page_title: Vomeronasal organ
section_title: Animals which possess
hierarchical_section_title: Vomeronasal organ / Animals which possess
context_page_description: The vomeronasal organ, or Jacobson's organ, is the paired auxiliary olfactory sense organ located in the soft tissue of the nasal septum, in the nasal cavity just above the roof of the mouth. The name is derived from the fact that it lies adjacent to the unpaired vomer bone in the nasal septum. It is present and functional in all snakes and lizards, and in many mammals, including cats, dogs, horses, cattle, pigs, and some primates; in humans it is present, but is vestigial and non-functional.
  The VNO contains the cell bodies of sensory neurons which have receptors that detect specific non-volatile organic compounds which are conveyed to them from the environment. These compounds emanate from prey, predators, and the compounds called sex pheromones from potential mates. Activation of the VNO triggers an appropriate behavioral response to the presence of one of these three.
  VNO neurons are activated by the binding of certain chemicals to their G protein-coupled receptors: they express receptors from three families, called V1R, V2R, and FPR.
context_section_description: The functional vomeronasal system is found in all snakes and lizards, and many mammals.
  Salamanders perform a nose-tapping behavior to presumably activate their VNO.
  Snakes use this organ to sense prey, sticking their tongue out to gather scents and touching it to the opening of the organ when the tongue is retracted.
  The organ is well developed in strepsirrhine primates such as lemurs and lorises, developed to varying degrees in New World monkeys, and underdeveloped in Old World monkeys and apes.
  Elephants transfer chemosensory stimuli to the vomeronasal opening in the roof of their mouths using the prehensile structure, sometimes called a finger, at the tips of their trunks.
  Painted turtles use this organ to use their sense of smell underwater.
  Garter snakes – In addition to the main olfactory system, garter snakes also have the vomeronasal system which consists of the vomeronasal organ. The vomeronasal organ plays an important role in some vertebrates with its sensitivity toward chemicals that are related to mating or sensing prey. For example, the snakes use the organ to detect the presence of prey or predator by gathering the chemical cues in the environment through the flicking behavior of the forked tongue. Moreover, garter snakes also uses the vomeronasal organ in their pheromone communication as well. Particularly, there should be a distinction made between the odors and vomodors. Odors are chemicals detected by the sensory cells in the nasal epithelium through the process of olfaction. Vomodors are chemicals detected by the sensory cells from the vomeronasal organ through the process of vomerolfaction.  Upon entering the lumen of the organ, the chemical molecules will come into contact with the sensory cells which are attached to the neurosensory epithelium of the vomeronasal organ.  More importantly, a new research has demonstrated that the vomeronasal organ is necessary in order for garter snake to respond to airborne prey odors, but fail to respond to airborne nonprey odors.
  In some other mammals the entire organ contracts or pumps in order to draw in the scents.
caption: Sagittal section of the vomeronasal organ of garter snake
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