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Lecture 8 – Gustation (Taste) (Chemical senses 1)

Raghav RajanBio 354 – Neurobiology 2

February 05th 2015

All lecture material from the following links unless otherwise mentioned:1.http://www.ib.cnea.gov.ar/~redneu/2013/BOOKS/Principles%20of%20Neural%20Science%20-%20Kandel/gateway.ut.ovid.com/gw2/ovidweb.cgisidnjhkoalgmeho00dbookimagebookdb_7c_2fc~38.htm2. Research papers or other links mentioned on slide

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From earlier classes ...!!

● Aperture control (Vishnu)

● Pin-wheel centers – orientation tuning (Ruchi)

● Responses to natural scenes (Radhika)

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Taste – processing, function, etc.

● Chemicals sensed using the tongue

● Good food vs. bad food, poisons, etc.

● Flavour, quality of food

● To ensure that all nutrients are obtained in correct amounts

● How are chemicals sensed?

● Taste coding

– Identity

– Intensity

– Location

– Timing

● Higher order functions

– Food quality

● Texture, smell, temperature, pain – all influence taste (And experience too ...)

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Mouth and nasal cavities are connected

● Food can trigger olfactory receptors – retronasal route

● Taste cells clustered in taste buds

● Tongue, palate, pharynx, epiglottis

http://emedia.leeward.hawaii.edu/hurley/Ling102web/mod3_speaking/3mod3.2_vocalorgans.htm

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Sensing chemicals ...

● Not too much of an issue related to sensing chemicals – been there, done that!!

● Three main types of papillae distributed in different parts of tongue

● Taste buds with taste cells present in papillae

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Taste buds contain taste cells with gustatory receptors

● Many taste cells in a taste bud

● Extend microvilli outside through taste pore

● Taste cells are non-neuronal epithelial cells

● Yet, excitable, can fire action potentials

● Gustatory afferent nerve forms synapses with taste cells

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Basic types of taste stimuli

● Sweet

● Bitter

● Salty

● Sour

● Umami

– relatively new

– Japanese chemist – Kikunae Ikeda identified glutamic acid as the cause for the unique taste of kombu seaweed

– Two Japanese words – umai (delicious) and mi (taste)

– “meaty” taste or taste of monosodium glutamate (Ajinomoto) – may be to sense proteins

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Text book view of how tastes are distributed on the tongue

● 1 – bitter, 2 – sour, 3 – salt, 4 - sweet

● Not true

● Original paper did not

● There can be differences in the threshold

● Taste more evenly distributed throughout the tongue

http://en.wikipedia.org/wiki/Tongue_map

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Taste receptors

● Each taste receptor cell (TRC) can express combinations of receptors

● T1R1/T1R3 – amino acids

● T1R2/T1R3 – sweet

● T2Rs – bitter

● Ion channels – sour and salt

● TRCs release ATP (could also release other transmitters)

● Gap junctions between TRCs

http://www.researchgate.net/profile/Ranier_Gutierrez/publication/6741677_The_neural_mechanisms_of_gustation_a_distributed_processing_code/links/0c96051d19486a500d000000.pdf

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Labelled line vs. distributed code

http://www.biomedcentral.com/1471-2202/8/S3/S5/figure/F1

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Gustatory pathway

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Labelled line vs. distributed code

http://www.biomedcentral.com/1471-2202/8/S3/S5/figure/F1