It is about our sensory organ

1. Taste
Dr. Berjin
Jr Resident
Department of Physiology

2. • The sense organ for taste is the taste buds
• About 10,000 taste buds
• Receptors for taste are called taste receptors
or gustatory receptors or taste cells

3. Structure of taste bud
• Ovoid in shape
• Made up of 4 types of cells:
• - Basal cells
• - Dark cells
• - Light cells
• - Intermediate cells
• The taste cells have
microvilli that project into the
taste pore
• Afferent fibres arise from the taste cells, each taste bud
is innervated by about 50 nerve fibres

4. Location of taste buds
• Taste buds are located in the mucosa of the
• Epiglottis
• Palate
• Pharynx
• Walls of papillae of tongue

5. Types of papillae in the tongue
1.The Fungiform papilla
2.The Circumvallate papilla
3.Foliate papilla

6. Types of papillae in the tongue
• Fungiform papillae – rounded structures near
the tip of the tongue (about 5 taste buds
each)
• Circumvallate papillae – arranged in a V in the
back of the tongue (about 100 taste buds
each)
• Foliate papillae : posterior edge of the tongue
(about 100 taste buds each)

8. Taste Pathway

9. Taste pathway
• The sensory nerve fibers from the taste buds on the anterior two-
thirds of the tongue travel in the chorda tympani branch of the facial
nerve
• Taste sensations from the posterior third of the tongue reach the
brain stem via the glossopharyngeal nerve
• The fibers from other areas other than the tongue (eg, pharynx)
reach the brain stem via the vagus nerve
• The taste fibres in the three nerves unite in the gustatory portion of
the nucleus of the solitary tract (NTS) in the medulla oblongata

10. Taste pathway
• From the nucleus of solitary tract, axons of second-order
neurons ascend in the ipsilateral medial lemniscus and
pass directly to the ventral posteromedial nucleus of the
thalamus
• From the thalamus, the axons of the third-order neurons
pass to neurons in the anterior insula and the frontal
operculum (primary gustatory area in the parietal lobe) in
the ipsilateral cerebral cortex

11. Basic taste Modalities
• Sweet
• Sour
• Salty
• Bitter
• Umami - taste sensation triggered by monosodium
glutamate, pleasant & sweetish

12. Any special areas on the tongue for
each taste sensation?
• All taste sensations are sensed from all parts
of the tongue

13. Taste thresholds and intensity
discrimination
• Most sensitive to taste receptors – Bitter
• Least sensitive to taste receptors – sweet
• A 30% change in the concentration of the
substance being tasted is necessary before an
intensity difference can be detected

14. Abnormalities of taste
• Ageusia : absence of sense of taste
• Hypogeusia : diminished taste sensitivity
– Causes : Damage to the lingual or glossopharyngeal
nerves, Bell’s palsy
• Dysgeusia or parageusia : Unpleasant perception
of taste : can be caused by the above factors

15. • Ganong ‘s review of Medical Physiology