Vomeronasal organ
From Freepedia
The vomeronasal organ (VNO) or Jacobson's organ (sometimes misspelled "Jacobsen's") is an auxiliary olfactory sense organ in some tetrapods. In adults, it is located in the vomer bone, between the nose and the mouth. It develops from the nasal (olfactory) placode, at the anterior edge of the neural plate.
Its function is somewhat mysterious. The sensory neurons within the vomeronasal organ detect distinct chemical compounds, often but not always large molecules. The vomeronasal organ is used in the detection of pheromones in some animals such as mice, although some pheromones are detected by the regular olfactory organ, and the vomeronasal organ detects other compounds in addition to pheromones. Cats sense nepetalactone from catnip using the vomeronasal organ.
Snakes use it to smell prey, sticking their tongue out and touching it to the opening to the organ. Some mammals use a distinctive facial movement called flehmen to direct compounds to this organ, while in some other mammals the entire organ contracts or pumps to draw in compounds.
Anatomical studies demonstrate that in humans the vomeronasal organ regresses during fetal development, as is the case with some other mammals, including cetaceans, some bats, and apes. There is no evidence of a neural connection between the organ and the brain in adult humans. Nevertheless, a small pit can be found in the nasal septum of some people, and some researchers have argued that this pit represents a functional vomeronasal organ. Thus, its possible presence in humans remains controversial.
