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The vomeronasal organ (VNO), or the Jacobson's organ, is an auxiliary olfactory sense organ that is found in many animals. It lies close to the vomer and nasal bones. It was discovered by Frederik Ruysch prior to 1732 and later by Ludwig Jacobson in 1813.〔Jacobson, L. (1813). Anatomisk Beskrivelse over et nyt Organ i Huusdyrenes Næse. Veterinær=Selskapets Skrifter (Danish ) 2,209–246.〕 This organ is the sense organ involved in the flehmen response in mammals. The VNO is the first stage of the accessory olfactory system and contains sensory neurons that detect chemical stimuli. The axons from these neurons project to the accessory olfactory bulb, which targets the amygdala and bed nucleus of the stria terminalis, which in turn project to the hypothalamus. The vomeronasal organ is mainly used to detect pheromones, chemical messengers that carry information between individuals of the same species. As with other olfactory systems, chemical messages are detected by their binding to G protein-coupled receptors. The neurons in the VNO express receptors from three families, called V1R,〔Dulac C, Axel R. A novel family of genes encoding putative pheromone receptors in mammals. Cell. 1995 Oct 20;83(2):195-206.〕 V2R,〔Herrada G, Dulac C. A novel family of putative pheromone receptors in mammals with a topographically organized and sexually dimorphic distribution. Cell. 1997 Aug 22;90(4):763-73.〕〔Matsunami H, Buck LB. A multigene family encoding a diverse array of putative pheromone receptors in mammals. Cell. 1997 Aug 22;90(4):775-84.〕〔A new multigene family of putative pheromone receptors. Ryba NJ, Tirindelli R. ''Neuron''. 1997 Aug;19(2):371-9.〕 and FPR.〔Rivière S, Challet L, Fluegge D, Spehr M, Rodriguez I. Formyl peptide receptor-like proteins are a novel family of vomeronasal chemosensors. Nature. 2009 May 28;459(7246):574-7.〕〔Liberles SD, Horowitz LF, Kuang D, Contos JJ, Wilson KL, Siltberg-Liberles J, Liberles DA, Buck LB. Formyl peptide receptors are candidate chemosensory receptors in the vomeronasal organ. Proc Natl Acad Sci U S A. 2009 Jun 16;106(24):9842-7.〕 The receptors are distinct from each other and from the large family of receptors in the main olfactory system. Stimuli reach the VNO in liquid phase via a pumping mechanism; the primary cues for the VNO are therefore non-volatile and require direct physical contact. Its presence in many animals has been widely studied and the importance of the vomeronasal system to the role of reproduction and social behavior (through influence on anterior hypothalamus) has been shown in many studies. Its presence and functionality in humans was controversial, though most studies agree the organ regresses during fetal development. Many genes essential for VNO function in animals (such as TRPC2) are non-functional in humans. Chemical communication does appear to occur among humans, but this does not necessarily imply that the human vomeronasal organ is functional. ==Structure== The VNO is found at the base of the nasal cavity. It is split into two, being divided by the nasal septum, with both sides possessing an elongated C-shaped, or crescent, lumen. It is encompassed inside a bony or cartilaginous capsule which opens into the base of the nasal cavity.〔http://www.neuro.fsu.edu/~mmered/vomer/〕 The vomeronasal receptor neurons possess axons which travel from the VNO to the accessory olfactory bulb (AOB) or, as it's also known, the vomeronasal bulb. These sensory receptors are located on the medial concave surface of the crescent lumen. The lateral, convex surface of the lumen is covered with non-sensory ciliated cells, where the basal cells are also found. At the dorsal and ventral aspect of the lumen are vomeronasal glands, which fill the vomeronasal lumen with fluid. Sitting next to the lumen are blood vessels that dilate or constrict, forming a vascular pump that deliver stimuli to the lumen. A thin duct, which opens onto the floor of the nasal cavity inside the nostril, is the only way of access for stimulus chemicals. During embryological development, the vomeronasal sensory neurons form from the nasal (olfactory) placode, at the anterior edge of the neural plate (cranial nerve zero). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「vomeronasal organ」の詳細全文を読む スポンサード リンク
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