receptors also have varying affinities for odorant molecules. In addition, higher concentrations of odorants elicit activity from greater a number of receptors than do lower concentrations. Thus, odor intensity as well as odor identity is represented by combination of a number of activated receptors.