Scent & Smell
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Smell -- one of the five senses --
is the sense
that allows us, with the help of organs in our nose and a process of memory and
associations in our brain, to recognize our world and to understand and adapt to
our environment.
It tells us what we like and dislike;
it tells us
with whom to fall in love.
It stimulates our appetite and enriches our eating
experience.
It triggers memories and affects our moods. The lack of it might
endanger our lives or leave us in state of depression.
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Smell is, on one hand, common to everyone and, at the
same time, very personal.
While one person might like one smell
another might despise it. This is because even though the trigger to each unique
scent originates from specific molecules that reach the nose – our experience
of smell is located in our brain.
When we breathe in, the air flows through
our nostrils, enters the nasal passages and is passed into our nasal cavity. The
air then moves down the back of our throat through the trachea (in other words,
through our windpipe) on its way to the lungs.
Inside the nose we have hair, some of
which is microscopic in size (called cilia), and a thin layer of tissue that is
actually a membrane that generates mucus.
This membrane helps to moisten the
air, to warm it and to catch germs, dust and other small particles that could
otherwise end in our lungs. The role of the cilia is to move the mucus out of
the sinuses and “brush it out”, to the back
of the nose.
On the top of the nasal cavity is the
olfactory epithelium. In human beings it contains more than 10 million
small receptors that are sensitive to odor molecules that float in the
air.
There are hundreds of different types of
odor receptors, each with the ability to sense certain odor molecules. Odor
molecules can stimulate several different kinds of receptors.
Illustrations
by Elad Tzadok, www.frozenjelly.com
When the smell receptors are stimulated,
signals travel along the olfactory nerve to the olfactory bulb which is situated
just above the nasal cavity and beneath the brain. Signals are sent from the
olfactory bulb directly to the brain to be interpreted as a smell.
The variation and combination of
stimulated receptors trigger different signals that are interpreted in our
brain, thus allowing our brain to recognize some 10,000 different smells. Compared to other animals this is
quite low.
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Dogs, for example, have about 200 million olfactory
receptors. They are able to sniff a trail of
a person days after they leave. This makes them more sensitive to smell
particles in the air than humans.
This is why dogs are used as odor
detectors by officials around the world in the war against crime and
terror.
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There is no absolute or objective
analytical way to measure odor scientifically since each person’s brain gets
slightly different signals and reacts differently to them due to different
experiences and memories.
Because of the complexity of the system
of triggers, there are currently only theories as to how the olfactory receptors
actually work:
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Vibration Theory:
The receptors react and detect the unique frequency and vibration within the
molecule which triggers the electric pulse to the brain.
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Shape Theory:
The scent molecules lock into olfactory receptors, based on their shape
alone. This theory suggests that there is a unique relation between a type
of receptor, a type of molecule shape and a specific smell. Each receptor
releases an electrical pulse to the brain, which in turn triggers a specific
emotional sensation (a specific scent).
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Odotope Theory: This
is an elaboration of the shape theory which argues that smell is the result
of a combination of receptors. In this theory receptors provide small bits
of information to the brain which pieces these bits of information together
like a puzzle to create an overall sensation of smell.
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Currently it is believed that an average
human can distinguish between an astonishing 10,000 distinct scents. Yet those
same 10,000 fragrances cause completely different experiences and reactions from
person to person, and can be different for the same person based on that
person’s emotional level.
Our olfactory receptors that send
electrical signals to the brain are connected to the limbic system, the most
primordial and primitive part of the brain, which is associated with emotions
and memory, linking our experience and overall sensation of a smell to our most
basic personal emotional core. |
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Studies tend to show a connection between exposure to
pleasant fragrances and positive emotional change. For instance, a person
who is exposed to a pleasant fragrance will have an elevated mood, as
opposed to those who were exposed to a placebo.
In addition it is more likely that people who are exposed to pleasant
scents will be deemed attractive by other people than people exposed to
scents that were considered to be unpleasant. This is a result of the
affect that the scent had on the person’s mood rather than the affect on
the people surrounding that person.
Some psychology experiments have even suggested that the real value of
perfume might be to affect the mood of the wearer rather than the
attraction it has for the opposite sex. |
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The term pheromone is derived from the
Greek word “pherein” (to transport) and the word “hormon” (to
stimulate).
Hormones are molecules that are created
by the endocrine system. They transport signals inside an organism, serving like
messengers that send orders for the biological activity of the body.
Pheromones are molecule scents created
by various organs of the body and are secreted from it through the secretory
organs. They float in the air and are used by animals and other life forms, with
the aid of the olfactory system, to communicate mostly within their own species.
Pheromones can be classified into a few
categories by the function they serve. A rough division will leave us with three
groups:
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Pheromones
that carry with them
a distinct olfactory stamp of an individual or a group,
thus enabling
them to be recognized or identified by others.
It is owing to this type of pheromones that a mother recognizes her
baby (and the baby recognizes its mother) a few hours after birth, the
buffalo recognizes it’s new born among thousands, the ants identify
their trail and the dogs and other animals define their territory.
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Alert Pheromones
– these are
generated by creatures or even plants in a case of danger.
These pheromones can also be recognized by different species thus
allowing them to respond by confronting the danger or by escaping from
it.
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The sex pheromones are the scent molecules that creatures release in
order to attract the opposite sex. In some instances, like in the
Lepidoptera (moth and butterfly families), the female sex hormone can
be detected by the males from a distance of up to 10 km.
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Sex Pheromones – These pheromones play a main role in the
synchronization of the fecundation and ovulation in sea life and also
in mammals. At the time
of ovulation, the female creates pheromones that trigger the male
passion for sexual behavior. This can be seen with horses, dogs,
monkeys and many other animals.
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Do humans have such pheromones and do we react to them?
There is some dispute about this.
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It is a known fact that each of us emits our own unique
smell (unless we have an identical twin) and in most cases we don’t even
notice it since we become accustomed to it.
In fact our body smell reflects our physiological state
and inner metabolism, our diet, our gender, reproductive phase, and our
health. In some cases certain types of diseases can make us produce smells
characteristic of that disease. For example, people with liver disease can
have a fishy smell on their breath.
Even though most humans usually don’t notice, scents can
affect our mood and in turn affect the smells we release. Yet
compared to some animals our detection levels are substantially low. |
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Research has shown that the sense of olfaction is stronger
in women than in men.
It reaches its peak around the time of ovulation and at
this time it is significantly stronger than during other phases of the
menstrual cycle.
There is a gene family (called the Major Histocompatibility Complex – MHC) which is found in most vertebrates that plays an important
role in the immune system and in the selection of mates. This group of
genes generates molecules that can be detected by the sense of
smell.
Research has indicated that we tend to select mates with different MHC
genes, thereby ensuring a healthier breeding pattern. |
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Although pheromones were discovered in the 1950s, the use
of them in perfume goes back to ancient periods. Natural pheromones, which are
produced by a few animals and by bees, were used as a base that was mixed with
jasmine, vanilla and other perfume plants.
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propolis and pheromone molecules that were generated by the bees.
Wax from different bee hives smells differently depending
on its location and the group of bees that produced it. The essence of the
wax is extracted by the aid of alcohol.
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Ambergris is a pheromone produced by the sperm whale which
is a marine mammal of the whale family. It was hunted, among other things, for
its ambergris, although there was no need for it since this substance grows
like a football in its stomach and is naturally regurgitated from it. The
ambergris floats in the ocean and can reach the shores of Somalia, Mauritania
and India where it can be collected. This pheromone has a sweet earthy odor and
was used, historically, in the production of perfume.
Pheromones from civet, wild beaver, hyrax and a few other
animals also were extracted for the production of perfume.
Today, the very high price and scarcity of these scents
make their use in mass production of perfume nearly impossible. Technology has
brought with it the development of synthetic substitutes. They are cheap,
readily available and while commonly used they are a poor imitation of the
original animal pheromones.
Read
more about the basic components of perfume...
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