Reasons relatively little is known about olfaction

Classifying odor qualities

Henning's odor prism

The stereochemical theory of odor

Structure of the olfactory system

Nasal cavity, turbinate bones, olfactory epithelium, cilia, mucus, olfactory bulb (glomeruli)

Two neural circuits

Olfactory bulb-->medial dorsal nucleus of the thalamus --> orbito-frontal cortex

Olfactory bulb-->limbic system (amygdala, hippocampus)

Olfaction and communication: Pheromones

Examples in lower organisms

Impact of odors on human behavior


Taste qualities

Salty, sour, sweet and bitter

Henning's taste tetrahedron

Evidence these are the qualities of taste

Consistency across subjects

Water taste

Physical properties that underlie taste qualities

Structure of the taste system

Taste buds

Papillae (filiform, fungiform, foliate, circumvallate)

Neural projections

Cranial nerves

Chorda tympani (from front & sides)

Glossopharyngeal (from back of tongue)

Vagus (from mouth & throat)

Project to solitary nucleus (medulla)

--> ventral posterior nucleus of the thalamus

--> postcentral gyrus & insula cortex

Neural codes

Evidence for specificity


Bitter: activates intracellular stores of Ca++

Sweet: via cAMP closes K+ channel

Sour: H+ blocks voltage dependent K+ channel

Salt: Na+ binds to channels & pass into cell

Factors affecting taste


Internal state of the organism


Specific hunger

Role of learning

Conditioned taste aversion

Chili peppers and endorphins


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