Gust at Ion
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Transcript of Gust at Ion
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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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