Sensation of Taste Chemical Senses TASTE SMELL Both

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

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

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

Anatomy of Taste Buds - cont 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

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

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

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

Taste Pathway

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

Physiology of Taste

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

Physiology of Taste – cont: Primary modalities of taste: I ts n o t th i s s im p l e Sensitivity differs in different areas, but all tastes can be perceived at most areas of the tongue

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: – Sour – Salt – Sweet – Bitter

Physiology of Taste – cont: Primary modalities of taste: – 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

Sensation of Taste – Physiology of Taste – cont: Chemical structure and taste thresholds: Threshold concentration. µmol/L – Sour. . . Acidity by {H+} – HCL. . 100 – 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

Physiology of Taste – cont: 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