3. Taste Receptor
• Receptor that facilitates the sensation of taste.
• When food or other substances enter the mouth
• Molecules interact with saliva and are bound to taste
receptors
• Present in Oral cavity and throat.
• It is type of chemoreceptors that is present on taste buds
• Taste buds- epithelial cells that act like neurotransmitters
• Innervated by cranial nerves
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4. Taste
• Taste (‘gustation’) is often referred to as the chemical senses
• They are mediated in the first instance by receptors that are
stimulated by chemical substances.
• Receptors are called ‘ chemoreceptors
• Taste: Chemicals dissolve in our mouth (must be water soluble)
and stimulate the taste buds in the oral cavity (tongue, soft
palate, cheek, etc.).
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5. Types of Tastes
Taste = ‘Gustation
Basic tastes:
1= Sweetness - outer tip of tongue
2= Saltiness - lateral edge of tongue behind tip
3= Sourness - lateral edge of tongue behind saltiness region
4=Bitterness - back edge of tongue toward throat
5= Umami - taste of glutamate - not localized
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7. Four Major Sensations of Taste
• Sweet- G-protein activates second messenger system
• Bitter- also G-protein activated specific receptor
• Sour- proton channel (acids taste sour)
• Salty- sodium channels Tastes seem to be enhanced in different
parts of the tongue
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9. Organ of Taste
• The tongue is the major organ of gustation
• There are also some taste buds on the palate, pharynx, and
epiglottis
Papillae - contain taste buds
• Fungiform papillae (mushrooms) - top surface of tongue
• Foliate papillae (ridges) - rear, lateral margin of tongue
• Vallate papillae (pimples) - rear, medial margin of tongue
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11. Taste buds
• Only 1% of the epithelial cells on tongue’s surface are taste buds
• Contain 50 to 75 sensitive cells each
• Taste-sensitive cells have a limited lifetime, and are constantly being
replaced.
• Taste pore permits substances to enter
• Three cell types in each taste bud:
• Taste receptors – chemoreceptors
• Basal cells - source of new taste receptors
• Gustatory afferent fibers - conduct action potentials to brain
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12. Taste cells – Taste Receptors
• Come from the division and differentiation of the basal cells
• Not neurons in the strict sense, but have synapses with gustatory afferent
fibers
• Arrival of chemical molecules on surface leads to change in membrane
potential - receptor potential
• Most taste receptors respond to at least two of the basic tastes
• Sometimes taste receptors generate action potential
• Transduction differs for each type of taste receptor
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13. Neural Pathways for Taste
• Afferents
• Anterior 2/3 of tongue - VII (facial nerve)
• Posterior 1/3 of tongue - IX (glossopharyngeal nerve)
• glottis, epiglottis, pharynx, palate - X (vagus nerve)
• All afferent fibers end in gustatory nucleus in the medulla
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14. Pathways to the Brain
• Taste fibers proceed along several pathways to the medulla oblongata or
brain stem, then to the thalamus, and finally to the taste area on the
anterior cortex.
• For taste sensation, gustatory nucleus neurons send fibers to the ventral
posterior medial nucleus (VPM) of thalamus
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15. Pathways to the Brain
• VPM sends fibers to the primary gustatory cortex ( Brodmann's area 43
in ventral parietal lobe
• For autonomic functions, gustatory nucleus sends fibers to the many
brainstem regions involved in swallowing, salivation, gagging, vomiting,
digestion, respiration and to the hypothalamus and amygdala
• appetite and food preferences
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16. Clinical Considerations
• Ageusia:
Absence of sense of taste
• Dysgeusia:
Disturbed sense of taste
• Hypogeusia:
Diminished sense of taste
• Hypergeusia:
Increased sense of taste
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