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Vertebrate olfaction was first derived in an aquatic ecosystem, where water was the primary medium for odorants. Lancelets, a class of fish-like marine chordates, are the most distantly related ancestors that share the same olfactory receptors (OR) with humans. [3]
The olfactory receptor gene family in vertebrates has been shown to evolve through genomic events such as gene duplication and gene conversion. [37] Evidence of a role for tandem duplication is provided the fact that many olfactory receptor genes belonging to the same phylogenetic clade are located in the same gene cluster. [38]
The olfactory receptor proteins are members of a large family of G-protein-coupled receptors (GPCR) arising from single coding-exon genes. Olfactory receptors share a 7-transmembrane domain structure with many neurotransmitters and hormone receptors and are responsible for the recognition and G protein-mediated transduction of odorant signals. [5]
A modern demonstration of that theory was the cloning of olfactory receptor proteins by Linda B. Buck and Richard Axel (who were awarded the Nobel Prize in 2004), and subsequent pairing of odor molecules to specific receptor proteins. [9] Each odor receptor molecule recognizes only a particular molecular feature or class of odor molecules.
The olfactory bulb transmits smell information from the nose to the brain, and is thus necessary for a proper sense of smell. As a neural circuit, the glomerular layer receives direct input from afferent nerves, made up of the axons from approximately ten million olfactory receptor neurons in the olfactory mucosa, a region of the nasal cavity.
Olfactory receptor 3A2 is a protein that in humans is encoded by the OR3A2 gene. [ 5 ] [ 6 ] [ 7 ] Olfactory receptors interact with odorant molecules in the nose, to initiate a neuronal response that triggers the perception of a smell.
The surface of the cilia is covered with olfactory receptors, a type of G protein-coupled receptor. Each olfactory receptor cell expresses only one type of olfactory receptor (OR), but many separate olfactory receptor cells express ORs which bind the same set of odors. The axons of olfactory receptor cells which express the same OR converge to ...
Inside of these olfactory organs there are neurons called olfactory receptor neurons which, as the name implies, house receptors for scent molecules in their cell membrane. The majority of olfactory receptor neurons typically reside in the antenna. These neurons can be very abundant; for example, Drosophila flies have 2,600 olfactory sensory ...