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TasteTasteSensationSensationTasteTasteSensationSensation

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The senses of taste and smell allow us to separate

undesirable or even lethal foods from those that arepleasant to and nutritious

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A.Stimulus Sapid substance or substances with

taste

Primary Sensations of Taste

1. Sour Taste caused by acid (hydrogen ion concentration.

Intensity of sensation is proportional to the logarithm of the

hydrogen ion concentration

2. Salty taste elicited by ionized salts, mainly by sodium ionconcentration .The cations of salt especially sodium cations, are

mainly responsible for the salty

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3. Sweet Taste is not caused by any single class of

chemicals. Includes sugars, glycols, alcohols, aldehydes,

ketones, amines, esters, some amino acids etc.

4. Bitter Taste Like sweet taste is not caused by any single

type of chemical agent. Long chain organic substances that

contain nitrogen and alkaloids are likely to causes bitter tastesensation

5. Umami Taste Japanese work (meaning delicious)

designating a pleasant taste sensation . It is dominant in food

containing L-glutamate

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A. Receptors - Taste Buds ( Sustentacular cells and

Taste cells)

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Taste BudTaste Bud

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Gustation: Sensation of taste.

Epithelial cellreceptors clustered in

barrel-shaped tastebuds.

Each taste bud consistsof 50-100 specializedepithelial cells.

Taste cells are not

neurons, butdepolarize uponstimulation and if reachthreshold, release NTthat stimulate sensoryneurons.

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Each taste bud contains taste cells responsiveto each of the different taste categories.

A given sensory neuron may be stimulated by

more than 1 taste cell in # of different tastebuds.

One sensory fiber may not transmitinformation specific for only 1 category oftaste.

Brain interprets the pattern of stimulation withthe sense of smell; so that we perceive thecomplex tastes.

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Location of Taste Buds found on three types of papillae inthe tongue (Guyton)

1. Walls of the troughs that surrounds the Circumvallate papillawhich form V line on the posterior tongue

2.Fungiform papillae over the flat anterior surface of the

tongue (moderate number)

3. Foliate papillae located in the folds along the lateral

surfaces of the tongue (moderate number)

Additional taste buds are located on the palate, tonsillar

pillars, epiglottis and proximal esophagus

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Also in the mucosa of the epiglottis, palate, andpharynx

(Ganong)

1. Fungiform papilla numerous at the tip of thetongue

2.Vallate (circumvalate ) papilla arrange on the

back of the tongue

3. Filiform papilla cover the dorsum of the tongue , do not

usually contain taste buds

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Specificity of Taste Buds for a Primary Taste

Stimulus

Each taste bud usually responds mostly to one of the

five primary taste stimuli when taste substance is in

low concentration.At high concentration, most buds

can be excited by two or more of the primary taste

stimuli

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Mechanisms of Stimulation of Taste Buds

Receptor Potential

* Forsodium ions and hydrogen ions, which elicit salty and

sour sensations, respectively, the receptor proteins open

specific ion channels in the apical membranes of the taste

cells, thereby activating the receptors

* Forsweet and bitter taste sensation the receptor protein

molecules activate the second-messenger transmitter

substances inside the taste cells and these second

messengers cause intracellular chemical changes that elicit

the taste signals

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* Taste buds from the anterior2/3 of the tongue > Chorda

tympani branch ofFacial Nerve.

* From posterior third of the tongue > Glossopharyngeal nerve* From tonsillar areas and back of the tongue > Vagus Nerve

Tractus Solitarius (medulla oblongata) > Medial Lemniscus

> Thalamus

Center Postcentral Gyrus

Adaptation of Taste Extreme degree of adaptation that

occurs in the sensation of taste almost certainly occurs in the

central nervous system

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Salty:

Na+ passesthrough channels,activates specific

receptor cells,depolarizing thecells, andreleasing NT.x Anions associated

with Na+ modifyperceived saltiness.

Sour: Presence of H+ passes

through the channel.

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Sweet and bitter:

Mediated by

receptors

coupled to G-

protein

(gustducin).

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SVA(Special Visceral Afferent): Cranial Nerve VII, IX, XSVA(Special Visceral Afferent): Cranial Nerve VII, IX, X

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Modality:Modality: Taste SensationTaste Sensation

Receptor:Receptor: Taste BudTaste Bud

Cranial Nerve: VII, IX, XCranial Nerve: VII, IX, X

1st Neuron:1st Neuron:GeniculateGeniculate Ganglion (VII)Ganglion (VII)

Inferior Ganglion (IX, X)Inferior Ganglion (IX, X)

2nd Neuron:2nd Neuron: NucleusNucleus TractusTractus SolitariusSolitarius

(Gustatory Nucleus)(Gustatory Nucleus)

solitariothalamicsolitariothalamic fiber (centralfiber (central tegmentaltegmental tract)tract)

3rd Neuron:3rd Neuron:Thalamus (Thalamus (VPMpcVPMpc))Internal CapsuleInternal Capsule ---------- CoronaCorona RadiataRadiata

Termination:Termination:Gustatory AreaGustatory Area

BrodmannBrodmann area 43 &area 43 & parainsularparainsular cortexcortex

Taste (Gustatory) PathwayTaste (Gustatory) Pathway

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Taste PathwaysTaste Pathways

A. nucleus tractusA. nucleus tractus

solitariussolitarius

(gustatory nucleus)(gustatory nucleus)B. thalamus (VPMpc)B. thalamus (VPMpc)

C. Brodmann area 43C. Brodmann area 43

D. parainsular cortexD. parainsular cortex

E. parabrachialE. parabrachial

nucleusnucleus

1. solitariothalamic1. solitariothalamic

fiber (centralfiber (central

tegmental tract)tegmental tract)

2. corona radiata2. corona radiata

VII. facial nerveVII. facial nerve

IX. glossopharyngealIX. glossopharyngeal

nervenerve

X. vagus nerveX. vagus nerve

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Transmission of Signals into the Central Nervous

System (Conducting Pathway)

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Abnormalities of Taste

1. Ageusia absence of taste sensitivity

2. Hypogeusia diminished taste sensitivity

3. Dysgeusia disturbed sense of taste

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