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Bio 222 Exam 3
Lec 14 - Taste
11
Biology
Undergraduate 4
11/16/2010

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Term
3 types of papillae (with locations/buds amount)
Definition
1. Fungiform (anterior, few taste buds)
2. Foliate (posterior lat edge, 12-600 buds)
3. Circumvillate (back portion. 250 buds)
Term
tastant
Definition
dissolved ion or molecule that stimulates taste receptor proteins
Term
Taste receptor cell (250 or so in each taste bud)
Definition
Non-neuronal, polarized epithelial cell
Apical surface has:
-microvilli that project into taste pore)
-taste receptor proteins
Basal surface has: synapses on sensory afferents
-each cell has a week lifespan
Term
transduction (for taste)
Definition
how a stimulus in the environment causes and electrical response in a sensory receptor cell
-transduction is how a TASTANT leads to a RECEPTOR POTENTIAL (deoplarization) in the TASTE RECEPTOR CELL.
-depolarization causes neurotrans release (ATP,5HT) from the TRC, causing sensory axon to fire action potentials
Term
Transduction of salt taste: ion channel
Definition
1. Tastant (Na+) enters through amiloride-sensitive Na+ channels (not voltage gated), causing depolarization
2. Voltage-gated ion channels open leading to neurotransmitter release
Term
Transduction of sour taste: ion channel
Definition
1. tastant (H+) enters through some type of cation channel (opens TRPP or closes K+) causing deoplarization
2. Voltage-gated ion channels open leading to neurotransmitter release.
Term
transduction of bitter, sweet and umami tastes: G-protein coupled receptors
Definition
1. Tastant (quinine, glucose, or glutamate binds GPC receptor)
2. G-protein GUSTDUCIN is activated
3. Beta-gamma subunits of gustducin stimulate phospholipase C
4. phospholipase C hydrolizes PIP2 to IP3 and DAG
5. IP3 activates TRP channel (TRPM5)
6. increased intracellular Ca2+ depolarizes cell
7 neurotransmitter is released
Term
Taste receptor proteins: the G-protein coupled receptor type
Definition
BITTER: 30 different types of bitter receptors (T2Rs), receptors consist of two T2R proteins

SWEET/UMAMI: are heterodimers (made up of two diff subtypes), T1Rs
Sweet=T1R2+T1R3
UMAMI=T1R1+T1R3
Term
labeled line encoding
Definition
TRCs of one kind: 1 TRC has one receptor type which releases to one sensory axon
Term
Across-fiber encoding
Definition
multimodal TRCs: 1 TRC has many receptor types to 1 sensory neuron
- or more than one kind of TRC to 1 sensory neuron
Term
Central taste pathways
Definition
-Cranial nerves V11, IX, and X carry taste signals
-The axons project ipsilaterally to the gustatory nucleus in the medulla.
-gustatory nucelus axons synapse on cells in central posterior medial (VPM) of thalamus
-VPM neurons project to gustatory cortex and frontal cortex
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