Sensation of Taste

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.

Anatomy of Taste Sensation

Taste Buds

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

Anatomy of Taste Buds – cont. 10,000 taste buds found on tongue, soft palate & larynx Taste buds consist of: –~50 receptor cells (type 3) surrounded by supporting cells –Basal cells (type 1 &2) develop into supporting cells then receptor cells Gustatory hairs project through the taste pore Life span of 10 days

Papillae are found on the front, sides and back of the tongue. (The response is not as specific as indicated on the right). Anatomy of Taste Buds - cont

There are about 4500 taste buds per average tongue Each taste bud is innervated by 50 nerve fibers Each nerve fiber receives input from about 5 taste buds Anatomy of Taste Buds - cont

Fibres from: Epiglottis Palate Pharynx VAGUS Nerve supply of tongue

Mouth & Larynx Tongue Chorda Tympani Nerve Vagus Nerve Glossopharyngeal Nerve Nucleus Solitary Tract (NST) Thalamus Frontal Operculum Insular Cortex ML Taste Pathway

Taste information is send to the CNS by the crainial nerves # 7, 9 and 10 the taste nucleus (n. tractus solitarius) thalamus insular cortex Taste Pathway

Physiology of Taste

Dissolution in Saliva Attachment to Receptors Generator Potential Action Potential Physiology of Taste - cont

Sensitivity differs in different areas, but all tastes can be perceived at most areas of the tongue Its not this simple Physiology of Taste – cont: Primary modalities of taste:

Responses of Taste buds: Each taste bud responds strongly to one type of taste But they also respond to other tastes as well Physiology of Taste – cont: Primary modalities of taste:

Primary modalities of taste: –Sour –Salt –Sweet –Bitter Physiology of Taste - cont

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

Sour, Salt, Sweet, Bitter Evidence for 4 modalities: 1.Cocaine on the tongue: Sensations disappear in the following order Pain sweet sour bitter salt touch Physiology of Taste – cont: Primary modalities of taste:

Sour, Salt, Sweet, Bitter Evidence for 4 modalities: 2.Gymnemic acid on tongue: Bitter & sweet ……..disappear Sour & salt ……………remain Physiology of Taste – cont: Primary modalities of taste:

Threshold concentration. µmol/L –Sour... Acidity by {H + } – HCL –Salt … Sodium chloride ……………..… 2000 –Sweet..Sucrose ……………………………….. 10,000 glucose ……………………………….. 80,000 Saccharin ……………………………. 23 –Bitter.. Strychnine hydrochloride … 1.6 Quinine sulphate …………………….. 8 Artificial sweeteners: Aspartame, Cyclamate Sensation of Taste – Physiology of Taste – cont : Chemical structure and taste thresholds:

Mechanism of stimulation of taste sensation: –Sour: Acids (H + ) Blocks K + channels –Salt taste Na + Depolarization 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 (PO 4 ) 3 Ca 2 release Physiology of Taste – cont: