TASTE (GUSTATION)kityamuwesi

OUTLINEReview h/o taste bud as sensor cellsClassification of taste substance areasGeneration of taste electrical signalsTransmission of signals to cerebral cortical cells responsible for tasteInterpretation of tasteTaste function testsPathophysiology of taste

IntroductionTaste is a form of direct chemoreceptionIt allows descrimination between desirable & undesirable substances In humans and many other vertebrate animals the sense of taste partners with the less direct sense of smellThey allow recognition of proximity of other animals or individuals within the group

Introduction cont.

Taste and smell are tied to primitive emotional and behavioral functions of the nervous system

HistoryIn Western culture, the concept of basic tastes can be traced back at least to Aristotle, who cited two basic tastes:SucculentSweet & bitterHarshSalt & pungentSour (Elaboration of the basic two)Puckery

History cont.The ancient Chinese Five Elements philosophy lists slightly different five basic tastes:Bitter, salty, sour, sweet and spicy

Japanese and Indian cultures each add their own sixth taste to the basic five.

Sense of tasteMainly a function of taste buds but influenced by:Olfactory systemSomatosensory systemImportance Of TasteSelection of food according to:DesireMetabolic need

Taste BudsAre taste receptorsOvoid bodies of about 50-70 mEach taste bud is made up of 4 types of cells:Basal cellsType I cellsType II cellsType III cells (Gustatory cells)Substentacular cells

Locations Of Taste BudsWall of troughs surrounding circumvallate papillae (V-line)Fungiform pupillaeFoliate papillae (Folds lat. Surf. Tongue)PalateTonsillar pillarsEpiglottisUpper oesophagus

Some Lingual Papillae

Each taste bud is innervated by about 50 nervesEach nerve fiber receive input from about 5 taste buds

The back of the tongue: bitter The sides of the tongue near the back: sour The sides of the tongue near the front: salty The tip of the tongue: sweet Taste Map

Primary SensationOver 13 groups of chemicals have been identified to excite taste receptors but so far they have been grouped into 5 basic tastes:SourSaltySweetBitterUmami

SaltinessSaltiness is a taste produced primarily by the presence of sodium ions Other ions of the alkali metals group also taste saltyHowever the further from sodium the less salty is the sensationThe size of lithium and potassium ions most closely resemble those of sodium and thus the saltiness is most similarIn contrast rubidium and cesium ions are far larger so their salty taste differs accordinglyPotassium, as potassium chloride is the principal ingredient in salt substitutes

SourSourness is the taste that detects acidityThe mechanism for detecting sour taste is similar to that which detects salt tasteHydrogen ion channels detect the concentration of hydronium ions (H3O+ ions) that are formed from acids and water

SweetnessProduced by Sugars, some amino acid & protein, aldehydes and ketones, which contain a carbonyl groupSweetness is detected by a variety of G protein coupled receptors

Sweetness cont.The compounds which the brain senses as sweet are those compounds that can bind with varying bond strength to two different sweetness receptors. These receptors are T1R2+3 (heterodimer) and T1R3 (homodimer)BitternessThe TAS2Rs (taste receptors, type 2, also known as T2Rs) such as TAS2R38 coupled to the G protein gustducin are responsible for the human ability to taste bitter substances

UmamiUmami is the name for the taste sensation produced by compounds such as glutamate, and are commonly found in fermented and aged foods. In English, it is also described as "meatiness", "relish" or savoriness Taste of MSGSpecialized metabotropic glutamate receptor may be responsible

Taste/GustationGustatory pathwayInfo from anterior tongue travels through chorda tympani, a branch of the facial (7th) nerve; info from posterior tongue travels through lingual branch of 9th CN; 10th CN carries info from palate and epiglottisFirst relay station is the nucleus of the solitary tract (NTS), in the medulla, which then projects to the thalamus, then to the primary gustatory cortex, located at base of frontal cortex and in the insular cortex

Other Sensations (Somatosesory)Fattiness DrynessMetallicnessPrickliness or hotnessCoolnessNumbnessHeartiness (Kokumi)Temperature

DrynessUnripe fruits, contain tannins or calcium oxalate that cause an astringent or rough sensation of the mucous membrane of the mouth or the teeth. Prickliness or hotnessSubstances such as ethanol and capsaicinExcite both normal and tatse reception & trigeminal nerve receptor with (TRPV1)CoolnessSpearmint, menthol, ethanol or camphor Activate cold trigeminal receptors TRP-M8 ion channel

Taste AbnormalitiesAgeusiaHpogeusiaDysgeusia

Many factors affect taste perception, including:Aging Color/vision impairments Hormonal influences Genetic variations; (Phenylthiocarbamide)Oral temperature Drugs and chemicals Natural Substances (Miracle fruit) CNS Tumors (esp. Temporal lobe lesions) and other neurological causes Plugged noses Zinc deficiency

Taste Function TestsNo reliable method has been reportedSome methods being tried include:Sip and SpitTaste stripsGustrometry

The End Thanks

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