experiment 7 fua 1323

8/7/2019 Experiment 7 fua 1323

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INTRODUCTION:

Taste buds contain the receptors for taste. They are located around the small

structures on the upper surface of the tongue, soft palate, upper esophagus and

epiglottis, which are called papillae. These structures are involved in detecting the

five elements of taste perception: salty, sour, bitter, sweet, and savory). Via small

openings in the tongue epithelium, called taste pores, parts of the food dissolved in

saliva come into contact with taste receptors. These are located on top of the taste

receptor cells that constitute the taste buds. The taste receptor cells send

information detected by clusters of various receptors and ion channels to the

gustatory areas of the brain via the seventh, ninth and tenth cranial nerves.

OBJECTIVE:

1. To examine the part of the taste receptor on the human tongue.

2. To understand the role of taste receptors in the central nervous system

(CNS)

APPARATUSES:

1.

Petri dishes2. Cotton wool

3. Beaker

4. Toothpick

MATERIAL:

1. 10% NaCl

2. 10% Sucrose3. Orange juice

4. Commercial vinegar



PROCEDURE:

1. The mouth was washed thoroughly. Cotton wool was rolled on the end of a

tooth pick to make cotton buds.

2. A cotton bud was dipped in sucrose solution and touched on the as below

a- Tip of tongue b- Frontal edges of the tongue

c- Middle of the upper side of tongue

d- Middle of under side of the tongue

e- Back edges of the tongue

f- Frontal mid part of the under side

of the tongue.

E1 e4

E2 D e5

E3 e6

B1 C b3

B2 b4

F

A



3. The taste area of the tongue was drawn and marked the symbols marked

below:

+++ - Very sweet

++ - Sweet

+ - Less sweet

0 - No taste

4.

The mouth is washed with a new cotton bud and the experiment wasrepeated with the following solutions:

10% NaCl

Orange juice

Commercial Vinegar

5. The results were written as described in step 3 and the taste area for each

solution was drawn.



RESULTS:



DISCUSSION:

1. On average, the human tongue has 2,000±8,000 taste buds

2. Each taste cell has receptors on its apical surface. These are transmembrane

proteins which

Admit the ions that give rise to the sensations of salty and sour;

Bind to the molecules that give rise to the sensations of sweet, bitter, and

umami.

3. A single taste cell seems to be restricted to expressing only a single type of

receptor (except for bitter receptors).

4. Taste receptor cells are connected, through an ATP-releasing synapse, to asensory neuron leading back to the brain.

5. However, a single sensory neuron can be connected to several taste cells in

each of several different taste buds.

6. The sensation of taste ² like all sensations ² resides in the brain

7. These nerve endings transmit messages directly to the brain by chemical

reactions.

8. Another major component to taste is smell. With smell alone you can often

tell the difference in foods or drinks, while without smell it can be difficult

to distinguish between different tastes. You may notice this when you have acold or stuffy nose and food does not taste normal.

Salty

The receptors for table salt (NaCl) is an ion channel that allows sodium ions (Na+)

to enter directly into the cell. This depolarizes it allowing calcium ions (Ca2+

) to

enter [Link] triggering the release of ATP at the synapse to the attached sensory

neuron and generating an action potential in it.

In humans, the hormone aldosterone increases the number of these salt receptors.

his makes good biological sense:

y The main function of aldosterone is to maintain normal sodium levels in the

body.



y An increased sensitivity to sodium in its food would help an animal

suffering from sodium deficiency (often a problem for ungulates, like cattle

and deer).

Sour

Sour receptors are transmembrane ion channels that admit the protons (H+)

liberated by sour substances (acids) into the cell.

Sweet

Sweet substances (like table sugar ² sucrose) bind to G-protein-coupled

receptors (GPCRs) at the cell surface.

y Each receptor contains 2 subunits designated T1R2 and T1R3 and is

y coupled to G proteins.

y The complex of G proteins has been named gustducin because of its

similarity in structure and action to the transducin that plays such an

essential role in rod vision.

y The mechanism is similar to that used by our odor receptors [View].

The hormone leptin inhibits sweet cells by opening their K +

channels. This

hyperpolarizes the cell making the generation of action potentials more difficult.

Bitter

The binding of substances with a bitter taste, e.g., quinine, phenyl thiocarbamide

[PTC], also takes place on G-protein-coupled receptors that are coupled to

gustducin.

Humans have genes encoding 25 different bitter receptors ("T2R s"). However,

each taste cell responsive to bitter expresses many of these genes. (This is in sharp

contrast to the system in olfaction where a single odor-detecting cell expressesonly a single type of odor receptor.)

Despite this ² and still unexplained ² a single taste cell seems to respond to

certain bitter-tasting molecules in preference to others.



So it is the activation of hard-wired neurons that determines the sensation of taste,

not the molecules nor the receptors themselves.

CONCLUSION:

The tongue has taste buds contain the receptors for taste. They are found aroundthe small structures on the upper surface of the tongue, soft palate, upper

esophagus and epiglottis, which are called papillae. These structures are involved

in detecting the five types of taste: (salty, sour, bitter, sweet, and savory).

QUESTIONS:

1. Are the various parts of the tongue as sensitive to the different taste

stimulation given?

Yes , the various different parts of the tongue are sensitive to different typesof tastes.

2. It is the same receptor (or different) responding to various taste stimulation?

If the answer is YES, explain why.

Yes. This is because the number of molecules elicits tastes sensations

thorough a rather small number of taste receptors. It appeared that individual

taste receptor cells bear receptors for a few type of tastes type of taste.

REFERENCES:

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/T/Taste.html

http://en.wikipedia.org/wiki/Taste_bud

http://www.pamf.org/teen/health/skin/tastebuds.html

experiment 7 fua 1323

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