CHEMICAL SENSES

1
CHEMICAL SENSES

• Olfaction
• Receptors
• Olfactory Pathway
• Taste
• Basic qualities
• Receptors
• Taste Pathway
• Supertasters

2
Chemical Senses

• Smell and taste detect chemicals that come into
  contact with receptors
• Chemical senses act as gatekeepers,
  determining which things the body should consume

3
Olfactory Receptors

• Chemicals stimulate cilia on olfactory sensory
  neurons
• Located in olfactory mucosa
• Cilia contain olfactory receptors
• Receptors replaced every 5-7 weeks

4
Olfactory Receptors

• About 350 types of receptors (in humans)
• Odorants cause different patterns of responses
  across receptors (recognition profiles)
• Combinatorial code

5
Olfactory Pathway

• Trigeminal Nerve carries information from
  olfactory receptors
• Olfactory bulb contains glomeruli where OSN
  fibers have synapses
• Amygdala (limbic system)

6
Olfactory Pathway

• Primary Olfactory Cortex (Piriform) - under
  temporal lobes
• Secondary Olfactory Cortex (Orbitofrontal) -
  frontal lobes near eyes

7
Taste Basic Qualities

• sweet - sugar hydroxyl
• sour - hydrogen ions
• salty - sodium ions
• bitter - bases
• umami (savory) - MSG

8
Taste Receptors

• papillae contain taste buds
• taste buds contain taste cells
• tips of taste cells are taste pores
• receptor sites are located on the taste pores

9
Taste Receptors

• areas on the tongue are sensitive to all 5
  qualities, but areas differ in sensitivity
• center of the tongue has no taste receptors
• taste receptors are also located in the mouth
  and throat
• receptors replaced every 10 days

10
Taste Pathway

• Chorda Tympani Nerve front and sides of tongue
• Glossopharyngeal Nerve back of tongue
• Vagus Nerve mouth and throat

11
Taste Pathway

• Nucleus of the Solitary Tract (NST) in brain
  stem
• thalamus
• frontal lobes
• Insula
• Frontal operculum cortex
• Orbitofrontal cortex (bimodal taste/smell
  neurons)

12
Supertasters

• Sensitivity to the bitter taste of PROP is
  genetically based
• Supertasters are especially sensitive
• Higher density of taste buds
• Lower threshold for bitterness
• Differences in types of taste receptors