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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 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 main olfactory system detects airborne substances, while the accessory system senses fluid-phase stimuli. The senses of smell and taste (gustatory system) are often referred to together as the chemosensory system, because they both give the brain information about the chemical composition of objects through a process called transduction.
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 ...
Each receptor type is expressed within a subset of neurons, from which they directly connect to the olfactory bulb in the brain. [1] Olfaction is essential for survival in most vertebrates ; however, the degree to which an animal depends on smell is highly varied. [ 2 ]
In the olfactory bulb, the ORNs synapse with termination in the glomeruli. [6] Each glomerulus receives input from olfactory receptor neurons expressing only one type of olfactory receptor. The glomerular activation patterns within the olfactory bulb are thought to represent the quality of the odor being detected.
In animal anatomy, the rhinencephalon (from the Greek, ῥίς, rhis = "nose", and ἐγκέφαλος, enkephalos = "brain"), also called the smell-brain or olfactory brain, is a part of the brain involved with smell (i.e. olfaction). It forms the paleocortex and is rudimentary in the human brain. [citation needed]