Gustation and Olfaction

(Taste and Smell)

• chemoreceptors– chemical substance

dissolved in mucus– G-protein-linked receptors

• all smell• some taste

– sweet– bitter– umami (e.g., glutamate)

– channel-linked receptors• some taste

– sour– salt

Rhoades and Pflanzer, Human Physiologycf. Fig. 10-6 Ganong

Taste

• gustatory cells– located in taste buds

of the tongue• also of the pharynx,

epiglottis and soft palate

– about 50 - 100 per bud

– hairs are microvilli

Fig. 16.6

Taste • 5 (or 6) Taste Modalitiesreceived from all parts of the tongue– sour

• H+

– salt• ions, especially Na+ & Cl-

– sweet• various organic substances

– sucrose– phenylalanine

• Pb

– bitter• various organic substances

– alkaloids– many drugs

– umami / savory: a fifth taste• glutamate

– fat: a sixth taste?• long chain fatty acids (via the CD36 receptor)

J. Clin. Invest. 115:3177-3184 (2005)

Neural Pathways• Neural pathways

– facial (VII) and glossopharyngeal (IX) nerves

– medulla and thalamus – parietal lobe and insula

Ganong, 20th edition

Fig. 10-5 Ganong

Smell

• Olfactory cells are bipolar neurons– axons form olfactory

nerve– cribriform plate of

ethmoid bone• roof of nasal cavity• floor of skull

Fig. 16.7

Smell

• Sniffing increases air flow to roof of nasal cavity.

• able to distinguish between thousands of different smells– total number of smell modalities not known– Different smells produce different patterns

of stimulation on different populations of olfactory receptors.

• Smell contributes significantly to the “taste” of food.

Olfactory Pathway

• olfactory nerves (sensory) • olfactory tract (mixed) • temporal lobe portions of limbic system

– thalamic relay NOT required– Smells can rapidly trigger emotional responses.

• pheromones– a chemical released by one animal that produces

an emotional/behavioral response in another animal– probably exist in humans

• may work via olfactory system

Fig. 16.8