physiology of taste sensation

physiology of

“ taste sensation / Gustation ”

Presented

By

Sahithi

TUTOR( M.SC PHYSIOLOGY)

Introduction

Taste allows the person to select desirable food depending upon their metabolic needs and it also avoids

the person to separate from undesirable, Lethal food.

Anatomy of Tongue

TONGUE Tongue is the main site of taste detection.On the dorsal surface of tongue, the mucous membrane is having many PAPILLAE.

Papillae are 4 types : Circumvallate Papillae, Fungiform Papillae ,

Foliate Papillae , Filliform Papillae

Walls of papillae contains Taste buds.

TONGUE With Taste Bud

• Taste is a visceral sensation associated with digestive system.

• Taste receptors are chemical receptors.

Distribution of Taste Buds

Palate Epiglottis Tongue Pharynx Upper Esophagus.

CIRCUMVALLATE PAPILLAE: o ‘V’ shaped groove anterior and posterior parts of tongue.

o Contain 100 – 200 no of taste buds .FUNGIFORM PAPILLAE:o Red , flat dot structures.o Contain 5 – 10 taste buds.

FOLIATE PAPILLAE:o Transverse mucosal folds on postero lateral surface of tongue.o Contain few taste buds.

FILLIFORM PAPILLAE:o Conical projections .o Do not contain taste buds .

TASTE BUD

Structure of Taste Bud • SHAPE : Barrel / ovoid.• LENGTH : 50 - 70 µm.

Total no. of Taste buds in Humans : 1,00,000.– In Adults : 3,000-10,000.– In Children : Few more than Adults.– After the age of 45 years the Taste buds are degenerate. So “Hypoguesia” is common in

Old age.• LIFE SPAN : 10 days .

Old taste buds are replaced by new cells by the process of Mitosis. Basal cells arise from Epithelial cells differentiate into new Taste buds.

• STRUCTURE : taste bud consist of1. Basal Cells 2. Sustentacular Cells.3. Gustatory Receptor Cells.

All the cells are connected with each other at their neck region. Through the taste pore the taste cells are exposed to the saliva of oral cavity.

• NERVE SUPPLY: Each taste bud is innervated by 50 nerve fibers.

TASTE BUD - Sense Organ of Taste

Type of Tastes

SweetBITTER

Taste Modality

Umami• It is a Japanese word means “Delicious”.• First proposed by prof.“Kikunae Ikeda” of The Tokyo

Imperial University in 1908.• It is extensively found in Asian recipes. Notably in

Fish, Shell Fish, Cured Meats, Vegetables like Chinese Cabbage, Spinach etc.

• It is recently added taste in Taste classification.• Umami stimulates Metabotopic Glutamate receptors.

Salt Sensation

• Nacl Stimulates ENaC receptors leads to their depolarization. The depolarized receptors stimulates sensory nerve fiber by releasing glutamate.

• Taste Threshold = 0.01M.

Sour Sensation

• Protons and Acids present in Sour food compounds depolarize Taste cells by stimulating ENaCs and HCN receptors.

• Taste Threshold = 100M.

Bitter Sensation

• Poisons, Lethal compounds, Alkaloids depolarize the Taste cells by binding with G-protein called Gustuducin and also blocking Apical K+ Channel.

• Taste Threshold = 0.000008M

Sweet Sensation

• sweet components like Sugars, Glycols, Alcohols, Aldehydes & Esters depolarize the taste cells by binding with G-protein called as Gustuducin.

• Taste Threshold = 0.01M.

Taste Pathway

• Anterior 2/3rd of tongue is supplied by a branch of “Facial Nerve” called “Chorda Tymphani”.

• Posterior 1/3rd of tongue is supplied by “Glossopharyngeal Nerve”.

• Taste buds located on other parts of the tongue are supplied by “Vagus Nerve”.

Taste senses stimulates the Taste buds

Sensory nerve fibers carrying taste sensation from taste buds travel through VII, IX & X Cranial Nerves to reach Brain Stem.

Taste Fibers (First order Neurons) in these Three Cranial Nerves are Myelinated but conduction velocity is slow. They join in “Nucleus Tractus Solitarius” in Medulla

Oblongata of Brain Stem.

The Axons (Second order Neurons) arise from “Nucleus Tractus Solitarius” ascend in Ipsilateral side to Terminate on “Ventral Postero Medial Nucleus of

Thalamus”.

From the Thalamus the Third order Neurons arise and pass in Thalamic Radiation to terminate in “Insular cortex”.

Insular cortex is the higher center for Concious perception of taste and discrimination

Taste Abnormalities

AGUESIA – Absence of Taste sensation

Causes :

damage to VII, IX & X Cranial Nerves

Drugs – “contain Sulphydryl group”.

Familial Dysautonomia.

HYPOGUESIA – Decreased Taste sensation

DYSGUESIA – Disturbed Taste sensation.

Causes :

Temporal Lobe Syndrome

Acknowledge

• In my view it’s a plat form to express my sincere thanks to my professors for their valuable teaching , encouragement & guidance throughout my studies.

• Dr . N . Mallikarjun Reddy MD (HOD),

• Dr .Sharan B Singh MD ( PROFESSOR).