The document discusses the human sense of taste. It describes the five primary tastes detected by taste buds located on papillae on the tongue. Taste buds contain specialized cells that detect tastes and transmit signals through cranial nerves to the brainstem, thalamus, and gustatory cortex. Factors that influence taste include saliva, medications, disease, and aging. Disorders of taste include loss of taste and distortions or phantom tastes.

1. TASTE PATHWAY

2. CONTENTS
• INTRODUCTION
• PRIMARY TASTE SENSATION
• TASTE BUDS
• PAPILLAE OF TONGUE
• TASTE PATHWAYS
• APPLIED ASPECTS
• CLINICAL CONSIDERATIONS
• CONCLUSION
• REFERENCES

3. INTRODUCTION
• Sense of taste-allow us to separate undesirable
or even lethal foods from those that are pleasant
to eat.
• Function of taste buds
• Taste stimulate secretion of saliva and gastric
juices.
• Allows to select food

4. Primary sensations of taste
2 Sodium Receptor
2 Potassium Receptor
1 Chloride Receptor
1 Adenosine Receptor
1 Inosine Receptor
2 Sweet Receptors
2 Bitter Receptors
1 Gluatamate Receptor
1 Hydrogen Ion Receptor

5. SOUR
SWEET
BITTERSALTY
UMAMI

6. SOUR TASTE
Concentration of H+ ions
Intensity α log of H+ ion
More acidic α more sour

7. SALTY TASTE
Elicited by ionized salts
Sodium ion concentration

8. SWEET TASTE
• Sugars
• Glycols
• Alcohols
• Aldehydes
• Ketones
• Inorganic salts of lead & beryllium
•Amides
•Esters
• Aminoacids
•Small proteins
•Sulfonated acids

9. BITTER TASTE
Long chain organic substances –
nitrogen
Alkaloids – drugs-quinine,caffeine
Deadly toxins found in poisonous plants
Rejection of food

10. UMAMI TASTE
Japanese word- ‘pleasant sevory taste’
Glutamate receptor
Kikunae Ikeda in 1908
Fish, mushrooms,aging cheese,
spinach, ripe tomatoes,meat extracts.

12. THRESHOLD FOR TASTE
• Sour taste
• HCl
0.0009N
• Salty taste
• NaCl
0.01M
• Sweet
taste
• sucrose
0.01M
• Bitter
taste
• quinine
0.000008
M

13. TASTE BUD
• Goblet shaped
• Diameter : 1/30 mm
• Length : 1/16mm
• 50 modified epithelial cells
Supporting cells Gustatory cells

15. • Appears early – 7 to 8 weeks of IUL
• Matures later after gestation
• Increase in number after birth
• Adults- 3000-10,000
• Children
• >45yrs
• Ability to Regenerate – gustatory nerve
Degenerate ---taste sensation

16. TASTE CELLS
• Mitotic division
• Mature cells- lie toward centre of the bud-break
up & dissolve
• Life span- 10 days

17. HISTOLOGY OF TASTE BUD
• Type 1 – long and narrow ,dark
cells,irregular nucleus
• Type II – long, light cells, round oval nuclei
• Type III – similar to type II , dense cored
vesicle in basal portion
• Type IV - contacts basement
membrane,doesnot extend to the taste pore
- basal cell

18. LOCATION OF TASTE BUDS

19. FILIFORM PAPILLAE

20. FUNGIFORM PAPILLAE

21. CIRCUMVALATE PAPILLAE

22. FOLIATE PAPILLAE

23. MECHANISM OF TASTE SENSATION
Taste cell membrane
- - - - - -
+ + + + + +
Taste substance
Depolarization
Receptor potential

25. • Generation of nerve impulses – strong
immediate signal
Weaker continuous signal
Exposed to stimulus

26. CENTRAL TASTE PATHWAY

27. Central Termination – Afferent Fibers
• Facial (VII) nerve- chorda tympani – entirely
gustatory
• Glossopharyngeal ( IX ) – gustatory & somato
sensory fibres
• Vagus (X ) – superior laryngeal nerve –gustatory
& chemosensory fibres

28. NTS
ROSTARL
ZONE –
gustatory
information
CAUDAL –
swallowing,
respiartion,
gastric motility
MEDIAL
LATERAL

29. • Three main types of neurons
• ELONGATE: fusiform cell body, 2 primary
dendrites
• MULTIPOLAR: stellate , pyramidal soma ,3-4
primary dendrites
• OVOID : small soma, 3 or more primary
dendrites

30. PONTINE TASTE RELAY
• Ascending axons bypasses –
ventroposteromedial nucleus of thalamus.
• Organised along dorsoventral axis
• Response characteristics - NTS

31. THALAMUS AND CORTEX
• Thalamic gustatory relay nucleus
ventro medial tip
ventro postero medial thalamic nucleus
part of ventro basal complex
• Projections further ascend – agranular insular
cortex
• Gustatory stimulation – cortical gustatory projection

33. ROLE OF SALIVA
• Essential for normal taste function
• Dry mouth- difficult to taste
• Acts as a solvent
• Fungiform – saliva from all salivary glands
• Remaining papillae – von Ebner’s
• Taste buds –palate,larynx,pharynx- minor salivary
glands

34. • Feeding/drinking
Muscles move food around mouth
Facilitates access of solubilzed taste stimuli entirely
• Significant – clefts of vallate & foliate papilla

35. Effect of reduced salivation
• Head and Neck radiation – taste disturbances
• Affect turn over of taste buds
• Damage nerve terminals
• xerostomia- altered taste perception

36. Salivary gland removal
Electronmicroscopy of taste buds
macrophages, large number of bacteria
altered taste perception
• Sjogren syndrome- reduced taste sensitivity for
all 4 taste qualities

37. CLINICAL CONSIDERATIONS
• Complete loss – aguesia
• Partial loss – hypoguesia
• Distortions of taste – dysguesia
• Abberant taste - Abnormal stimulation – Phantom –
chemosensory disorders
• Vitamin A deficiency - keratinization
• Gustatory hallucinations -epilepsy

38. • Familial dysautonomia – smooth tongue +
papillae taste buds
• Malignancy – anorexia
• Burning mouth syndrome
• Taste blindness- genetic - recognize taste
• Poor oral hygiene

39. Incidence of taste disturbance with common
medications
Medication Incidence , %
• Acetazolamide 12-100
• Captopril 2-7
• Lithium 5
• Procainamide 3-4
• Amiodarone 1-3
Rebecca Douglass et al, Drug-related taste disturbance A contributing factor in
geriatric syndromes; Can Fam Physician 2010;56:1142-7

40. INVESTIGATION
Possible causes
• Detailed history and examination - local causes.
• Haematological and biochemical investigations -
nutritional and endocrine causes
• Computed tomography - neurological causes
• Ageing process
J M Boyce, G R Shone, Effects of ageing on smell and taste; Postgrad Med J 2006;
82:239–241.

41. MANAGEMENT
• Counselling and reassurance
• Relatives or neighbours need closer involvement
to check for spoiled food that if eaten could lead
to food poisoning.
• Flavour enhancement - salt
J M Boyce, G R Shone, Effects of ageing on smell and taste; Postgrad Med J 2006;
82:239–241

42. CONCLUSION
• Taste sensation allow us to separate lethal foods
• 5 principal taste
• Mainly in taste buds
• Lack-anorexia, weight loss.

43. REFERENCES
• Bradley RM: Essentials of Oral Physiology,
USA,1998, Mosby
• Antonio Nanci. Salivary Glands. Tencate’s Oral
Histology 7th ed.Mosby .India. 2008
• G S Kumar.Salivary glands .Orban’s Oral
Histology and Embryology.12th ed.Elsevier
India;2007
• Arthur Guyton.The Chemical senses. Textbook
of medical physiology.10th ed WB Saunders;2001

44. • J M Boyce, G R Shone, Effects of ageing on smell
and taste; Postgrad Med J 2006;82:239–241.
• Rebecca Douglass et al, Drug-related taste
disturbance A contributing factor in geriatric
syndromes; Can Fam Physician 2010;56:1142-7