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: