CSB332H1 Study Guide - Midterm Guide: Taste Bud, Olfactory System, Olfactory Tract

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Published on 17 Aug 2012
School
Course
CSB332H1S L20 (no L19, prof took up test instead); March.28, 2012
Sensory Systems
Transduction in Olfactory Cilia
Signal transduction cascade
Increases [cAMP] influx of Ca, Na
Ca influx opens Cl channel Cl leaves more depolarization
Chemical Amplification
Olfaction depends upon chemical amplification in order to yield
sensitivity
Chemical amplification - 2nd msger pathways in which enzymatic
cascades produce large #s of intermediate products to be activated (ex.
cAMP)
increasing by 1000x the effect of one activated rec molec
Odorant Specificity
Humans can discriminate odors due to 1000s of dif olfactory recs
Each olfactory rec recognizes spectrum of odors rather than being
highly selective
Each particular odorant rec is found in restricted area of olfactory
epithelium
o Dif families of R genes expressed in zones extending along
length of epithelium
Central olfactory pathways
Neurons from lateral olfactory tract project to;
1. Limbic system (amygdala, entorhinal cortex, hippocampus,
subiculum). Ancient region of brain (motivation, emotion,
certain kinds of memory)
o Cues to lay down & recall these memories
2. Thal frontal cortex for recognition.
o To primary olfactory region for processing
Olfaction & Gender
Olfactory sensitivity can be induced in humans
o Ex. humans who were initially unable to smell volatile steroid
androstenone developed ability after repeated brief exposure
Humans can show enhanced sensitivity to odors they could previously
detect
o Avg increase of 5-fold only observed in females of
reproductive age
o Suggests greater olfactory sensitivities among females may be
associated w female reproductive bhvrs such as pair bonding
& kin recognition
Also in mice, rats
Nature Neuroscience 2002 Volume 5 p. 20
Anosmia
A condition where sense of smell is reduced or lost entirely
Caused either by traumatic head injury (permanent) or a virus
(temporary)
Some people are born w/o sense of smell -congenital anosmia
Some develop it as a conseq of another disorder
o Ex. Alzheimer's disease.
Some anosmics suffer from depression& quality of life severely
affected atm little that can be done to help
o Since regulates emotional bhvr in significant way
TASTE (GUSTATION)
Taste & Smell often associated
o 1 reason: Both senses activated by external chemical stimuli
Some taste stimuli (tastants) also act on G-prot coupled recs similar
to odorants
o Structural similarities
Other tastants act directly on membrane conductances
75% of what we perceive as taste comes from sense of smell
o Odorants can’t go form mouth to nose when have a cold lost
hald of odorant info in nasal cavity; have a lot of mucus
Taste Receptor Cells
Taste Rs = ciliated neuroepithelia cells found in taste buds
Regenerated throughout life
Don’t have axons
o Short recs
Form chemical synapses w afferent neurites in taste bud
Microvilli project from taste cell into taste bud where they are
bound by tastants (dissolved in saliva)
Tastants are divided into:
1. Salt
2. Sour
3. Bitter
4. Sweet
5. Umami
o (MSG amino acid taste)
2 broad categories of transduction mechanisms for these 5 tastants:
1. Direct action on ion channels
2. 2nd messenger activation
Salt & Sour
Taste of salt direct flux of Na+ thru channels in apical
membrane of outside of taste cell
Salty foods contain high [Na+]
o Diffuses down conc grad into taste cells
o Salt induced depolarization transmitter release from
taste cell onto afferent neurons act pot
Salts & acids can permeate ion channels in sensitive ending or block
normally open K+ channels
Sour taste high [proton] in acidic foods
Sometimes Protons block K+ channels depolarization
Sweet & bitter substances tend to be large molecs bound by
macromolecular recs w high specificity
Sweet & bitter tastants activate 2nd msger pathways thru interaction
w G protein-coupled recs
Bitter ex. quinine
Molecular Receptors for Chili
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Document Summary

Csb332h1s l20 (no l19, prof took up test instead); march. 28, 2012. Ca influx opens cl channel cl leaves more depolarization. Olfaction depends upon chemical amplification in order to yield sensitivity. Chemical amplification - 2nd msger pathways in which enzymatic cascades produce large #s of intermediate products to be activated (ex. camp) Increasing by 1000x the effect of one activated rec molec. Humans can discriminate odors due to 1000s of dif olfactory recs. Each olfactory rec recognizes spectrum of odors rather than being highly selective. Each particular odorant rec is found in restricted area of olfactory epithelium: dif families of r genes expressed in zones extending along length of epithelium. Neurons from lateral olfactory tract project to: limbic system (amygdala, entorhinal cortex, hippocampus, subiculum). Ancient region of brain (motivation, emotion, certain kinds of memory) Cues to lay down & recall these memories: thal frontal cortex for recognition, to primary olfactory region for processing.

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