The anterior olfactory nucleus (AON) also called the anterior olfactory cortex, is a major early processing area for

olfaction The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste. In humans, ...

located behind the

olfactory bulb The olfactory bulb (Latin: ''bulbus olfactorius'') is a neural structure of the vertebrate forebrain involved in olfaction, the sense of smell. It sends olfactory information to be further processed in the amygdala, the orbitofrontal cortex (OF ...

, and in the olfactory tract (olfactory peduncle). The AON connects the olfactory processing centres of both hemispheres. It is involved in the

sense of smell The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste. In humans, it ...

(olfaction), and has influence on other olfactory areas including the olfactory bulb and the piriform cortex. The AON is one of the major secondary structures of olfaction.

Structure

The AON is found behind the

and in front of the piriform cortex (laterally) and olfactory tubercle (medially) in the olfactory tract (also olfactory peduncle) or retrobulbar area. The peduncle contains the AON as well as two other much smaller regions, the ventral and dorsal tenia tecta.

Function

The AON plays a pivotal but relatively poorly understood role in the processing of odor information. Odors enter the nose (or olfactory rosette in fishes) and interact with the cilia of

olfactory receptor neuron An olfactory receptor neuron (ORN), also called an olfactory sensory neuron (OSN), is a sensory neuron within the olfactory system. Structure Humans have between 10 and 20 million olfactory receptor neurons (ORNs). In vertebrates, ORNs are Bi ...

s. The information is sent via the

olfactory nerve The olfactory nerve, also known as the first cranial nerve, cranial nerve I, or simply CN I, is a cranial nerve that contains sensory nerve fibers relating to the sense of smell. The afferent nerve fibers of the olfactory receptor neurons t ...

(CNI) to the olfactory bulb. After processing in the bulb the signal is transmitted caudally via the axons of

mitral cell Mitral cells are neurons that are part of the olfactory system. They are located in the olfactory bulb in the mammalian central nervous system. They receive information from the axons of olfactory receptor neurons, forming synapses in neuropils ...

s, and tufted cells in the lateral olfactory tract. The tract forms on the ventrolateral surface of the brain and passes through the AON, continuing on to run the length of the piriform cortex, while synapsing in both regions. The AON distributes the information to the contralateral olfactory bulb and piriform cortex as well as engaging in reciprocal interactions with the ipsilateral bulb and cortex. Therefore, the AON is positioned to regulate information flow between nearly every region where odor information processing occurs.

Components

The AON is composed of two separate structures: * a) a thin ring of cells encircling the rostral end of the olfactory peduncle known as “pars externa”, * b) the large “pars principalis”, seen in coronal sections of most mammalian brains as a two-layered structure. ** The deepest (Layer II) is a thick ring of pyramidal and other-shaped cells surrounding the anterior limb of the anterior commissure. ** The outer, cell-poor layer, is often subdivided into a superficial zone (Layer Ia, which contains the output axons from the olfactory bulb) and a deeper area (Layer Ib). ** Many divide pars principalis on the basis of the ‘compass points,’ yielding pars dorsalis, pars ventralis, pars medialis, pars lateralis, and pars posterioralis (often combined with pars ventralis to form “pars ventroposterioralis”).

References

External links

*
NIF Search - Anterior Olfactory Nucleus
via the

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