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Chapter 8

CHAPTER 8

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Department
Neuroscience
Course
NROC64H3
Professor
Niemier
Semester
Winter

Description
INTRODUCTION Gustation and olfaction have a similar task the detection of environmental chemicals In fact only by using both sense can the nervous system perceive flavour However the systems of gestation and olfaction are separate and different from the structures and mechanisms of their chemoreceptors to the gross organization of their central connections to their effects on behaviour The neural information from each system is processed in parallel and is merged at rather high levels in the cerebral cortex TASTE The Basic Tastes It is likely that we can recognize only a few basic tastes Most neuroscientists put the number at five The four obvious taste qualities areSaltinessSournessSweetnessBitternessUmami How do we perceive the countless flavours of foodFirst each food activates a different combination of the basic tastesSecond most foods have a distinctive flavour as a result of their taste and smell occurring simultaneouslyThird other sensory modalities contribute to a unique foodtasting experience eg texture temperature and pain sensationsThe Organs of Taste Although we taste with our tongue there are other areas of the mouth eg palate pharynx and epiglottis that are also involved Odours from the food pass via the pharynx into the nasal cavity where they can be detected by olfactory receptorsThe tip of the tongue is most sensitive to sweetness the back to bitterness and the sides to saltiness and sourness However most of the tongue is sensitive to all basic tastesThe surface of the tongue is scattered with small projections called papillae Each papilla has from one to several hundred taste buds see Fig 82 and each of these have 50150 taste receptor cells Taste cells make about 1 of the tongue epithelium Taste buds also have basal cells that surround the taste cells and a set of gustatory afferent axons A person typically has 20005000 taste budsTastants at very low concentrations will not be tasted but at some critical concentration the stimulus will evoke a perception of taste This is the threshold concentration At levels just above threshold most papillae tend to be sensitive to only one basic tasteHowever when the concentrations of the Tastants are increased most papillae become less selective For
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