This document provides information on the physiology of taste sensation. It begins with an introduction to taste buds and the sense of taste. It then describes the anatomy of the tongue, including the different types of papillae and taste buds. It explains the primary tastes detected, gustatory pathway, and mechanism of taste stimulation and transduction. Finally, it discusses applied physiology such as various taste disorders and their causes, as well as methods for diagnosing taste sensation abnormalities.

1. PHYSIOLOGY
OF
TASTE SENSATION
PRESENTED BY
N.NARMATHA

2. INTRODUCTION:
• Taste belongs to our chemical sensing system, or the chemosenses.
• The complex process of tasting begins when tiny molecules
released by substances stimulate special cells in the nose, mouth,
throat.
• Tongue is a muscular organ situated in the floor of the mouth.
• Associated with functions of taste, speech, mastication and
deglutition.

3. • Taste buds – sense organs for taste or gustatory sensation.
• One’s sense of smell also contributes strongly to taste sensation
Women have better sense of taste – typically have more taste areas –
fungiform papillae and taste buds than men.

4. ANATOMY:
Tongue has
• Root
• Tip
• Body

6. PAPILLAE OF TONGUE:
• Gives characteristic roughness to
anterior two-thirds of tongue.
• Projections of mucous membrane or
corium.
• Taste buds are present
TASTE BUDS:
Ovoid bodies - 50 – 70 µ

7. TYPES OF PAPILLAE:
• Vallate or circumvallate papillae
• Fungiform papillae
• Filliform papillae or conical papillae
• Foliate papillae

8. VALLATE PAPILLAE:
Diameter: 1-2 mm
No: 8 - 12
Situation: in front of sulcus terminalis.

9. FUNGIFORM PAPILLAE:
• Colour: Bright red
• Numerous near tip and margins of tongue.
• Scattered over the dorsum.
• Size: < vallate papillae > filliform papillae

10. FILLIFORM PAPILLAE:
Colour:Velvet
Situation: presulcal area of dorsum of tongue
Smallest and most numerous.

11. FOLIATE PAPILLAE:
Situation :In front of the palatoglossal arch.

12. STRUCTURE OF TASTE BUD

13. MUSCLES OF TONGUE

15. ARTERIAL SUPPLY OF TONGUE:
Lingual artery , tonsillar , ascending pharyngeal branch of external
carotid artery.

16. VENOUS DRAINAGE

17. LYMPHATIC DRAINAGE

18. NERVE SUPPLY

19. PRIMARY SENSATIONS:
• Sour taste
• Salt taste
• Sweet taste
• Bitter taste
• Umami taste

20. GUSTATORY PATHWAY

22. Sour taste: Caused by acids - hydrogen ion concentration
Salty taste: Elicited by ionized salts – sodium ion concentration.
Sweet taste: Organic chemicals, sugars, glycols, amino acids etc..
Bitter taste: Organic substances containing nitrogen, alkaloids.
Umami: pleasant taste sensation that is quantitavely different from
sour, salt , sweet or bitter.

26. MECHANISM OF STIMULATION:
Binding of taste
chemical to protein
receptor molecule
Opens ions channels
Allows positively
charged sodium ions
or hydrogen ions
depolarize
Taste chemical
washed away
Stimulus removed.

28. GENERATION OF NERVE IMPULSES:
• First application of stimulus: rate of discharge – rises to peak in a
small fraction of second
• Next few seconds : back to lower ,steady level

29. GENERATION OF NERVE IMPULSES

30. PATHWAY FOR TASTE:
• RECEPTORS:
• Type III cells of taste buds.
• Each taste bud is innervated by about 50 sensory nerves .
• Each nerve fiber supplies atleast 5 taste buds.

31. FIRST ORDER NEURONS:
• Present in the nuclei of different cranial nerves.
• Dendrites of the neurons are distributed to the taste buds.
Fibres run along the following nerves.
1. Chorda tympani – anterior two thirds of tongue.
2. Glossopharyngeal nerve fibres – posterior one- third .
3. Vagal fibres – taste buds in other regions.
• Axons of first order neurons run together in medulla oblongata and
terminate in the nucleus of tractus solitarius.

32. Second order neurons:
• Present in the nucleus of tractus
solitarius.
• Axons run through medial
lemniscus and terminate in
posteroventral nucleus of
thalamus.
Third order neurons:
• Center – opercular insular cortex
in parietal lobe of cerebral
cortex.

33. Taste receptors
Chemical energy
Action potential in
nerve fiber
TASTE TRANSDUCTION:

34. receptors
Stimulated by substances
dissolved in mouth by saliva
microvilli
Receptor potential
Action potential

35. APPLIED PHYSIOLOGY:
1.Ageusia – Loss of taste sensation .
Cause:
• Tissue damage to nerves – chorda tympani nerve,
glossopharyngeal nerve.
• Lingual nerve damage during otologic surgery.
• Neurological disorders,
• Drugs – cisplastin, ACE inhibitors, azelastin,clarithromycin.

36. 2.Hypogeusia – diminished taste sensation.
Cause:
• Drug – bleomycin
• Zinc defeciency.

37. 3.Hyperguesia: enhanced gustatory sensitivity.
- malfunction in the signal propagation from tongue to brain
4.Dysgeusia/paraguesia – altered taste sensation.
Cause :
Drugs
Zinc defeciency.

38. 5.Cacoguesia – bad taste in the mouth.
- occurs independent of any drug, food, liquid
- described as all five taste signals, permanently on and mixing.
6.Heteroguesia –inability to distinguish between tastes.
- lingual or glossopharyngeal nerve sheaths damaged – signal
contamination between strands.
-Damage to olfactory centre in brain.

39. 7.Phantoguesia – gustatory hallucination
- due to misfiring nerves – sends signals where there is
no source
- linked to memory in the brain
8.Norguesia –the sought after ideal.

40. • Familial dysautonomia – loss of taste sensation.
• Taste blindness – Very high threshold to bitter taste

41. CAUSES:
Defeciency
• Vitamin B 12 defeciency
• Zinc responsible for
• repair and produce taste buds
• Cofactor for alkaline phosphatase
(enzyme in taste bud membranes)

42. ENDOCRINE DISORDERS:
• Cushing’s syndrome
• Hypothyroidism - has effects at multiple points of the gustatory and
olfactory perceptual pathways.
• Diabetes mellitus
- Oral & perioral disorders(hypogeusia)
- Xerostomia
- Glossitis – ageusia.
- Diabetic autonomic neuropathy(rare-0.05%)
- Peripheral neuropathy.
- Sweet taste receptors(T1R2) increased.
- Metformin,glibenclamide

43. LOCAL INJURY OR INFLAMMATION:
• Radiation therapy saliva interacts & protects taste receptors
decrease in saliva
mediates sour & sweet taste
(bicarbonate ions,glutamate)
dysguesia
• Glossitis
• Tobacco usage
• Denture use

44. MEDICATIONS:
• Mechanism:
Oral mucositis, oral infection, salivary gland dysfunction.
• Antiproliferative drugs - cisplastin
inhibition of sodium channels
• ACE inhibitors – losartan
• The ACE enzyme is a zinc-dependent enzyme.
• ACE inhibitors, need zinc for reaction,
• the inhibition of ACE by the drug - affect the zinc of the ACE
protein in the salivary gland cells - alter taste

45. • Antihistamines – azelastine,emedastine
• Drugs containing sulfhydryl groups – penicilamine, captopril
React with zinc - defeciency - dysguesia

46. • Anti rheumatic drugs
• Metronidazole ,chlorhexidine
interact with metal ions in cell membrane.
• Calcium channel blocker -Amlodipine
block calcium sensitive taste buds.

47. NEUROLOGIC CONDITIONS:
• Bells palsy
- facial nerve damage - aguesia
• Familial dysautonomia
• Multiple sclerosis

48. Others :
• Ageing – diminished taste buds.
• Xerostomia
• Injury to glossopharyngeal nerve
• Damage to pons,thalamus,midbrain
• Anxiety disorder
• Cancer
• Renal failure
• Hepatic failure
• Bladder obstruction – dysguesia
areas responsible for urinary system and taste are in close
proximity(pons &cerebral cortex).

49. • Upper respiratory and middle ear infections
• Cold – odors – cant reach sensory cells in the nose -food
tends to taste bland .
• Sinus infections
• Surgery to ear ,nose,throat
• Poor oral hygiene
• Third molar extraction.

50. Diagnosis of taste sensation:
Chemical methods:
• Determined by measuring the lowest
concentration of a taste quality
• Asked to compare the tastes of different substances
• To note how intensity of a taste grows when substance’s
concentration is increased.
• Semi-quantitative clinical gustometry using a filter-paper disc
recognition thresholds for four basic tastes (sweet, salty, sour
and bitter) were evaluated using chemical solutions (sucrose,
NaCl, tartaric acid and quinine, respectively).

51. Electrogustometry:
Measures minimum amount of current
required to excite sensation of taste.
Method:
• Small current applied to lateral border of
tongue(−8 dB)
• Current slowly increased until patient a
ble to perceive the mettalic taste.
• Normal threshold:1mA
• 4mA in chorda tympani involvement.

52. References:
• Grey,s anatomy,
• B.D .chaurashia
• Orban,s
• Textbook of physiology – guyton
• Sensory malfunction : taste
• Appleyard D.A cold left me unable to smell or taste for two
years, 29 january 2012.
• mandibular nerve involvement in diabetic polyneuropathy
mucle nerve 1998:21(12):1673-9

53. Thank you