CHAPTER 8.docx

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22 Apr 2012
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CHAPTER 8
- Chemical sensation is the oldest and most common of the sensory systems
- Chemoreceptors: chemically sensitive cells
- Gestation and olfaction both detect environmental chemicals; must use both to perceive
flavor
Taste
The Basic Tastes
- Saltiness, sourness, sweetness, bitterness, and umami (delicious; defined by savory taste
of the amino acid glutamate; monosodium glutamate, MSG)
- Artificial sweeteners are 10,000-100,000 times sweeter than sucrose
- Bitter substances range from simple ions like K+ (KCl evokes bother bitter and salty
tastes) and Mg2+ to complex organic molecules such as quinine and caffeine
- How do we perceive the countless flavors of food?
Each food activates a different combination of the basic tastes
Distinctive flavor as a result of their taste AND smell occurring simultaneously
Other sensory modalities such as texture and temperature and pain sensations
(spicy foods)
The Organs of Taste
- Taste is primarily a function of tongue, but regions of pharynx, palate, and epiglottis have
some sensitivity
- Odors can also pass via pharynx into nasal cavity where detected by olfactory receptors
- Tip of tongue most sensitive to sweetness, back to bitterness, and sides to saltiness and
sourness
- Papillae: small projections scattered on the surface of the tongue,
Ridges foliate papillae
Pimples vallate papillae
Mushrooms fungiform papillae
- Each papillae has from one to several hundred taste buds
- Each taste bud has 50-150 taste receptor cells/taste cells
- Taste cells are only about 1% of the tongue epithelium
- Taste buds also have basal cells that surround the taste cells, plus a set of gustatory
afferent axons
- Typical person has 2000-5000 taste buds
- Threshold concentration: concentration of stimulus needed to evoke a perception of taste
- Just above threshold, most papillae tend to be sensitive to only one basic taste
- When concentrations of the taste stimuli are increased however most papillae become
less selective
Taste Receptor Cells
- Chemically sensitive part of a taste receptor cell is its small membrane region called the
apical end, near surface of tongue
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