Transcript Smell and Taste

Why do we study taste and smell
together?
SENSORY INTERACTION: the principle that one
sense may influence another.
The senses of taste and smell have a very
cooperative working relationship.
Many of the subtle distinctions you may
think of as flavors really come from odors
 Often, if you can’t smell the food, you can’t
taste the food.
Five Distinct Tastes:
Five Distinct Tastes:

Each of these tastes developed as survival
functions, according to evolutionary
psychology.
Sweet - energy source
Sour – potentially toxic acid
Bitter – potential poisons
Salty – sodium essential to physiological
processes
Umami – proteins to grow and repair tissue
=the taste of glutamate (MSG) – savory taste
in meat and cheese
A Theory Debunked
Since 1942, tongue maps like this one were
widely published and touted as an accurate
portrayal of where certain taste receptors
were located.
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Wine glasses are even designed around this idea.
The notion that the tongue is mapped into
four areas—sweet, sour, salty and bitter—is
wrong. There are five basic tastes
identified so far, and the entire tongue
can sense all of these tastes more or less
equally.
The tongue map is easy enough to prove
wrong at home.
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Place salt on the tip of your tongue. You'll
taste salt.
For reasons unknown, scientists never
bothered to dispute this inconvenient
truth until 1974, and even today, many
textbooks still publish pictures of the
tongue map.
Remarkably, more is known about vision
and hearing, far more complicated senses,
than taste.
Gustatory system
Although we speak about taste it is always a combination of
odors (~ 75%) and tastes (~25%)
4 types of papillae on the surface of the tongue:
1. pp. filliformes (vlaknate), they do not contain taste buds, so
they are not a part of the gustatory system
2. pp. circumvallatae (opkopane), 10-12, “V” shape
3. pp. fungiformes (gljivaste, mushroom-like), mostly on the top
and on the lateral edges
4. pp. foliate (listaste), mostly in the posterior part
Papillae
Those bumps on our tongue
are called papillae.
Papillae help grip food while
your teeth are chewing. They
also have another special job

Each has 200 or more taste
buds
Individuals vary in their
sensitivity to taste sensations,
a function of the density of
these papillae on the tongue.
Taste Buds
Each taste bud pore has 50-100
taste receptor cells with antenna
like hairs that sense food
molecules
(a) Taste buds line the trenches around tiny bumps on the tongue called papillae.
There are three types of papillae, which are distributed on the tongue as shown in
(b). The taste buds found in each type of papillae show slightly different
sensitivities to the four basic tastes, as mapped out in the graph at the top. Thus,
sensitivity to the primary tastes varies across the tongue, but these variations are
small, and all four primary tastes can be detected wherever there are taste
receptors. (Data adapted from Bartoshuck 1993a).
Taste
Taste receptors reproduce themselves every week or
two (this is why it hardly matters if you burn your tongue
with hot food).
As you grow older, the number of taste buds decreases,
as does taste sensitivity.
Taste
As with other senses, your experiences
influence your brain’s response.
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If you are told something is going to taste bad, your
brain responds more negatively.
Reversely, drinking coffee from your favourite cup will
taste 10-20% better
Likewise, being told that a wine costs $90 rather than
its real $10 price makes an inexpensive wine taste
better and triggers more activity in a brain area that
responds to pleasant experiences.
As happens with the pain placebo effect, the
brain’s thinking frontal lobes offer information
that other brain regions act upon.
Receptors for a given taste on apical
surface of taste cells
Gustatory pathway
Gustatory pathway starts with gustatory cell of the taste
bud (not with a neuron)
First synapse is the one between the basal surface of the
sensory cell and primary afferent axon (bodies of the 1st
neuron are in sensory ganglia of the CN. VII, IX, X (g.
geniculi ext., g. petrosum, g. nodosum)
N. VII inervates the first 2/3 of tongue surface, N. IX
posterior 1/3, and N. X small number of taste buds on
epiglottis
Central processes of these neurons end on rostral,
“gustatory” pole of the solitary nucleus (polus gustatorius n.
solitarii) (2nd neuron of the gustatory pathway)
Collaterals of these axons end up on the salivatory nuclei
(for secretion of saliva) and dorsal vagal nucleus (reflex
secretion of gastric juices)
Gustatory pathway cont.
Most of the axons of the 2nd neuron of the gustatory
pathway project to n. parabrachialis medialis in
the lateral tegmentum, where is the soma of the 3rd
neurona
Aksons of the 3rd neurona ascend through medial
part of the LM into ipsi- and contralat. VPM
thalamic nucleus (pars parvocellularis); smaller
portion of axons of the 2nd neuron come directly to
VPM th. n. (so, in th. is 3. or 4. neuron of the path)
Thalamocortical “gustatory” projection end up
inBA43 (ventral surface of the juncure of pre- and
postcentral gyrus in the ‘roof’ of the lateral sulcus of
Sylvius) (4. or 5. neuron of the gustatory path)
Osmoreceptors
Most of the osmoreceptor neurons are
located in OVLT (organum vasculosum
laminae terminalis), where the capilaries of
the BBB are fenestrated (hypovolemic thirst)
These neurons project on vasopressin
neurons in n. supraopticus and n.
paraventricularis on the anterior
hypothalamus (which themselves have
osmoreceptors that react on osmotic stimuli
and changes of Na concentration in blood)
Olfaction
Our Sense of Smell
What's in a
name? That
which we call a
rose by any other
name would
smell as sweet.
William
Shakespeare
How Olfaction Works
Smell (Olfaction): operates much like the sense
of taste.
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The physical stimuli are chemical substances carried
in the air that are dissolved in fluid, the mucus in the
nose.
Pathway: Olfactory cilia -> neural impulse -> olfactory
nerve -> olfactory bulb (brain)
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Olfactory receptors (olfactory cilia) and are located in the upper
portion of the nasal passages.
The olfactory receptors instantly alert brain through axon fibers
the brain.
Olfaction is the only sense that is not routed through the
thalamus.
This suggests that smell develops earlier than the other
senses.
How Olfaction Works
Receptor proteins are embedded on the surface
of nasal cavity neurons
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As a key slips into a lock  odor molecules slip
into receptors
Some odors trigger a combination of receptors
Odors are not easily classified.
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Humans can distinguish among about 10,000 odors,
but for some reason have a hard time attaching
names to odors quite frequently.
Chemoreceptors of the
olfactory system
- Olfactory epithelium consists of 3 types of
cells
- Primary aferent (bipolar) neurons are
constantly renewed from basal cells (every
30 days); their 10-20 immovable ciliae
contain olfactory receptor molecules
- Whole olfactory pathway is fully ipsilateral
Bipolar cells (1.)
Olfactory pathway
Mitral and tufted cells
(2.) in the olf. bulb
3. Their axons make olf.
tract which divides into
med. i lat. olf. stria
making trigonum olf. in
which we see
tuberculum olf.
Cortex praepiriformis
(primary olf. cx), n. olf.
ant.,
cx periamygdaloideus,
etc.
Kandel, 2000
100 snopića
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Buck, Linda and Axel, Richard
(1991) A novel multigene family
may encode odorant receptors: a
molecular basis for odor
recognition. Cell, 65, 175-187.
6 milijuna
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>1000 gena za rec. mirisa
(7 TM) = >3 % genoma
Mitral cells are principal neurons
of the olf. bulb. Their primary
apical dendrite extends into
spherical glomerulus (about 25
mitral cells converge to one
glomerulus), which accepts
axons primary olfactory neurons.
Axons of mitral cells make tzv.
lateral olfactory tract. These
axons give collaterals involved
in pos. and neg. feedback
control.
The architecture of the bulb
results in 1:1000 convergence of
olfactory receptor neurons to
mitral cells. Thus a lot of
information about individual
receptors is thrown away but
this increases sensitivity since
contributions from many
receptors are added together.
Centrifugal pathways have a "wipe clean"
function to reset the system ready for the
next input and also with disinhibition.
When hungry smells have a greater
effect!
Olfactory pathways
Most important projections of
the praepiriform cx:
- Orbitofrontal cx
(discrimination of odors)
- Mediodorsal th n. (pars
magnocellularis), also projects
to orbitofront. cx
- basal telencephalon, proand entorhinalni cx, hipp.
formation, lat. hipoth. (through
n. accumbens septi): affective
component of smell (“Prousts
phenomenon”, + aura – olf.
halucinations)
Olfactory system
– interesting facts
Most odor molecules have mol. mass less
than 350 kDa
Night butterflies can smell single molecule
of bombicol (pheromone)
Polar bears can detect a seal or whale
carcass from as far away as 32-60 km
Smell in space
Research has shown that your olfactory sensitivity
depends upon body position. Lie down, and you become
less sensitive. [Lundstrom et al., (2006) "Sit up and smell
the roses better: olfactory sensitivity to phenyl ethyl
alcohol is dependent on body position". Chemical
Senses 2006.
Although they give a number of reasons for this
phenomenon, it may be as simple as the decreased
effect of gravity on the blood pressure, as in astronauts.
Astronauts tend to lose their senses of smell and taste.
This is thought to be because to the congestion in the
nose resulting from the increased capillary pressure as
the heart no longer has to work against gravity. As a
consequence the sinuses tends to fill up with fluid, giving
rise to a feeling of stuffiness similar to a head cold.
Menstrual synchrony and smell
Armpit swabs taken from donor women at a certain phase in their
menstrual cycle and wiped on the upper lip of recipient women can
advance or retard menstruation in the recipients depending upon the
phase of the donor (Stern & McClintock, Nature (1998) 392, 177179):
They found that odourless compounds from the armpits of women in
the late follicular phase of their menstrual cycles accelerated the
preovulatory surge of luteinizing hormone of recipient women and
shortened their menstrual cycles. Axillary (underarm) compounds
from the same donors which were collected later in the menstrual
cycle (at ovulation) had the opposite effect: they delayed the
luteinizing-hormone surge of the recipients and lengthened their
menstrual cycles.
By showing in a fully controlled experiment that the timing of
ovulation can be manipulated, this study provides definitive
evidence of human pheromones.
Attractiveness of men's faces
in relation to women's phase of menstrual cycle
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In between-subjects studies on two groups of women of the
same age, we show that women assess male's facial
attractiveness differently in the follicular (F) and luteal (L)
phases. In the high conception risk phase (F), women tended to
give higher scores to male faces than when they were in the
luteal phase. During the five first days of the cycle, i.e. when the
estrogen level is still low, women assessed men's facial
attractiveness relatively highly. We suggest that it is
progesterone in the luteal phase that is responsible for lower
attractiveness assigned then to male faces. We also tested
which anthropometric facial traits or indices influence male
attractiveness.
We found that assessments of attractiveness were correlated
only with mouth height (positively) and the angle between the
middle of the mouth and the middle of the eyes (negatively).
Danel D, Pawlowski B, Coll Antropol. 2006 Jun;30(2):285-9
Smell of fear
Dogs and horses can smell fear in humans. Work by
Denise Chen (Chen & Haviland-Jones, Physiology and
Behaviour 1999; 68: 241-250) has demonstrated the
ability of underarm odour to influence mood in others.
Karl Grammer, in Vienna, has recently demonstrated
that the smell of fear can be detected (by women) in the
armpit secretions of people who watched a terrifying film
(Ackerl, Atzmueller & Grammer, Neuroendocrinol Lett
2002; 23(2): 79-84). The implication of this work is that a
chemical signal is secreted in sweat which
communicates the emotion.
Pheromones
In many animals, the sense of smell is used for
communication. For example, insects such as ants and
termites and vertebrates such as dogs and cats
communicate with each other by secreting and detecting
odorous signals called pheromones – especially to signal
sexual receptivity, danger, territorial boundaries, and food
sources.
We humans seem to use the sense of smell primarily in
conjunction with taste to seek and sample food, but some
evidence exists to suggest that people may also use
sexual pheromones as well as pheromones that help us
identify family members by smell.
For more information:

Video “Sweaty T-Shirts and Human Mate Choice”
for an evolutionary perspective on pheromones
Fragrance Effects
Research suggests that pleasant scents may trigger pleasant moods
and give a boost to workers’ performance.
Social psychologist Robert Baron, who has studied these fragrance
effects, has patented and is marketing a device that emits pleasant
scents. Called PPS (Personal Productivity/Privacy System) it
combines fragrance release with a whitenoise generator and an air
filter.
After testing dozens of smells, Baron found that lemon and light floral
had broad appeal (pine was the least popular odor), and is marketing
discs producing these odors with the PPS.
On a much larger scale, Shimizu Corporation has also patented an
“odordelivery” for commercial buildings. For example, it pumps a
citrus odor through an office building’s ventilation ducts every two
minutes. “The fragrance sense can be fundamental to controlling
conditions for office workers,” says Junichi Yagi, a representative for
Shimizu. He cites a month-long study of Japanese keypunchers in
which those who inhaled a lemon aroma make 54 percent fewer
errors than those who sniffed plain air. While the citrus odor seemed
to make people more alert, other smells, such as spiced apple,
seemed to aid relaxation.
Vomeronasal organ