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Lecture 6

Lecture 6 - Sensory Processing II

7 Pages
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Department
Psychology
Course Code
PSY290H1
Professor
Franca Placenza

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Taste Stimuli
1.The basic taste stimuli
oSaltiness
oSourness
oSweetness
oBitterness
oUmami = the taste of meat (savory)
2.Tongue
oPrimary taste organ
oCovered with papillae
o3 types of papillae
Circumvallate papillae - largest, found at back of tongue, are 9
50% of cell receptor cells occur by these
Foliate papillae - second largest, found on sides of tongue
Fungiform papillae - smallest, found near tip of tongue
Contain 6 taste buds each
oEach papillae :
Contains several hundred taste buds
Taste buds are clusters of taste receptor cells
3.Taste receptor cells
oSaliva has access to these (in the crevasses of the papillae)
oProject toward the surface of the tongue
Apical end has thing extensions (microvilli - an opening that saliva
enters in) that are clustered in taste pores
Basal end innervated by gustatory nerve fibers
oBasal cells - progenitor cells which become new taste cells every 2 weeks
Are the baby cells that make the new taste receptor cells
Not all sensory systems have regenerating cells
Chemotransduction in Taste Cells
4.Saltiness
oSalt-sensitive taste cells have special Na+ channel (different than ones
discussed before)
EX = amiloride-sensitive sodium channel
Always open channels that recognize sodium
oNa+ in salty foods enter cell through amiloride-sensitive sodium channel
resulting in depolarization
Current passively spreads down
oVoltage-gated Na+ and Ca2+ channels open in response to depolarization,
triggering neurotransmitter release
These channels found near the bottom of the cell (different from ones
above)
Ca2+ allows vesicles to produce (similar as in neurotransmitters)
5.Sourness
www.notesolution.com
oMostly acidic foods >> dissolved acids generate H+ ions
oH+ ions block K+ channels by binding to the channels, preventing K+ efflux
(leaving the cell) >> results in depolarization and transmitter release (build up of
K+ within the cell)
K+ channels are normally open and leaves the cell
oH+ ions can also enter taste cell through amiloride-sensitive sodium channel
and depolarize cell
Also have Ca2+ and Na+ voltage-gated channels at the bottom of the
cell
6.Bitterness, Sweetness, Umami
oThese tastes bind to taste receptors
o2 families of taste receptors
T1R = 3 types >> T1R1, T1R2, T1R3
T2R = at least 30 distinct types
All G-protein receptors
oSweet > tastant binds to a heterodimer (combination) of T1R2 and T1R3
receptors (must bind to both in order to be perceived)
T1R2 and T1R3 are found on one taste pore (??)
oUmami >tastant binds to a heterodimer (combination) of T1R1 and T1R3
receptors
T1R1 and T1R3 are found in the same place
oBitter > bind to T2Rs
7.All receptor cells send transmitter that is believed to be the same for every taste
stimuli
Central Taste Pathways
8.Taste information carried by gustatory nerve fibers
9.Carried by 3 cranial nerves and innervate gustatory nucleus in medulla (VII, X, IX)
10.Neurons of gustatory nucleus project to ventral posterior medial nucleus (VPM) of
thalamus
11.VPM neurons project to primary gustatory cortex
oInsula - taste perception within the same area of the brain, also involved with
emotions
Taste Discrimination
12.Distinct tastes are discriminated by distinct firing patterns of gustatory neurons
13.Taste receptor cells are not that selective
oRespond to more than one taste (although differentially)
oSome gustatory neurons are differentially sensitive to certain tastes (others
are not)
The higher up into the brain, the more selective each nerve becomes
www.notesolution.com

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Description
Taste Stimuli 1. The basic taste stimuli o Saltiness o Sourness o Sweetness o Bitterness o Umami = the taste of meat (savory) 2. Tongue o Primary taste organ o Covered with papillae o 3 types of papillae Circumvallate papillae - largest, found at back of tongue, are 9 50% of cell receptor cells occur by these Foliate papillae - second largest, found on sides of tongue Fungiform papillae - smallest, found near tip of tongue Contain 6 taste buds each o Each papillae : Contains several hundred taste buds Taste buds are clusters of taste receptor cells 3. Taste receptor cells o Saliva has access to these (in the crevasses of the papillae) o Project toward the surface of the tongue Apical end has thing extensions (microvilli - an opening that saliva enters in) that are clustered in taste pores Basal end innervated by gustatory nerve fibers o Basal cells - progenitor cells which become new taste cells every 2 weeks Are the baby cells that make the new taste receptor cells Not all sensory systems have regenerating cells Chemotransduction in Taste Cells 4. Saltiness o Salt-sensitive taste cells have special Na+ channel (different than ones discussed before) EX = amiloride-sensitive sodium channel Always open channels that recognize sodium o Na+ in salty foods enter cell through amiloride-sensitive sodium channel resulting in depolarization Current passively spreads down o Voltage-gated Na+ and Ca2+ channels open in response to depolarization, triggering neurotransmitter release These channels found near the bottom of the cell (different from ones above) Ca2+ allows vesicles to produce (similar as in neurotransmitters) 5. Sourness www.notesolution.com
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