NPB+112+11+Taste+lecture+Notes

NPB+112+11+Taste+lecture+Notes - NPB 112 Winter 2011 3/3...

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1 NPB 112, Winter 2011: 3/3-3/8/11 Taste, Ch. 15 I. Concepts of taste A. nonvolatile, water-soluble molecules B. thresholds relatively high for most tastants: mM range 1. however, bitter is detected in very low ( μ M) range because poisonous plant alkaloids are bitter (defense mechanism to prevent ingestion). 2. sweet is detected at high concentrations-signals caloric value of food. 3. Don’t waste time eating food of low caloric content C. Basic tastes-poor linguistic descriptors limit how we classify tastants. 1. Aristotle: 7 basic tastes (sweet, sour, salty, bitter, harsh, pungent, astringent) 2. Henning: taste tetrahedron (sweet, salty, sour, bitter) 3. Tongue taste map: Misconception: tip=sweet, sides=sour and salty. Not true, the tongue can detect all tastes across entire surface, however, there is regional sensitivity to particular taste qualities. Fig. 15.16 (B) II. Anatomy A. Taste organs (tongue, pharynx, palate, epiglottis) 1. Tongue (Fig. 15.16 a) i. Papillae: 4 types -filliform (non-gustatory; hold food, bolus formation) -fungiform (mushroom shaped; most abundant) -foliate (ridges on back/side) -circumvallate (in trenches in back of tongue: Fig. 15.16 A) ii. Each papilla contains 1~300 taste buds B. Taste buds (Fig. 15.17 A)-Barrel shaped-found in papillae: contain 4 cell types 1. taste receptor cells; molecular tastant receptors expressed in microvilli which project into taste pore (site of signal transduction: Fig. 15.17 B) *a given taste receptor cell expresses only ONE type of molecular tastant receptor 2. basal cells-generate new taste receptor cells
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2 3. support cells-support 4. gustatory afferent fibers form synapse with “presynaptic” taste receptor cells (see below) C. Taste nerves (Fig. 15.15 A) 1. chorda tympani (branch of cranial nerve VII) innervates the anterior 2/3 of tongue (primary gustatory neurons) 2. glossopharyngeal nerve (cranial nerve IX) innervates posterior 1/3 of tongue 3. vagus nerve (cranial nerve X) innervates pharynx, palate, and epiglottis D. Tongue map: ALL areas of tongue can detect sweet, sour, salty, butter and umami taste qualities; it’s just a matter of degree. 1. back of tongue: more sensitive to bitter (glossophyrangeal nerve) 2. front of tongue: mores sensitive to sweet and umami (chorda tympani) 3. Sides and front: sensitive to salty 4. throat: more sensitive to salty and sour III. Taste Transduction A. Overview
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