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Olfactory Systems

The Olfactory Mucosa

The olfactory mucosa within the nasal cavity have receptor neurons which send information to the main olfactory bulbs via bundles of olfactory axons. The VNO receptor neurons have axons that leave the VNO capsule in bundles and extend dorsally across the nasal septum passing beneath the olfactory mucosa.

 

The Main Olfactory Bulbs

The main olfactory bulbs (MOBs) receive their information from bundles of olfactory axons which come from olfactory receptor neurons in the olfactory mucosa within the nasal cavity. The VNO information from the AOB and the olfactory information from the MOB are carried by separate sets of "second-order" axons to the amygdala.

 

The Accessory Olfactory Bulbs

The accessory olfactory bulbs (AOBs), to which VN nerves normally project in mammals, have not been clearly identified in humans, raising additional questions about human VNO function. The central target of VNO input in mammals, the amygdala, is present in humans and does receive chemosensory input. It probably shares some functions with the amygdala in other mammals but whether these include the analysis of purely vomeronasal input is not yet clear.

The Vomeronasal Organ

The vomeronasal organ (VNO), also known as the Jacobson's organ, is a chemoreceptor organ present in most tetrapod species. It is important in intraspecific chemical (pheromone) communication. The paired organs are separate from the main olfactory organ. In most species they are largely enclosed within a capsule formed by the vomer-bone or vomer-cartilage and are found within a bulge along each side of the base of the nasal septum.