Sensation of Taste 1432

2. Sensation of Taste1432 Professor A.M.A Abdel Gader MD, PhD, FRCP (Lond., Edin), FRSH (London) Professor of Physiology, College of Medicine & King Khalid University Hospital Riyadh, Saudi Arabia

4. Chemical Senses • TASTE • SMELL Both determine the flavour of food Taste and smell are closely linked even though they involve different receptors and receptive processes. This suggests an overlap in central processing.

5. Anatomy of Taste Sensation

6. Taste Buds

7. Sensation of Taste – cont. Receptors: • Located in taste buds in: • Tongue • Epiglottis • Soft Palate • Pharynx

8. Anatomy of Taste Buds • 10,000 taste buds found on tongue, soft palate & larynx • Taste buds consist of: • ~50 receptor cells surrounded by supporting cells • Gustatoryhairs project through the taste pore • Life span of 10 days • Basal cells develop into supporting cells then receptor cells

9. Organized like a bunch of bananas

11. Taste Buds

12. There are about 4500 taste buds per average tongue

13. Nerve supply of tongue • Fibres from: • Epiglottis • Palate • Pharynx • VAGUS

14. Frontal Operculum Vagus Nerve Mouth & Larynx Insular Cortex Tongue Glossopharyngeal Nerve Nucleus Solitary Tract (NST) Chorda Tympani Nerve Gustatory System Thalamus ML

15. Neuroanatomy Of The Taste System

16. Taste information is send to the CNS by the nerve #7, 9 and 10 to the taste nucleus (n. solitarius); from there to thalamus and insular cortex

17. Physiology of Taste

18. Sensation of Taste – cont. Physiology of Taste: Dissolution in Saliva Attachment to Receptors Generator Potential Action Potential

19. Sensation of Taste –Physiology of Taste – cont: Primary modalities of taste: • Sour • Salt • Sweet • Bitter • umami (deliciousness), a taste associated with glutamate & other nucleotides has receptors located at the back of the pharynx.

20. Sensation of Taste –Physiology of Taste – cont:Primary modalities of taste: • Sour • Salt • Sweet • Bitter Evidence for 4 modalities???

21. Sensation of Taste –Physiology of Taste – cont:Primary modalities of taste: Sensitivity differs in different areas, but all tastes can be perceived at most areas of the tongue

22. Sensation of Taste –Physiology of Taste – cont:Primary modalities of taste: Sour, Salt, Sweet, Bitter Evidence for 4 modalities: • Cocaine on the tongue: Sensations disappear in the following order Pain sweet sour bitter salt touch

23. Sensation of Taste –Physiology of Taste – cont:Primary modalities of taste: Sour, Salt, Sweet, Bitter Evidence for 4 modalities: • Gymnemic acid on tongue: • Bitter & sweet ……..disappear • Sour & salt ……………remain

24. Sensation of Taste –Physiology of Taste – cont:Chemical structure and taste: Threshold • Sour ... Acidity by {H+} – HCL ..pH = 3.5 • Salt … Sodium chloride ……….. 0.02 M • Sweet ..Sucrose ……………………… 0.01 M • Bitter .. Quinine Sulphate..0.000000M Artificial sweeteners: Saccharine, Cyclamates, Aspartame

25. Physiology of Taste – cont: Mechanism of stimulation of taste sensation: • Sour: Acids (H+) Blocks K+ channels • Salt taste Na+ Depolarization

26. Physiology of Taste – cont: Mechanism of stimulation of taste sensation: • Sweet G protein activation of adenyl cyclase c-AMP K conductance • Bitter G protein Activatn. of Phospholipase C IC-insitol (PO4)3 Ca2 release

27. Deep inside a ‘salty taste’ taste bud Sour is similar Electrical signal

28. Ion channels Saltiness or sodium receptors allow sodium ions to cross the membrane, thereby causing depolarization. Ionchannel Sourness receptors operate by closing potassium channels, which allows a positive charge to build up, thereby causing depolarization of the cell.

29. Mechanism of stimulation of taste sensation - cont: Saltiness and sourness are transduced directly by sodium and hydrogen ions respectively. The transduction process for sweetness and bitterness involve secondmessengers.

30. Sensation of Taste – cont. Discrimination of intensity of taste: • Poor (like smell) • Requires 30% change to allow discrimination of intensity

31. Sensation of Taste – cont. Adaptation to taste: Decreased sensation from repeated stimulus Entirely peripheral at the receptors

32. Clinical considerations • Ageusia: Absence of sense of taste • Dysgeusia: Disturbed sense of taste • Hypogeusia: Diminshed sense of taste • Hypergeusia: increased sense of taste

34. Thank you