Biological Olfaction - The Electronic Nose Artificial Olfaction Technology - page 77

acts on the channel during the odor response and decrease its sensitivity to cAMP,
so requiring odor stimulus to produce sufficient cAMP to open the channel. As in
vertebrates, invertebrates have both excitatory and inhibitory responses to odors,
so there are likely to be multiple transduction pathways.
3.5 Encoding of Smell
The ability to measure things is a critical component in scientific inquiry. If you're
studying the strength of scents and their impact on people, you need to come up
with a standardized unit of what exactly constitutes the sensory input of smell. To
that end, Danish professor Dr. P. Ole Fanger created the smell measurement unit
known as an ''Olf'', short for ''olfaction unit'' derived from the Latin word
''olfactus'' which means smelled. 1 Olf is the strength of the smell produced by a
healthy adult working a sedentary job, in a climate controlled environment, with
the hygienic equivalent of 0.7 baths per day, and a skin surface area of 1.8 m 2 .
Using that as a base measure, the ''Olf'' factor of other things can be deter-
mined. A heavy smoker, for example, generates 25 Olfs. An athlete after partic-
ipation in a strenuous sport generates 30 Olfs. A non-porous and virtually scentless
material like polished Marble gives off a mere 0.01 Olfs per square meter of
surface area.
The olfactory receptor nerves located at the upper limit of the nasal cavity out
of the airflow channel. Together with mucous-secreting cells and basal cells, they
make up the odor detection apparatus. The receptor portions of the olfactory
neuron resemble cilia that extend to the mucosa surface. The finding sites on these
ciliated nerves await specific molecules that diffuse from the inspired airstream
under normal breathing. Direct transport of air is affected by sniffing that creates
turbulence and opens up passages by the turbinate's. Switching to oral breathing
can mitigate the intensity of malodorous compounds. When reaching the mucosa,
odorous molecules must be dissolved before binding to activate a neural impulse.
The impulse moves into the olfactory bulb in the brain, which is a complex neural
structure. This second-stage processed signal then travels to the limbic system and
the thalamus- cortex regions of the brain. The limbic cortex region affects
behavioral reactions associated with smell, whereas the thalamus-cortical region is
conscious interpretation of smell. Many of us share the experience of recalling a
memory when we encounter a particular odor.
Odor encoding is a spatially distributed process. Single odors can activate broad
overlapping regions, it is clear that individual neurons—and thus possibly the
receptor proteins themselves—can be activated by many odorants, including ones
that belong to different chemical families, underlying different odor qualities.
Because odorants are such complicated stimuli, we don't yet have a complete
picture of how smell is encoded by the brain. Different areas of the mucosa are
sensitive to different types of odorants. Smells appear to be organized spatially in
the olfactory bulb (similar smells are grouped together). An odotope is a group of