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The main olfactory sense is derived from the more ancient neural system, broadly present across insects and mammals. [23] This system is specialized to detect volatile, airborne molecules. The accessory olfactory system is the more recently evolved structure, first appearing in the common ancestor of modern amniotes and amphibians.
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 sensory receptors of the accessory olfactory system are located in the vomeronasal organ. As in the main olfactory system, the axons of these sensory neurons project from the vomeronasal organ to the accessory olfactory bulb, which in the mouse is located on the dorsal-posterior portion of the main olfactory bulb.
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]
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.
The olfactory system, is the sensory system used for the sense of smell (olfaction). Olfaction is one of the special senses directly associated with specific organs. Most mammals and reptiles have a main olfactory system and an accessory olfactory system.
The axons of OSNs expressing the same odorant receptors converge onto the same glomerulus at the olfactory bulb, allowing for the organization of olfactory information. An olfactory receptor neuron (ORN), also called an olfactory sensory neuron (OSN), is a sensory neuron within the olfactory system .
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 ...