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From the Experts: The Primary Mechanism of Odor Perception

By: Mans Boelens, Boelens Aroma Chemical Information Service; and Harrie Boelens, Leiden University
Posted: October 18, 2005, from the November 2005 issue of P&F magazine.

In Ohloff et al.’s “Scent and Fragrances”, a chapter is devoted to the anatomy, physiology and biochemistry of scent receptors.1 This chapter gives an excellent review of the knowledge about the subject up to 1995.

The Regio olfactoria contains up to 50 million primary sensory cells (Nervus olfactorius), accompanied by a much larger number of supporting and basal cells, which are permanently regenerated with a half-life of about 10 days. These sensory cells, which are bipolar neurons, are in contact with the outer atmosphere through an extension that ends in a bundle of cilia (Cilia olfactoria), which are embedded in the mucus that coats the surface of the olfactory mucosa (F-1). The olfactory cells form axons that are bundled (Filia olfactoria) to tracers the cribiform plate of the ethmoid bone, reaching the olfactory bulb (Bulbus olfactorius) of the brain, where they converge with post-synaptic cells to form synaptic structures called glomeruli. The first synapses are on the dendrites of the mitral cells. These synapses transmit olfactory information into the olfactory bulb of the brain (Rhinencephalon) and into parts of the brain where higher level processing of odors takes place (olfactory divergence). In addition to the olfactory nerves, the olfactory mucosa contains the trigeminal nerve (Nervus trigeminus), whose impulses from odorants are not transmitted to the olfactory bulb but are processed independently.

Sensory stimulation is initiated when an odorant comes in contact with parts of the receptor membrane in the cilia.2 The static potential of a cell membrane is disrupted level centers of the central nervous system (CNS) and decoded into olfactory perceptions. The semantic description is the result of signal analysis and its comparison with a known odor pattern.

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