CHEMICAL SENSES• Olfaction– Receptors– Olfactory Pathway

• Taste– Basic qualities– Receptors– Taste Pathway– Supertasters

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

Olfactory Receptors• Chemicals stimulate cilia on olfactory sensory

neurons• Located in olfactory mucosa• Cilia contain olfactory receptors• Receptors replaced every 5-7 weeks

Olfactory Receptors• About 350 types of receptors (in humans)• Odorants cause different patterns of

responses across receptors (recognition profiles)

• Combinatorial code

Olfactory Pathway

• Trigeminal Nerve carries information from olfactory receptors

• Olfactory bulb: contains glomeruli where OSN fibers have synapses

• Amygdala (limbic system)

Olfactory Pathway

• Primary Olfactory Cortex (Piriform) - under temporal lobes

• Secondary Olfactory Cortex (Orbitofrontal) - frontal lobes near eyes

Taste: Basic Qualities

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

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

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

Taste Pathway

• Chorda Tympani Nerve: front and sides of tongue

• Glossopharyngeal Nerve: back of tongue• Vagus Nerve: mouth and throat

Taste Pathway

• Nucleus of the Solitary Tract (NST) in brain stem

• thalamus• frontal lobes:– Insula– Frontal operculum cortex– Orbitofrontal cortex (bimodal taste/smell

neurons)

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