Taste pathway

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 TASTE Concentration of H+ ions Intensity α log of H+ ion More acidic α more sour

6. SALTY TASTE Elicited by ionized salts Sodium ion concentration

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

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

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

10. THRESHOLD FOR TASTE

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

12. 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

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

14. 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

15. LOCATION OF TASTE BUDS

16. FILIFORM PAPILLAE

17. FUNGIFORM PAPILLAE

18. CIRCUMVALATE PAPILLAE

19. FOLIATE PAPILLAE

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

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

22. CENTRAL TASTE PATHWAY

23. 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

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

25. 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

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

27. 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

28. 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

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

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

31. 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

32. 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

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

34. 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

35. 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.

36. 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

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

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

39. 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