*besides vision! Sensory “connections” Olfaction Taste Hearing Touch.
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Transcript of *besides vision! Sensory “connections” Olfaction Taste Hearing Touch.
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*besides vision!
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Sensory “connections”
• Olfaction• Taste• Hearing• Touch
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Olfaction
• Extremely discriminating-even between odorant enantiomers
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Olfaction• In late 80’s odorant
receptors were cloned from cilia
• These were 7TM helix G-protein receptors (OR) stimulating a unique G protein, Golf
• Human OR genes number 500 but only about 30 are not pseudogenes!
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Olfaction• Each neuron expresses only 1 OR
• Golf stimulates Ad. Cyclase
• cAMP opens cation channels;depolarization occurs; action potential propagates
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Olfaction• Decoding of olfactory
stimuli -in mouse suggests a combinatorial mechaism
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Olfaction• All neurons
expressing a given OR converge on a discrete area in the olfactory bulb
• The spatial pattern of OR stimulation is somehow transformed to a unique scent.
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Taste
• More limited scope of possible tastes• Olfaction contributes to complex tastes
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Taste
• Gustation receptors are located in different areas
• In taste buds (~150 cells w/ sensory neurons) in papillae (big knobs)
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Taste-Bitter• So far only bitter receptors (G-protein
Receptors) with G, gustducin have been found• There are 50-100 genes (for bitter?) in the
genome but they are mixed on taste buds
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Taste• Bitter receptors ? Stimulation by
specific bitter substance of mT2R• But different ones get mixed up in
brain
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Taste-Salty
• Salt receptors ? Direct sensation by Na+ ion channels blocked by Amiloride
• Analogous to the 4 subunit type channels (like K+)
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Taste-Sweet
• Not isolated in humans but likely G-protein since gustducin knock-out mice can’t taste sweet substances
• Tre 1, a sugar responsive GPR has been found in flies
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Taste-Umami
• Japanese-Deliciousness• Lots in protein rich foods
like soy sauce, roasted meat and and vegemite!
• Na+ Glutamate is the key (1903-Kikunae Ikeda)
• A GPR sensitive to glutamate in the brain is clipped by 309 amino acids in the buds to give low affinity umami receptor.
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Hearing• Mechanical stimulation of hair cells in
cochlea is the key• Hair cells are specialized neurons
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Hearing• Displacement of bundle by 3 Å results in
a measurable membrane potential change (like 1 inch movement at the top of the Empire State building)
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Hearing• Tip link seems to pull
open an ion “hatch”; a mechanosensory channel
• Back and forth flow induces an oscillating ion current
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Touch
• Hot, Cold• Pressure• Capsaicin/hot receptor • Cold/menthol receptor
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Capsaicin and friendsCapsicum (chili pepper)
OH
H3CO
NH
O
capsaicin
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Touch• Example: Capsaicin• Capsaicin/hot receptor • Reacts to noxious stimuli (heat, acid]• Also involved in taste
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• The receptor, VR1, is involved in nociception (pain sensation) as well.
• Used medicinally to alleviate pain by the principle of counterirritation
• How does this work?
Touch-Capsaicin
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QuickTime™ and aGIF decompressorare needed to see this picture.
UCSF Study Suggests Capsaicin Significantly Reduces Debilitating Nerve Pain. Mice without it don’t experience pain from heat (Science,2000).
neurogenic inflammation
capsaicin
Ca++
capsaicin receptor capsaicin activated channel
Substance P
Sensory nerve terminal
Time