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Special Senses: Smell & Taste

Special Senses: Smell & Taste. The Chemical Senses. The Chemical Senses. Primitive senses to alert us to savor or avoid substances Chemoreceptors of gustation and olfaction respond to chemicals in aqueous solution Taste receptors excited by food dissolved in saliva

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Special Senses: Smell & Taste

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  1. Special Senses: Smell & Taste The Chemical Senses

  2. The Chemical Senses • Primitive senses to alert us to savor or avoid substances • Chemoreceptors of gustation and olfaction respond to chemicals in aqueous solution • Taste receptors excited by food dissolved in saliva • Smell receptors excited by airborne chemicals dissolved in fluids coating the nasal membrane • 80% of taste is actually smell!!! • Both senses are heightened in pregnant women (due to increased estrogen)

  3. Olfactory epithelium • Pseudostratified epithelium at roof of nasal cavity • Millions of bowling pin shaped olfactory receptor cells • Bipolar neurons • Olfactory cilia covered by thin mucus • Mucus traps and dissolves airborne odorants • Unmyelinated axons project through cribiform plates and synapse in olfactory bulbs • Lifespan 30-60 days (rare neurons that are replaced) • Humans distinguish about 10,000 odors! • Some smells are actually stimulating pain receptors (ammonia, menthol, chili peppers) • Surrounded by columnar cells

  4. Localization & strcuture of Taste BUDS • 10,000 Taste buds! • Few on soft palate, inner cheeks, pharynx, epiglottis of larnyx • Most on papillae (peg-like projections) of tongue • Fungiform papillae • Mushroom shaped over entire tongue • Foliate papillae • Epithelium of side walls • Circumvallate papillae • Large round, form an inverted “V” at back of tongue

  5. Each taste bud: • 50-100 epithelial cells • Gustatory (taste) cells • Microvilli “hairs” extend thru a taste pore and bathed in salvia at surface • Replaced every 7-10 days • Most respond to 2 or more taste qualities • “taste maps” are misrepresentations.. All types of taste can be elicited from all areas of mouth w/taste buds • Basal cells • Stem cells differentiate into new gustatory cells

  6. 5 Basic tastes • Sweet • organic substances including sugars, saccharin, alcohols, some amino acids, and lead salts • Sour • acids (H+) in solution • Salty • inorganic salts (metal ions) • Bitter • alkoloids (quanine, caffiene, nicotine, morphine, and strychnine) and some nonalkoloids such as aspirin • Umami • amino acids glutamate & aspartate (beef taste, MSG, aged cheese) • Homeostatic Value • “likes” of sugar and salt satisfy body's need for carbs and minerals • Acidic foods sources of essential Vitamin C • Natural poisons and spoiled foods are bitter and disliked

  7. Physiology of taste • Chemical must be dissolved in saliva, diffuse into taste pore, and contact gustatory ‘hair’ • Each taste has its own mechanism for inducing release of nuerotransmitters • Induces graded potential eliciting action potentials in nerve fibers • Facial nerve, glossopharyngeal nerve, and vagus nerve conduct impulses to thalmus, gustatory cortex, hypothalmus, and limbic system • Triggers digestive reflexes • increase salivation • Gastric juice secretion • Gagging or vomiting • Different taste receptors have varying thresholds • Bitter – detect in minute amounts • Partial adaptation in 3-5 seconds complete in 1-5 minutes

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