Physiology of taste

Physiology of taste and taste buds ppt

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

5. 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

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

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

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

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

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

11. STRUCTURE OF TASTE BUD

12. MUSCLES OF TONGUE

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

14. VENOUS DRAINAGE

15. LYMPHATIC DRAINAGE

16. NERVE SUPPLY

17. PRIMARY SENSATIONS: Sour taste Salt taste Sweet taste Bitter taste Umami taste

18. GUSTATORY PATHWAY

19. 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.

20. MECHANISM OF STIMULATION:

21. 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

22. GENERATION OF NERVE IMPULSES

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

24. 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. Chorda tympani – anterior two thirds of tongue. Glossopharyngeal nerve fibres – posterior one- third . 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 .

25. Second order neurons: Present in the n ucleus 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.

26. TASTE TRANSDUCTION:

27. receptors Stimulated by substances dissolved in mouth by saliva microvilli

28. 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 .

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

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

31. 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.

32. 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 .

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

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

35. 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

36. 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

37. 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

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

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

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

41. 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).

42. 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.

43. 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). 

44. 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.

45. 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

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