3. In the course of evolution,the most useful role of
taste possibly was to warn the animals against
harmful foods.Poisonous plants are frequently bitter
to taste
4. 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 ion
concentration .The cations of salt especially sodium cations, are
mainly responsible for the salty
5. 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 taste
sensation
5. Umami Taste – Japanese work (meaning “delicious”)
designating a pleasant taste sensation . It is dominant in food
containing L-glutamate
6.
7. A. Receptors - Taste Buds ( Sustentacular cells and
Taste cells)
9. Gustation:
• Sensation of taste.
Epithelial cell
receptors clustered in
barrel-shaped taste
buds.
• Each taste bud consists
of 50-100 specialized
epithelial cells.
Taste cells are not
neurons, but
depolarize upon
stimulation and if reach
threshold, release NT
that stimulate sensory
neurons.
10. Each taste bud contains taste cells responsive
to each of the different taste categories.
A given sensory neuron may be stimulated by
more than 1 taste cell in # of different taste
buds.
One sensory fiber may not transmit
information specific for only 1 category of
taste.
Brain interprets the pattern of stimulation with
the sense of smell; so that we perceive the
complex tastes.
11.
12.
13.
14. Location of Taste Buds – found on three types of papillae in
the tongue (Guyton)
1. Walls of the troughs that surrounds the Circumvallate papilla
which 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
15. Also in the mucosa of the epiglottis, palate, and
pharynx
(Ganong)
1. Fungiform papilla – numerous at the tip of the
tongue
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
16. 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
17. Mechanisms of Stimulation of Taste Buds
Receptor Potential
* For sodium 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
* For sweet 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
18. * Taste buds from the anterior 2/3 of the tongue > Chorda
tympani branch of Facial 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
19.
20.
21.
22. Salty:
• Na+
passes
through channels,
activates specific
receptor cells,
depolarizing the
cells, and
releasing NT.
Anions associated
with Na+
modify
perceived saltiness.
Sour:
• Presence of H+
passes
through the channel.
23. Sweet and bitter:
• Mediated by
receptors
coupled to G-
protein
(gustducin).
24. SVA (Special Visceral Afferent): Cranial Nerve VII, IX, XSVA (Special Visceral Afferent): Cranial Nerve VII, IX, X
29. Abnormalities of Taste
1. Ageusia – absence of taste sensitivity
2. Hypogeusia – diminished taste sensitivity
3. Dysgeusia – disturbed sense of taste
30. Substance Taste Threshold Concentration ( mol/L)
Hydrochloric acid Sour 100
Sodium chloride Salt 2000
Strychnine hydrochloride Bitter 1.6
Glucose Sweet 80,000
Sucrose Sweet 10,000
Saccharin Sweet 23
Taste Thresholds & Intensity Discriminations
The ability of humans to discriminate differences in the intensity of
tastes, like intensity discrimination in olfaction, is relatively crude. A
30% change in the concentration of the substance being tasted is
necessary before an intensity difference can be detected. The
threshold concentrations of substances to which the taste buds
respond vary with the particular substance (Table 10–2).
