SCENT & SMELL OUR WAY
fit into the scent receptors the same way that a key fits into a lock.
And the flavor of food is a combined response to two of the
chemical senses; taste and odor. The
sense of odor is more sensitive even in human beings that the sense of
taste. The sense of odor is
the major contributor to the perception of flavor.
molecule has an odor is dependent on if it can excite and stimulate the
olfactory nerve endings inside the nose.
In humans, these nerve endings occupy an area of yellow-brown
colored epithelium that is about 5 sq. cm. (square centimeters or 1 inch
X 1 inch). It is in wafting
a scent utilizing eddy
currents that this area is able to perceive odor.
When one sniffs and sniffs, it is the eddy currents, not direct
blasts, that carry the molecules to this area."
is the rule of the aromatherapy enthusiast.
Sense of Smell is an interesting phenomenon.
There are 50 million or so receptors that compose the olfactory
epithelium and these are all bare nerve endings.
There is no buffer between the outside world and these bare nerve
receptor of the olfactory epithelium.
Thus the nervous system is in direct contact with the outside
world: the brain is exposed in the nose.
This part of the brain, the smell brain or reptilian brain with
its exposed sense of smell suggests that it is the oldest and most
primitive of the senses. We
smell therefore we are. Smell
is linked in terms of physical closeness with one of the more
primitive parts of the brain, the limbic
system which is the seat of memory and learning, the place and home
and seat of the control of emotions.
We can perceive odors therefore we are alive and in direct
contact with that which has made the human race human. This limbic
system is the seat of the control of emotions and this may be the reason
that scent can have such a powerful impact on our psyche.
molecules are called odor vectors or osmophores (smell carrier).
(Osmo = smell in Greek and phore = to bear or to be borne).
It is unknown what the relationship is between the molecular
structure of the molecules and the sensation they create that we call
odor vector must be volatile
to reach the nose and secondly, it must be slightly soluble in water in
order to dissolve in the mucus. It
is possible that these molecules act as detergents in order to carry
insoluble molecules into the receptor sites.
It must interact with a protein molecule in the olfactory nerve
endings, be able to modify its shape, and thus stimulate the nerve cell
to send a smell (or other) message to the brain.
is probable that the same lock-and-key mechanism of taste operates the
sense of smell. A molecule
of a particular shape can attach to a given protein molecule so long as
it matches its shape in some respect.
30 types of anosmia exist, which suggests at least 30 different types of
locks that can be opened with the correct key (molecule).
Only a part of a molecule needs to fit snugly into a site to
trigger a scent signal. If
it is flexible it can fit into more than one site and excite a mixed
in the olfactory epithelium, among the mucus-exuding cells, are cells
that are part of the system that innervates the face (trigeminal nerve).
It is suspected that pungent and putrid molecules penetrate them,
interact with their proteins, and stimulate them to fire.
Thus, there are two types of olfaction: first
smell, the ordinary type for specific odors, and second smell for nonspecific pungency and putridity."
color of the smell
area is important as well. "Found at the upper end of each
nostril, the olfactory regions are yellow, richly moist, and full of
fatty substances. We think
of heredity as ordaining (such physical characteristics as) how tall one
will be, the shape of the face, and the color of the hair. Heredity also
determines the shade of yellow of the olfactory area.
The deeper the shade, the keener and more acute the sense of
smell. Albinos have a poor
sense of smell. Animals,
which can smell the beatific grandeur, have dark-yellow olfactory
regions; ours (humans) are light yellow. The fox is reddish brown, the
cat's an intense mustard brown."
Thus these animals have a more pronounced ability to detect
P.W. Atkins: MOLECULES;
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