Odorant

An odorant is a volatile chemical compound capable of producing a smell by activating the olfactory system. In mammals, odorants are typically small, hydrophobic organic molecules that can evaporate at ambient temperatures and reach the olfactory epithelium in the nose via inhalation. They span a wide range of chemical classes, including terpenoids, aldehydes, ketones, esters, alcohols, sulfides, and nitrogen-containing compounds. Many odorants are chiral; enantiomers can be perceived with different smells or intensities.

Detection and neural coding: Odorants interact with olfactory receptor neurons, each of which expresses one type of odorant receptor gene, a G protein-coupled receptor. Binding of an odorant to its receptor initiates a signaling cascade via Golf, activating adenylyl cyclase and increasing cyclic AMP, which opens cAMP-gated ion channels and depolarizes the neuron. The axons of ORNs converge on glomeruli in the olfactory bulb, where signals are relayed to mitral and tufted cells and then to higher olfactory centers in the brain. The perception of a particular odor arises from a combinatorial pattern of receptor activations rather than a one-to-one mapping.

Other notes: Odorant transport in the nasal mucus is aided by odorant-binding proteins and other solubilizing factors. Odor perception can be influenced by concentration, background odorants, and prior experience, and mixtures can produce novel percepts.