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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
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 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, BitterEvidence 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, BitterEvidence 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 .......... 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
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 tasteNa+
Depolarization
Physiology of Taste – cont:
Mechanism of stimulation of taste sensation:
–SweetG protein activation of adenyl
cyclase c-AMP K conductance
–BitterG protein Activatn. of
Phospholipase C IC-insitol (PO4)3 Ca2 release
Physiology of Taste – cont: