INFORMATION: SMELL/TASTE
http://www.brainfacts.org/sensing-thinking-behaving/senses-andperception/articles/2012/taste-and-smell/\
Taste and Smell
Although most of us don’t think of it in this way,
the related senses of taste and smell help us
interpret the chemical world.
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Taste and smell are separate senses with their own receptor organs, yet they are
intimately entwined. Tastants, chemicals in foods, are detected by taste buds, which
consist of special sensory cells. When stimulated, these cells send signals to specific areas
of the brain, which make us conscious of the perception of taste. Similarly, specialized
cells in the nose pick up odorants, airborne odor molecules. Odorants stimulate receptor
proteins found on hairlike cilia at the tips of the sensory cells, a process that initiates a
neural response. Ultimately, messages about taste and smell converge, allowing us to
detect the flavors of food.
Illustration by Lydia V. Kibiuk, Baltimore, MD; Devon Stuart, Harrisburg, PA
Just as sound is the perception of changes in air pressure and
sight the perception of light, tastes and smells are the perception
of chemicals in the air or in our food. Separate senses with their
own receptor organs, taste and smell are nonetheless intimately
entwined.
This close relationship is most apparent in how we perceive the
flavors of food. As anyone with a head cold can attest, food
“tastes” different when the sense of smell is impaired. Actually,
what is really being affected is the flavor of the food, or the
combination of taste and smell. That’s because only the taste, not
the food odors, are being detected. Taste itself is focused on
distinguishing chemicals that have a sweet, salty, sour, bitter, or
umami taste (umami is Japanese for “savory”). However,
interactions between the senses of taste and smell enhance our
perceptions of the foods we eat.
Tastants, chemicals in foods, are detected by taste buds, special
structures embedded within small protuberances on the tongue
called papillae. Other taste buds are found in the back of the
mouth and on the palate. Every person has between 5,000 and
10,000 taste buds. Each taste bud consists of 50 to 100
specialized sensory cells, which are stimulated by tastants such
as sugars, salts, or acids. When the sensory cells are stimulated,
they cause signals to be transferred to the ends of nerve fibers,
which send impulses along cranial nerves to taste regions in the
brainstem. From here, the impulses are relayed to the thalamus
and on to a specific area of the cerebral cortex, which makes us
conscious of the perception of taste.
Airborne odor molecules, called odorants, are detected by
specialized sensory neurons located in a small patch of mucus
membrane lining the roof of the nose. Axons of these sensory
cells pass through perforations in the overlying bone and enter
two elongated olfactory bulbs lying against the underside of the
frontal lobe of the brain.
Odorants stimulate receptor proteins found on hairlike cilia at
the tips of the sensory cells, a process that initiates a neural
response. An odorant acts on more than one receptor, but does
so to varying degrees. Similarly, a single receptor interacts with
more than one different odorant, though also to varying degrees.
Therefore, each odorant has its own pattern of activity, which is
set up in the sensory neurons. This pattern of activity is then sent
to the olfactory bulb, where other neurons are activated to form a
spatial map of the odor. Neural activity created by this
stimulation passes to the primary olfactory cortex at the back of
the underside, or orbital, part of the frontal lobe. Olfactory
information then passes to adjacent parts of the orbital cortex,
where the combination of odor and taste information helps
create the perception of flavor.
http://science.howstuffworks.com/life/human-biology/taste1.htm
Page 1 2 3 4
2007 HowStuffWorks
Sensation to Perception
Taste begins with sensation in the form of electrical impulses. Sensations,
however -- responses to stimuli like pressure, light or chemical composition
-- become perceptions like touch, vision or taste only when they reach the
brain.
Different stimuli activate different sensory receptors. Chemical stimuli
activate the chemoreceptors responsible for gustatory and olfactory
perceptions. Because taste and smell are both reactions to the chemical
makeup of solutions, the two senses are closely related. If you've ever had
a cold during Thanksgiving dinner, you know that all of the subtlety of taste
is lost without smell.
In some species, however, the two chemical senses are practically one.
Invertebrates like worms do not have distinctions between gustatory and
olfactory receptors. They instead differentiate between volatile and
nonvolatile chemicals.
In humans, the chemoreceptors that detect taste are called gustatory
receptor cells. About 50 receptor cells, plus basal and supporting cells,
make up one taste bud. Taste buds themselves are contained in gobletshaped papillae -- the small bumps that dot your tongue. Some papillae
help create friction between the tongue and food.
Every gustatory receptor cell has a spindly protrusion called a gustatory
hair. This taste hair reaches the outside environment through an opening
called a taste pore. Molecules mix with saliva, enter the taste pore and
interact with the gustatory hairs. This stimulates the sensation of taste.
Once a stimulus activates the gustatory impulse, receptor cells synapse
with neurons and pass on electrical impulses to the gustatory area of the
cerebral cortex. The brain interprets the sensations as taste.
In the next section, we'll learn about the primary tastes and how taste gives
us clues about what we eat.
http://en.wikipedia.org/wiki/Taste
Taste
From Wikipedia, the free encyclopedia
Jump to: navigation, search
This article is about the sense. For the social and aesthetic aspects of
"taste", see Taste (sociology). For other uses, see Taste (disambiguation).
Taste bud
Taste, gustatory perception, or gustation[1] is one of the five traditional
senses. Taste is the sensation produced when a substance in the mouth
reacts chemically with receptors of taste buds. Taste, along with smell
(olfaction) and trigeminal nerve stimulation (which also handles touch for
texture, also pain, and temperature), determines flavors, the sensory
impressions of food or other substances.
Humans perceive taste through sensory organs called taste buds,[2] or
gustatory calyculi, concentrated on the top of the tongue.[3] The tongue is
covered with thousands of small bumps called papillae, which are easily
visible to the naked eye. Within each papilla are hundreds of taste buds,
the organ of taste transduction.[4] There are between 2000 and 5000[5]
taste buds that are located on the back and front of the tongue. Others are
located on the roof, sides and back of the mouth, and in the throat. Each
taste bud contains 50 to 100 taste receptor cells. Taste perception fades
with age: On average, people lose half their taste receptors by time they
turn 20.[4]
The sensation of taste can be categorized into five basic tastes:
sweetness, sourness, saltiness, bitterness, and umami. Taste buds are
able to differentiate among different tastes through detecting interaction
with different molecules or ions. Sweet, umami, and bitter tastes are
triggered by the binding of molecules to G protein-coupled receptors on the
cell membranes of taste buds. Saltiness and sourness are perceived when
alkali metal or hydrogen ions enter taste buds, respectively.[6] As taste
senses both harmful and beneficial things, all basic tastes are classified as
either aversive or appetitive, depending upon the effect the things they
sense have on our bodies.[7] Sweetness helps to identify energy-rich
foods, while bitterness serves as a warning sign of poisons.[8]
The basic tastes contribute only partially to the sensation and flavor of food
in the mouth — other factors include smell,[2] detected by the olfactory
epithelium of the nose;[9] texture,[10] detected through a variety of
mechanoreceptors, muscle nerves, etc.;[11] temperature, detected by
thermoreceptors; and "coolness" (such as of menthol) and "hotness"
(pungency), through chemesthesis.
http://blog.odotech.com/bid/89722/On-the-way-to-understand-how-we-perceiveodors
We are honoured to present you a special blog edition written by our guest
author Dr. Johannes Frasnelli.
Dr. Frasnelli specialises in odor perception. He conducts research in the field
of neurophysiology of smell and taste as well as therapy in loss of the
chemical senses.
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When studying the sense of smell it is always a good idea to look at the other senses
as well. Many features in the individual senses have the same characteristics,
because evolution and biology is economic. So if we know something about seeing or
hearing, then there is a certain chance that the sense of smell works in a similar
fashion. And we do know a lot more about seeing or hearing than about smelling.
So, if one wants to know about how we perceive odors, it is a good idea to first look
how we perceive images or sounds. Here I am not talking about what happens in the
eyes, ears or in the nose, because that is pretty different for each individual sense.
What we are looking for now is how the brain treats the information from the
different senses. In order to understand how we analyse smell information, let’s first
look how we analyse visual or auditory information.
One of the main features, if not the most important feature of an image or a sound is
its intensity. So, a very weak visual stimulus will be perceived as pretty dark, a very
weak auditory stimulus will be perceived as very silent. On the other hand of the
scale, a very intense visual stimulus is perceived as very bright, and a very intense
sound is perceived as very loud. And this analogy is true for smell as well. A very
weak olfactory stimulus is perceived as a weak smell, and other hand, a very strong
stimulus is perceived as a very strong smell.
Source: Wikipedia
What is the basis of a strong or weak stimulus in the different sensory systems? If a
light source emits a lot of photons which then reach the retina, we perceive a strong
light. If a sound source emits very strong pressure waves which reach the ear drum,
we perceive a loud sound. The equivalent of the photons for seeing and the pressure
waves for hearing is, in the case of olfaction, the number of odor molecules, or in
other words, the concentration. Therefore, if an odor source emits a lot of
molecules, we perceive a strong odor. If an odor source emits only few odor
molecules, we perceive a weak odor. This is however only true for a given substance.
There is the possibility that for one substance we need many molecules to have a
very faint odor perception, and for another, a few molecules may be enough to
evoke a strong smell.
So, we have seen that the concept of intensity exists and is valid for the sense of
smell as it is for seeing and hearing.
But what about the next step, what about more complicated characteristics of the
stimulus. What are the next key characteristics in the other sensory systems? For
example, in vision, another key feature, next to intensity, is color. Let’s look at color:
different colors are evoked by different wavelengths (frequencies) of the
electromagnetic wave which reaches the eyes. Short frequencies evoke purple and
blue colors; long frequencies evoke red and yellow colors. Again, we have something
analogous in the auditory system: different wavelengths (frequencies) of the
pressure waves evoke sounds of a different pitch. Short wavelengths (frequencies)
evoke a sound with a high pitch; longer frequencies evoke sounds with a low pitch.
Unfortunately, the sense of smell is structured in a completely different way than
seeing and hearing. Smell perception is not based on perception of frequencies
(although some, but very few, researchers do think so). So, do the analogies
between seeing, hearing and smelling stop here?
Fortunately not. But we have to look at the brain from a different angle. We know
that those basic features, which are also called dimensions, in seeing and hearing are
encoded in brain structures. What does that mean? There are some cells in the area
of the brain processing input
from the eyes which react to only one color, let’s say
red, but not to another color, let’s say blue. Similarly, in the parts of the brain
processing auditory information there are some cells which react to high pitch
sounds exclusively, and some others which react to low pitch sounds exclusively. We
can therefore be positive that color and pitch are dimensions of vision and audition,
respectively, which are encoded in the brain.
Source: wikipedia
So, let’s look at the sense of smell. We know there is no equivalent of wavelength in
olfaction. If one would however be able to find cells, zones or regions in the brain
which react to one feature of smells, but not to the other, he could conclude that this
feature is a dimension
of smell, just as intensity is. The hunt for these features of
smells has started some years ago and is not yet over. Several concepts have been
put forward, and some of them fulfill the criteria above. We know now that, next to
the intensity of odors – which we know is caused by the concentration of the odorant
and which is therefore one dimension of odors – those dimensions may include the
chemical structure of the odorant, the pleasantness of the odor, and the edibility of
the odor source.
http://www.extension.iastate.edu/publications/pm1963a.pdf
The Science of Smell Part 1:
Odor perception and physiological
response
Olfaction, the sense of smell, is the least understood of the five senses. This, among other factors,
makes the task of reducing livestock odors a considerable challenge.
Odor terminology and perception
An odorant is a substance capable of eliciting an olfactory response whereas odor is the sensation
resulting from stimulation of the olfactory organs. Odors play an important part in our everyday
life, from appetite stimulation to serving as warning signals for disease detection. A number of
diseases have characteristic odors including gangrene, diabetes, leukemia, and schizophrenia.
Odors have been implicated in depression and nausea as well.
Detectable odors can have a significant impact
on people by affecting moods as well as having physiological impacts on the olfactory system.
People associate odors with past experiences and, from those experiences, involuntarily assess the
odor as likable, dislikable or indifferent. Effects on individuals, however, vary from one person to
another.
Odor threshold is a term used to identify the concentration at which animals respond 50 percent
of the time to repeated presentations of an odorant. This term is reserved, primarily, for use in
research with animals. Most often, however, odor threshold is used to mean detection threshold,
which identifies the concentration at which 50 percent of a human panel can identify the presence
of an odor or odorant without characterizing the stimulus. Detection threshold is the term most
frequently used when discussing odor research results associated with livestock operations. The
recognition threshold is the concentration at which 50 percent of the human panel can identify the
odorant or odor, such as the smell of ammonia or peppermint.
Although the detection threshold concentrations of substances that evoke a smell are slight (table
1), a concentration only 10 to 50 times above the detection threshold value often is the maximum
intensity that can be detected by humans. This, however, is in contrast to other sensory systems
where maximum intensities are many more multiples of threshold intensities.The maximum
intensity of sight, for instance, is about 500,000 times that of the threshold intensity and a factor
of 1 trillion is observed for hearing. For this reason, smell often identifies the presence or absence
of odor rather than quantifies its intensity or concentration.
The ability to perceive an odor varies widely among individuals. More than a thousandfold difference between the least and the most sensitive individuals in acuity have been observed.
Differences between individuals are, in part, attributable to age, smoking habits, gender, nasal
allergies, or head colds. Nonsmokers over the age of 15 show greater acuity than smokers in
general. Furthermore, females tend to have a keener
sense of smell than males, a finding that has
been substantiated in recent work at Iowa State University. Generally, the olfactory sensory
nerves atrophy from the time of birth to the extent that only 82 percent of the acuity remains at
the age of 20; 38 percent at the age of 60 and 28 percent at the age of 80. Consequently, olfactory
acuity and like or dislike of an odor decrease with age.
Infants appear to like all classes of odorous materials, perhaps because the lack previous
experience and because of their innate curiosity. Children younger than five years old rated sweat
and feces as pleasant but above that age, as unpleasant. Like and dislike of a particular odor can
change with odor concentration or intensity. Generally, humans can distinguish between more
PM 1963a May 2004