The chemical senses ( olfaction and taste) Flashcards
when you get a severe cold why do we PERCEIVE that food doesn’t taste as good?
because olfaction component of flavor is 1/3 of the flavor perception
why are olfaction and taste problems important to identify in a pt?
b/c they can indicate more general disease ( serious) states.
what is special about the sensory capacity of gustatory (taste) and olfactory receptors?
they can maintain sensory capacity despite death of old receptor elements and recruitment of new elements ( new olfactory neurons and new taste receptor cells respectively).
Where does a large % of CSF flow out of in the olfaction/gustatory system and what is the implication of this?
the cribiform plate and this is a problem because it serves as a conduit for viruses to get into the nervous system.
where are the olfactory cell bodies located?
in the olfactory epithelium lining below the cribiform plate
where do the axons of the olfactory system travel to relay info?
via the axonal projections through the cribiform plate to the olfactory bulb
what are the 4 olfactory bulb targets?
pyriform cortex ( olfactory cortex), olfactory tubercle, amygdala, entorhinal cortex
from the amygdala where in the brain does the olfactory neuron travel?
orbitofrontal cortex ( emotional association),thalamus and hypothalamus
from the entorhinal cortexwhere in the brain does the olfactory neuron travel?
hippocampal formation ( memory association)
what capacity do olfactory epithelial basal cells have ?
they can replenish epithelium as mature sensory neurons die
what is anosmic?
can’t smell
what is parosmia
a change in the perception so that something doesn’t smell the way it usually does ( this can happen after exposure to extreme toxins b/c the neurons die and regenerate but regenerate incorrectly.)
How long do sensory neruons last?
30 days
what is the largest g protein coupled system in the body?
olfaction
when an odorant interacts with a receptor protein what happens?
depolarization of the receptor potential occurs and cAMP increases via activation od adenly cyclase , cAMP binds an ion channel and opens it depolarizing the cell and letting Ca2+ in .
Ca2+ leads to Cl- channel opening which gives the olfactory signal a boost.
how many olfactory receptors do we have?
1000s
explain the specificity of odor receptors
they have some specificity but are promiscuous, i.e. compounds with similar chemical structure may use similar or same receptors.
There isn’t an orange or a rose receptor.
what is the structure of the olfactory receptor?
a 7 transmembrane domain. all receptors have amino acid sequence homology.
what is the distribution of the olfactory receptors?
they are split up into quarters with 1/4 residing in each zone.
How many olfactory receptor types does a neuron express?
only one
How are neurons expressing a particular olfactory receptor distributed?
homogenously or they can have a clustered distribution pattern
How does the number of Odor receptors correlate to the number of odorants?
one odor receptor can respond to a lot of different odorants which share a common molecular feature.
how do olfactory neurons encode information?
by virtue of spatial pattern
where do similar patterns of olfactory receptors coalesce?
in the glomeruli of the bulb below the cribiform plate
what do the mitral and tufted cells in the bulb do?
they are relay neurons that project to the olfactory cortex
what are periglomerular cells and granule cells?
they are inhibitory interneurons that modulate activity of the mitral tufted cells.
what is the outermost shell of the olfactory neuron?
the periglomerular cells
all neurons expressing a particular olfactory receptor______________
converge onto the same set of glomeruli
what happens to people who have specific anosmias?
they can’t discriminate between certain smells
what is an odotope?
a single chemical moiety that Olfactory receptors recognize ( e.g. a phenyl group)
what is the unit for recognizing a particular odotpe?
1 glomeruli
what is the lateral inhibitory mechanism in the olfactory system?
it is the mechanism by which only maximally stimulated sensory neurons ( e.g. an 8 carbon structure) is pass “information” (smell in this case) along, where as incidentally stimulated sensory neurons ( e.g.. given above e.g. 5,6,7,9, and 10 carbon structures) ( activated due to a high stimulus) are filtered out by the granule cells at the level of the mitral and tufted cells so that only the maximally stimulated substance is perceived.
what are the 5 tastes qualities?
salty, sweet, bitter, sour, and savory ( umami)
which cranial nerves innervate the taste buds?
VII facial via the chord tympani to tongue and the greater petrosal to the palate ( anterior 2/3 tongue)
and glossopharyngeal ( posterior 1/3 tongue), and vagus ( epiglottis)
how many taste cells does each axon innervate?
2-10 taste cells
what do gustatory axons innervate?
the nucleus tractus solitarius
after the information from the neurons for taste travel tothe NTS in the brain, where does it go?
to the ventral posterior medial (VPM) nucleus of the thalamus and from there to the hypothalamus, and amygdala.
what are the taste buds of the soft palate , circumvallate, foliate and fungiform papillae, most sensitive to?
sweet
where is sweet and savory ( umami) most sensitive?
the anterior portion of the tongue
where is salty most sensitive?
the anterior perimeter of the tongue
where is sour most sensitive?
the lateral tongue
where is bitter most sensitive?
the posterior of the tongue
where are the taste buds located?
in specialized protrusions called papillae
Describe taste receptors
they are taste receptor cells not neurons and they last 10 days after which the basal cells replenish them ( self renewal)
which 2 tastes are transduced through ionic transduction which results in an increase in calcium and transmitter release?
salt ( Amiloride -sensitive sodium channel) and sour (H+ -sensitive channel)
What tastes are transducer via second messenger ?
bitter,sweet and umami.
increase in cAMP–> stimulation of a TRPM5 Ca2+ channel via IP3
What is the heterodimer in the second messenger sys for sweet?
T1R2 and T1R3
What is the heterodimer in the second messenger sys for umami?
T1R3 and T1R1
What is the homodimer n the second messenger sys for bitter?
T2R
How does the trigeminal nerve contribute to taste/
it contributes pungency ( irritation ), which is activated by capcacin in spicy food for e.g..
this must be distinguished from odor and taste
what does the labeled line taste coding demonstrate?
that if you remove a homo or heterodimer and remove phospholipase C which is in all taste cellsand then replace them both you will get only the one with the homo/heterodimer removed and the rest will not be restored.
