Taste.pdf

CHEMICAL SENSES: TASTE Mohamed Hassan, CAND PhD  Taste Taste (gustation) and smell (olfaction) are classified as visceral senses Physiologically, they are closely related to each other Taste receptors are chemoreceptors Taste recepto...

CHEMICAL SENSES: TASTE Mohamed Hassan, CAND PhD  Taste Taste (gustation) and smell (olfaction) are classified as visceral senses Physiologically, they are closely related to each other Taste receptors are chemoreceptors Taste receptors are exteroceptors Dissolved chemical molecules in saliva stimulate receptors  Taste Taste and smell sensetions allow individuals to distinguish between estimates of up to 30 million compounds Stimulation of the taste or smell receptors induces pleasurable or objectionable sensations: to seek: a nutritionally useful, good–tasting food to avoid: a potentially toxic, bad-tasting substance  Chemical receptors in the taste cell Scientific studies have shown at least 13 probable chemical receptors: 2 sodium 2 potassium 2 sweet 2 bitter 1 chloride 1 adenosine 1 inosine 1 glutamate 1 hydrogen ion receptor  Primary sensations of Taste Primary sensations of taste have been grouped into five general categories :  Taste Substances SOUR SALTY SWEET BITTER H+ ion(acides) Ionized salts Sugars 1. Long- chain HCl NaCl Glycoles organic Formic Acid CaCl2 Alcohols substances that Chlooracetate NaBr Aldehides contain nitrogen Acetyllactic acid NaI Ketons 2. Alkaloids Lactic acid LiCl Amids Quinine Tartaric acid NH4Cl Esters Caffeine Malic asid KCl Amino acids Strychnine K+-H+ tartar Lyzyltaurin Small proteins Nicotine Acetic acid Ornithyltaurin Sulphonic acids Morphine Citric acid Halojenic acids Cocaine Carbonic acid Chloroform Atropine Inorganic salts of Pb and Be Stimulation of the taste receptor Transient receptor potential cation channels (TRP)  Sour Taste The sour taste is caused by acids (protons =H+ ions) The sour taste is triggered by the Epithelial sodium channels (ENaC) that allow to entering the proton into the cytoplasma  Salty Taste -1 Salty taste is mediated by Na+ influx through amiloride-sensitive Na+ channels Main receptor is epithelial sodium channel (ENaC). - ENaC receptors in the mouth and other part of the body are inhibited by the AMILORIDE.  Salty Taste-2 ENaC inhibition by the amiloride on the tongue is not full It has been thought presence of other salt receptors on the taste buds Na+ influx into the salt receptors causes depolarization and release glutamate as a transmitter. Glutamate depolarizes afferent neurones  Bitter Taste Different compounds cause bitter taste Most of these compounds are poisons Bitter taste is associted with gustducin (a heterotrimeric G protein) receptor At least, in human, there are 24 different bitter receptors associated with G protein  Bitter taste receptors (G protein) Gustducin Phospholipase C (PLC) the release of Ca2+ from intracellular stores Inositol triphosphate (IP3) and Diacylglycerol (DAG) Ca++ Quinine may depolarize taste cells by blocking apical K+ channels  Sweet Taste Sweet tastant G protein Adenylyl cyclase (gustducin) IP3 ATP cAMP PKA PKA phospohrilates K+ channels K+ channel conductance (basolateral membrane) Depolarization  Umami (=delicious)Taste Umami taste , which was first identified and named by a Japanese researcher, is triggered by amino acids. This taste mediates to glutamate and monosodium glutamate in Asian dishes This taste occurs via activation of the metabolic glutamate receptors (mGluR4) in taste buds  Treshold for the stimulation Sour 0.0009 N HCl Salty 0.01 M NaCl Sweet 0.01 M Sucrose Bitter 0.000008 M Quinine  Taste Buds Diameter of 1/30 mm, the lenght of 1/16 mm. Composed of 50-100 modified epithelial cell (taste and supporting) Mature cells located in the center. Life span is about 10 days in lower mammals but is unknown for humans Microvilli provide receptor surface for taste Adults have 3 000-10 000 taste buds on the surface of the tongue About 1000 taste buds are in the roof of the mouth and wall of the throat  Location of the Taste buds Taste buds: A large number of taste buds are located on the circumvallate papillae (V line on the surface of posterior tongue)( about 100 buds/each papillae, in edge of the bud) Moderate numbers are on the fungiform papill (about 5 buds/papilla, top side) Moderate numbers are on the foliat papilla There is no taste bud on the Filiform papilla. Taste buds are also located on the palate, and a few are on the tonsillar pillars, on the epiglottis, even in the proximal esophagus.  The distribution of the different tastes on the tongue Salty and Sweet buds are located on the tip of the tongue , Sour buds are located on the lateral edges of tongue, Bitter buds are located on the root of tongue and soft palate  Transmission of the Taste Signals Signals from the anterior two thirds of the tongue pass first into the lingual nerve (V), then through the chorda tympany (branch of the nerve VII) into the facial nerve , and finally into the nucleus tractus solitarius (NTS) Signals from the circumvallate papillae on the back of the tongue and from other posterior region of the mouth and throat are transmitted through the glossopharyngeal nerve also into the NTS. Finally signals from the base of the tongue and from the other parts of the pharyngeal region are transmitted into the NTS by way of the Vagus nerve Signals from the NTS pass to Ventral posterior nucleus of the thalamus and then pass to the Gustatory cortex Taste Reflexes: From the NTS, many taste signals are transmitted to the süperior and inferior salivatory nuclei. These nuclei transmit signals to the submandibular, sublingual ve parotid glands to control of the saliva secretion during the ingestion and digestion of food. Taste sensations show fast adaptation (within one minute)