Toward Sensor to Reproduce Human Sense - The Electronic Nose Artificial Olfaction Technology - page 128

Similarly, a receptor interacts with many different odorants to varying degrees.
Schematic representation of odorant path in olfactory system is shown in Fig. 5.6 .
Odorant molecules have no obvious connections with each other except that
they are odorous, that is, they are inducing sensations in the olfactory system.
Olfactory system unique characteristic is that there is no limit to the number of
odorous molecules that can be detected and described. Odorous molecules are
mainly limited to molecules of 200-400 mW but within that range there
are essentially an infinite number of odorous molecules. The molecular structures
are highly variable and no individual or group of individuals has been exposed to
all of the range, or possibly even the majority of the range. The immune system
evolve to detect and respond to an open ended set of stimuli and has solved it by
using a variable rearrangement of its genetic code to generate protein receptors of
huge range. The olfactory system has solved this problem by generating a huge
number of individual receptor genes. The olfactory system requires one thirtieth of
the genome. An intriguing aspect of the olfactory system is that these odorant
receptor genes are involved both in odorant detection as well as establishing the
basic anatomy of the olfactory system that allows that detection [ 16 ].
Our ability to recognize, identifies, and discriminate an olfactory object across
contexts and against the background of other odors can be accomplished for simple
molecular compounds and not merely complex ecological odors. Though we
discussed in a general way ( Chap. 3 : Transduction mechanism) that the firing of
olfactory nerve fibers is the outcome of a non-specific increase in ionic perme-
ability, mediated by cAMP, how odorant molecules actually trigger this change
remains something of a uncertainty. Most probably there are receptor sites that
recognize particular molecules or classes of molecule, but the basis of this rec-
ognition it not as straight-forward a matter as one might imagine.
The neural systems for taste and smell are distinct from one another, the
feelings of flavors and aromas mostly work together, mainly during eating. Much
of what normally described as flavor comes from food molecules arrived up noses.
Additionally, these two senses both have connections to brain areas that control
emotions, regulate food and water intake, and form certain types of memories.
Connection between olfactory and gustatory systems is the constant proceeds of

Fig. 5.6 Odorant pathways