Gustation and Olfaction

Gustation and Olfaction

1. Taste

   • four qualities
     • sweet
     • sour
     • bitter
     • salty
   • taste buds
     • chemical receptors concentrated along the edges and back surface of the tongue
   • umami increases sensitivity of other taste qualities
     • activated by proteins & monosodium glutamate
   • receptors are also found in the roof and back of the mouth
     • even people without a tongue can taste substances
     • hairlike structures project from the top of each cell into the taste pore (opening to the outside surface of the tongue)
     • when a substance is taken into the mouth, it interacts with saliva to form a chemical solution that flows into the taste pore
       • stimulates receptor cells
   • provides us with pleasure
   • has adaptive significance in discriminating between nutrients and toxins
     • newborns respond positively to sugar water and negatively to bitter substances
     • poisonous substances in nature have bitter tastes
       • hard wired into our physiology
     • sweet substances are more likely to occur in nutritious foods

2. Smell

   • receptors for smell are long cells that project through the lining of the upper part of the nasal cavity and into the mucous membrane
   • our ability to discriminate between odours is not well understood
     • most popular theory is that olfactory receptors recognize diverse odours individually rather than by mixing of receptors
   • olfactory receptors
     • have receptor structures that resemble neurotransmitter binding sites on neurons
       • any of potential odour molecules can lock into sites that are tailored to fit them
         • receptors that fire send their input to olfactory bulb
           • forebrain structure immediately above nasal cavity
             • each odorous chemical excites only a limited portion of the olfactory bulb
               • odours are apparently coded in terms of the specific area of the olfactory bulb that is excited
   • pheromones
     • chemical signals found in natural body scents
       • may affect human behaviour in subtle ways
         • no solid evidence to prove that pheromone substances make humans "sexually irresistable"
   • menstrual synchrony
     • tendency of women who live together or are close friends to become more similar in their menstrual cycle

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