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ORAL PHYSIOLOGY

GENERAL SENSATION IN THE ORAL CAVITY (PART II)

12th MARCH 2012

Taste Bud Cells(continue from last lecture)

Last time we talk about taste bud cells. And we said that taste bud cells located in

a structure of taste bud. So the taste bud is histological structure that contains anumber of cell. So for example, here we see a representation of taste bud. These

taste bud is located within the epithelium and it response to the chemical brought

to this taste bud by saliva. So saliva is important for taste. People without saliva

will have decrease taste. Why? Because saliva is the vehicle through which the

taste material travels to reach taste bud. So thats why in order for you to taste

the chemical or different taste material, they should be in saliva.

So saliva reaches this area here which is the taste pore.

And we have different cells. All of this is epithelial cell that subject to turnover

every 2-30 days. So there is big change every 2-30 days and thats why the

turnover rate is very high. This means that the cells are very active. So cells with

high turnover rate are active cells. We have type I, II, III, IV.

Type I (please refer to the picture/slide).

It is located at the periphery of the bud. Thats why we see taste bud type I. 2/3 of

the cell are of type I. They are called dark cells because they stain dark (accept

dark stain). You can see granules; these granules claim to secrete the poresubstance. Here the pore area is filled with material which called pore substance.

It is believed that type I cell they secrete the pore material. Thats why they have

granules. The end of the bud pore, they have microvilli to increase the surface of

secretion. The basal end then reaches down to the basement membrane. This is

important, see here this cells reach the pore and also they reach the basement

membrane here. Not all cells reach the basement membrane. Next, have lateral


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extension extending across the other cells and nerve fibrils and they have

invaginated apical nucleus. As you see, the nucleus is invaginated, its not

rounded, and it is located apically, not laterally. Some located closed to the

basement membrane.

Type II

They have also microvilli, but these are thick microvilli, they contain a number of

vesicles. They have smooth walled apical nucleus. The nucleus is located also

apically but not invaginated. They make up 20% of bud cells and do not reach

apical basement membrane as you see, this cell are short and they do not show

any synaptic like features. They dont have any connection with nerves

Type III

They are peg like cell, no microvilli and appear to synapse with adjacent nerve

fibers. They are not shown here. They make connection with nerves

Type IV

They are progenitor cell, means these are the cell that give branch to different cell

like type I, type II and type III

Sensory mechanism of taste

The substance that stimulate taste sensation is called sapid. Gustation is the

process involved in taste perception. For example the process involved in pain

reception is nociception, but the process involved in the taste perception is

gustation. Any material to be classified as sapid need to be dissolved in water or

saliva. It should also react with pore content and bud cells

Gustation theory

Old theory says the inhibition or potentiation of the pore enzyme lead to changes

in receptor cell.

The more acceptable theories , it says that changes in membrane permeability of

receptors or nerve fibers resulting from binding of excitatory substances leading


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ORAL PHYSIOLOGY


12th MARCH 2012

to action potential which the new theory, it says that these cells (the cells of taste

bud) are the receptors. So we have something like action potential in the wall of

these cells that makes impulse that travel through neurons to the brain.

Question : the old theory saying that the receptor cells found in the taste bud

cell?

Answer: the taste bud cells are the cells that receive information. But the thing is,

do we have action potential running through these cells or not? The old theory

says no. No action potential running through the wall of these cells. But these

cells respond to some enzymes located in the taste bud pore.

The more acceptable theory says no. We have action potential that runs through

the wall of these cells like ____nose straightaway and then they travel

information to the nose and then to the brain.

Gustatory Pathway

All the time runs through autonomic pathways are sympathetic and

parasympathetic particularly parasympathetic of course. These are small

myelinated slowly-conducting axons. They make synapse at nucleus of tractus

solitarius. *The doctor said dont worry about this because it is knowledge about

neuron.The 2 neurons, they cross midline in medial lamniscus and then to the thalamus.

The 3 neurons to the lower part of postcentral gyrus as we said. Why? Because

we said that this area is the area of the tongue of lower part of postcentral gyrus.

This mean, if you want to taste something on the right side of your tongue, the

information that travels about nerve taste in your brain travels to left side of your

brain. Because we have crossing the midline at the level of the 2 neurons. This is

actually as an example if you want to taste things here this is one side of the head

and then the 1st

of the neuron does not cross the midline, 2 neuron crosses themidline, and 3

rdof the neuron does not cross the midline. So thats why the area

responsible for taste about right is left side area and vice versa.


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Classification of Taste

Henning has four types of tastes; salt, sweet, sour and bitter. But actually we have

also many types of taste in between. One student raises his hand and says,

yesterday I ate something which is sweet, and bitter at the same time. Ginger for

example. Ginger is bitter but also you can taste something sweet. Asian people

are very famous of ginger, they use ginger in their food. Avocado is another

example. Is avocado sweet? I feel it sweet but also theres some bitter taste in

avocado and also we have something sour and something salty. So thats why we

have taste that are difficult to describe. So this means, we have also, its not

necessarily that we have all sweet, sour and bitter but we have, we make up a

combination of these taste. You think about this like we have tetrahedron, at the

edge/angle of this tetrahedron, each angle represent one of these tastes. So we

have salt, sweet, sour and bitter. And between over inside the area between

these points can have any combination of taste.

So thats why these represents the, lets say the extreme of taste type. So they

didnt talk about modalities of taste but extreme of taste type corners of taste

tetrahedron as we said. All tastes being inside of tetrahedron and in addition to

that sometime you might feel something slimy like alkaline or metallic tastes

which are not among taste categories. They are not classified as taste categories.

Taste buds vary in sensitivity. A few respond to one taste modality. Most respond

to more than one and one modality is dominant.

If you go back here to this one here .We said bitter is sense at the posterior part

of the tongue . Do you think if I put something sweet here, I will not taste it? I will

still taste it! You can try that. Put a piece of sugar at the back of your tongue, and

you will still sense it but if you put this piece of sugar at the tip of your tongue,

you will feel its sweetness more, you will feel more sweet. This means that any

taste buds can respond to any of these taste materials but we have taste buds

that are more sensitive to certain types of taste . So taste buds located at the

front of the mouth respond better to sweet. They respond less to salt less to acid

and least to bitter and so on. Ill give you and example, I am a dentist ok , and Ican do anything in dentistry alright? But maybe in endodontist, its better for me

in dealing with root canal treatment. Thats why all taste buds respond to all

different and separate materials but it has sensitivity inside these taste buds to

different sapid materials. Usually one modality is dominant. We usually say for

taste bud making the bitter taste is a dominant taste but how do you respond to

acidic material?


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Acid Taste

Tasting acid leads to release of hydrogen ions. These hydrogen ions block

potassium channel and lead to depolarization. So this is the theory behindresponding to acidic taste. Inorganic acid taste metallic, usually in organic acid

they taste fruity.

Salt Taste

What about salt taste? Simulation of receptors by cations, cation is a positive ion,

we have cations and anions. The gustant type is NaCl. The salt taste is NaCl,

Sodium chloride. What about this NaF? It usually tastes less salty than NaCl, so

thats why we suggesting model salt taste, NaCl. In low concentration, we feel

sweet instead of salty, we usually eat something salty but in very low

concentration ,you feel sweet and salty .Thats why when we have low

concentration sweet ,we usually have Potassium chloride and potassium sulfate

instead of NaCl. The possible theory of salt perception, they say that opening of

sodium channel lead to depolarization because any low concentration sweet

contain sodium or sometimes potassium.

Sweet Taste

Now what about sweet taste? What is certain type of sweet taste and what is

model for sweet taste which is sucrose, its not glucose btw. Chemical similarities

between sweet and bitter sapid materials. Material closing sweet very close in

chemical reaction to material closing bitter btw. The other substances that can

make : some amino acid , lead acetate, chloroform, saccharin and cyclamate.

Sucrose is not desirable and you have to be aware that sucrose is cariogenic. We

have cariogenic sweeteners like sugar alcohol -sorbitol , xylitol and these are use

in diet materials. Common chemical feature of sweet taste - producing materials,

we have covalent hydrogen bond which is loosely attach to 2nd

group long

distance which is binds to a mirror image conformation on the receptor

membrane leading to closure of K channel depolarization. Dont worry about

the details. Just remember the final step which is closure of K channel which leads

to depolarization.


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Bitter Taste

The bitter taste, gustant type is quinine. This has therapeutic value it is use as

medication and use in many alkaline drinks. Other stimulant sapid materials that

close bitter taste include Alkaloids, Glycosides, Picric acid, Nitrus and sulphide

groups, Mg sulphate, Calcium oxide. Bitter tasting substances are harmful or

poisonous. Thats why taste is used as warning to animal. Only human can

withstand to bitter taste. Eg coffee is bitter but its nice. Try giving your cat coffee.

Of course your cat will not withstand to it because its bitter. Your cat will think

that this thing is poisonous .Common chemical feature of bitter taste- producing

substances , it is similar to the sweet taste mechanism as we said at the beginning

here, we have covalent hydrogen bond loosely attached to a second group with a

shorter distance, while in sweet taste we have long distance. The cellular

mechanism of stimulation is not well understood yet.

Flavor

What is the different between taste and flavor? Flavor is the total sensation

induced when a particular foodstuff is introduced into your mouth. So thats why

taste is the major component of flavor. Flavor is bigger than taste. Because flavor

depends on simultaneous stimulation of olfactory, touch receptors in the palate

and reactions to irritants on the lingual surface. Example when you want to eat an

apple, and you put the apple inside your mouth of course the materials in that

apple will make reaction with your taste buds to induce taste. But at the sametime, you will smell that apple. So smell plus taste make flavor. If you want to

appreciate the role of flavor, try eat an apple when you have common cold. Now

you will feel the taste of that apple is different. It is not the taste because taste is

based on stimulation of taste buds. So taste buds stimulations happened when

you have cold or not. But what happened? You lose the action of olfaction. So the

flavor going to change.

We also have other factors associated with flavor. Remember flavor is not only

taste plus olfaction. Its more than that. Olfaction is one of the factors.The touch receptors in the palate also are important because sometimes when I

put an impression material (material use in dentistry) in your mouth, you feel the

flavor of alternate because it has come in contact with the touch receptors in your

palate. Also we have the reactions to irritants on lingual surface are also classified

among flavor. Ill give you an example. Chilly, mustard, pepper, ginger, they


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ORAL PHYSIOLOGY


12th MARCH 2012

stimulate nocireceptors of trigeminal nerve and they leave the feeling of hot

flavor or spicy flavor. Thats why it is wrong to say we feel hot taste or spicy taste.

Because taste can only response to sweet, sour, salt and bitter or the combination

of these. But when you eat something hot or something spicy, it is not taste. It is

flavor.

Adaptation of taste perception

Do you think that you will taste the sweetness of tea? No. Why? Because there is

something called adaptation. If the stimulation continues, if you eat something

sweet then your brain will be adapted to that sweet taste. Thats why you need abig concentration of something sweet to induce the same effect. So thats why

sweetness is considered as something acquired. It is absent or weakly present in

infants.

Factors Affecting Pain Perception

Now this slide is also important.This is the last slide but also the most important

slide.

1.

Oral temperature If you eat something cold, this leads to reduction in receptor ability.

Thats why when you decrease temperature, the amount of

perception decrease.

When you increase temperature, the amount of perception increase. For example, when eating an ice cream, it is very cold. Try to melt the

ice cream and to eat it. It will taste extremely sweet. Why does this

happen? Since ice cream is best eaten when its cold, they need to

put a big amount of sugar in that ice cream and then freeze it then

only you can eat it. That means anything that is sweet and cold would contain a big

amount of sugar.

2. Combination of gustants It is a perception when you taste a combination of gustants like

sweet, sour or salty. It is hard to explain.


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Example is when you eat something like dates? (Im not sure what isthe example, its not clear!)

3. Hormones4. Age

As you grow older there will be a reduction in taste perception.5. Genetic factors6. Deprivation from salt

This leads to low threshold to NaCl7. Dehydration

It has the opposite. Threshold to NaCl becomes higher. This is important as it has beneficial modification which is getting the

body need of salt.

8. Cigarette smoking It diminishes taste perception to all kind of taste. Smokers will have better perception to bitter taste.

9. Local anesthesia The salt and sweet taste are reduced Taste sensation is abolished to bitter, then salt, acid and sweet.

by MUNIRAH,AIN,AISHAH,NADHIRAH,IRISYAH

oral physio 5

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