lecture 8 – gustation (taste) (chemical senses 1)raghav/pdfs/neurobiology2/... · 3 taste –...
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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