TASTE PATHWAY

CONTENTS• INTRODUCTION• PRIMARY TASTE SENSATION• TASTE BUDS• PAPILLAE OF TONGUE• TASTE PATHWAYS• APPLIED ASPECTS• CLINICAL CONSIDERATIONS• CONCLUSION• REFERENCES

INTRODUCTION•Sense of taste-allow us to separate

undesirable or even lethal foods from those that are pleasant to eat.

•Function of taste buds

•Taste stimulate secretion of saliva and gastric juices.

•Allows to select food

Primary sensations of taste

2 Sodium Receptor

2 Potassium Receptor

1 Chloride Receptor

1 Adenosine Receptor

1 Inosine Receptor

2 Sweet Receptors

2 Bitter Receptors

1 Gluatamate Receptor

1 Hydrogen Ion Receptor

SOUR

SWEET

BITTER

SALTY

UMAMI

SOUR TASTE

Concentration of H+ ions

Intensity α log of H+ ion

More acidic α more sour

SALTY TASTE

Elicited by ionized salts

Sodium ion concentration

SWEET TASTE• Sugars

• Glycols

• Alcohols

• Aldehydes

• Ketones

• Inorganic salts of lead & beryllium

•Amides

•Esters

• Aminoacids

•Small proteins

•Sulfonated acids

BITTER TASTE

Long chain organic substances – nitrogen

Alkaloids – drugs-quinine,caffeine

Deadly toxins found in poisonous plants

Rejection of food

UMAMI TASTE

Japanese word- ‘pleasant sevory taste’

Glutamate receptor

Kikunae Ikeda in 1908

Fish, mushrooms,aging cheese, spinach, ripe tomatoes,meat extracts.

THRESHOLD FOR TASTE

• Sour taste• HCl

0.0009N

TASTE BUD•Goblet shaped

•Diameter : 1/30 mm

•Length : 1/16mm

•50 modified epithelial cells

Supporting cells Gustatory cells

• Appears early – 7 to 8 weeks of IUL

• Matures later after gestation

• Increase in number after birth

• Adults- 3000-10,000

• Children

• >45yrs

• Ability to Regenerate – gustatory nerve Degenerate ---taste sensation

TASTE CELLS

•Mitotic division

•Mature cells- lie toward centre of the bud-break up & dissolve

•Life span- 10 days

HISTOLOGY OF TASTE BUD •Type 1 – long and narrow ,dark

cells,irregular nucleus

•Type II – long, light cells, round oval nuclei

•Type III – similar to type II , dense cored vesicle in basal portion

•Type IV - contacts basement membrane,doesnot extend to the taste pore - basal cell

LOCATION OF TASTE BUDS

FILIFORM PAPILLAE

FUNGIFORM PAPILLAE

CIRCUMVALATE PAPILLAE

FOLIATE PAPILLAE

MECHANISM OF TASTE SENSATION

Taste cell membrane- - - - - -

+ + + + + +

Taste substance

Depolarization

Receptor potential

•Generation of nerve impulses – strong immediate signal

Weaker continuous signal

Exposed to stimulus

CENTRAL TASTE PATHWAY

Central Termination – Afferent Fibers

•Facial (VII) nerve- chorda tympani – entirely gustatory

•Glossopharyngeal ( IX ) – gustatory & somato sensory fibres

•Vagus (X ) – superior laryngeal nerve –gustatory & chemosensory fibres

NTS

ROSTARL ZONE –

gustatory information

CAUDAL – swallowing, respiartion,

gastric motility

MEDIAL LATERAL

•Three main types of neurons

•ELONGATE: fusiform cell body, 2 primary dendrites

•MULTIPOLAR: stellate , pyramidal soma ,3-4 primary dendrites

•OVOID : small soma, 3 or more primary dendrites

PONTINE TASTE RELAY

•Ascending axons bypasses – ventroposteromedial nucleus of thalamus.

•Organised along dorsoventral axis

•Response characteristics - NTS

THALAMUS AND CORTEX• Thalamic gustatory relay nucleus

ventro medial tip

ventro postero medial thalamic nucleus

part of ventro basal complex

• Projections further ascend – agranular insular cortex

• Gustatory stimulation – cortical gustatory projection

ROLE OF SALIVA • Essential for normal taste function

• Dry mouth- difficult to taste

• Acts as a solvent

• Fungiform – saliva from all salivary glands

• Remaining papillae – von Ebner’s

• Taste buds –palate,larynx,pharynx- minor salivary glands

•Feeding/drinking

Muscles move food around mouth

Facilitates access of solubilzed taste stimuli entirely

•Significant – clefts of vallate & foliate papilla

Effect of reduced salivation

•Head and Neck radiation – taste disturbances

•Affect turn over of taste buds

•Damage nerve terminals

•xerostomia- altered taste perception

Salivary gland removal

Electronmicroscopy of taste buds

macrophages, large number of bacteria

altered taste perception

•Sjogren syndrome- reduced taste sensitivity for all 4 taste qualities

CLINICAL CONSIDERATIONS• Complete loss – aguesia

• Partial loss – hypoguesia

• Distortions of taste – dysguesia

• Abberant taste - Abnormal stimulation – Phantom – chemosensory disorders

• Vitamin A deficiency - keratinization

• Gustatory hallucinations -epilepsy

•Familial dysautonomia – smooth tongue + papillae taste buds

•Malignancy – anorexia

•Burning mouth syndrome

•Taste blindness- genetic - recognize taste

•Poor oral hygiene

Incidence of taste disturbance with common medications

Medication Incidence , %

•Acetazolamide 12-100•Captopril 2-7•Lithium 5•Procainamide 3-4•Amiodarone 1-3

Rebecca Douglass et al, Drug-related taste disturbance A contributing factor in geriatric syndromes; Can Fam Physician 2010;56:1142-7

INVESTIGATIONPossible causes

•Detailed history and examination - local causes.

•Haematological and biochemical investigations - nutritional and endocrine causes

•Computed tomography - neurological causes

•Ageing processJ M Boyce, G R Shone, Effects of ageing on smell and taste; Postgrad Med J 2006; 82:239–241.

MANAGEMENT

•Counselling and reassurance

•Relatives or neighbours need closer involvement to check for spoiled food that if eaten could lead to food poisoning.

•Flavour enhancement - salt

J M Boyce, G R Shone, Effects of ageing on smell and taste; Postgrad Med J 2006; 82:239–241

CONCLUSION

•Taste sensation allow us to separate lethal foods

•5 principal taste

•Mainly in taste buds

•Lack-anorexia, weight loss.

REFERENCES

•Bradley RM: Essentials of Oral Physiology, USA,1998, Mosby

•Antonio Nanci. Salivary Glands. Tencate’s Oral Histology 7th ed.Mosby .India. 2008

•G S Kumar.Salivary glands .Orban’s Oral Histology and Embryology.12th ed.Elsevier India;2007

•Arthur Guyton.The Chemical senses. Textbook of medical physiology.10th ed WB Saunders;2001

•J M Boyce, G R Shone, Effects of ageing on smell and taste; Postgrad Med J 2006;82:239–241.

•Rebecca Douglass et al, Drug-related taste disturbance A contributing factor in geriatric syndromes; Can Fam Physician 2010;56:1142-7