Chemical Senses Lec09 Flashcards
____ has no major, direct cortical
projections or thalamic input
Olfaction
Olfactory Epithelium has 3 cells:
basal (stem) cells, neurons, & supporting cells
___ cells in the olfactory epithelium renew every 30 days
basal
neurons in the olfactory epithelium are ___polar
bipolar
what do neurons of the olfactory epithelium need to survive?
contact with & tropic support from olfactory bulb to survive
describe signal transduction of smell
–> odorant binds to G-protein receptor (R)
–> G protein (G) & adenyl cyclase (AC) increase
–> cAMP levels increase
–> cyclic nucleotide gated (CNG) ion channel opens
–> cell depolarizes
key ion in smell pathway?>
calcium
Humans have about ___ odorant receptors
1000
1 neuron = ___ odorant receptor type
1
1 odorant receptor type recpgnizesone ___
compoenent of an odorant molecule
odorant encoding is based on a
pattern of responses
*not single neurons
what are the 4 layers of the olfactory bulb?
glomerular, external plexiform, mitral cell, granule cell
what layers in the olfactroy bulb go right to the olfactory cortex
mitral and tufted cells
___ and ___ cells are inhibitory interneurons that modulate mitral & tufted cells
periglomerular and granule
what is the outermost layer?
periglomerular
olfactory neurons projections to CNS is either
1) quadrant-to- quadrant
(2) same-OR-neurons-to-same-glomerulus
weak stimulations are removed via ____ cells, so only the most sensitive / maximally stimulated neuron responds to an odorant.
granule cells
Each glomerulus recognizes different ___
odorants
each odorant receptor recognizes a specific
“odotope”
Odors are identified by overall activation pattern of
glomeruli across the whole bulb
taste invovles innervation by what cranial nerves
7, 9, 10
Gustatory axons innervate the nucleus of the
___ in brainstem
solitary tract (NTS)
the solitary n. of the braisntem projects to the
VPM in the thalamus
what cranial nerve converys oral irratation (the common chemical sense)
trigem
Four primary taste fields = areas of \
greatest sensitivity
Taste buds are all on ___.
papillae
Each bud has ___ receptor & basal (stem) cells
50-100
Microvilli on ___ taste cells _get initial stimulus _
Type II
Microvilli on Type II taste cells get initial stimulus then goes to
gap junctions
Microvilli on Type II taste cells get initial stimulus –> gap junction –> ___ cells
type III
type III cells pass synaptic transmission to
gustatory afferent axons
what tastes use IONIC Transduction Mechanisms
sweet and sour
Sweet, Bitter, and Umami (amino acids) use Receptor-Mediated Transduction via___
2nd
Messengers
Pattern code theory of taste encoding
tastes are encoded by differential firing pattern across a population of axons.
what supports pattern code theory of taste encoding
supported by single axons responding to many different
primary stimuli, although they have a maximal response
to only one stimulus.
what is the labeled line theory of taste encoding
each neuron/axon is responsible for one specific taste.
what supports the labeled line theory of taste encoding
specific gene knockouts that can rescue
or delete the perception of individual taste qualities.
ex. deletion of PLCβ2 causes loss of sucrose, glutamate, and quinine tastes.
where are the cell bodies of the enurons that transduce odors?
in the olfactory epithelium
In humans the OE lines the posterodorsal part of the nasal cavity below the
cribriform plate
The OE neurons relay information via axonal projections through the cribriform plate to the ___
olfactory bulb
Bulbar neurons project to the___
piriform cortex
Bulbar neurons project via the ____ to the piriform cortex
lateral olfactory tract
where does the oflactory sensory information go to after leaving the piriform cortex?
- to parts of the neocortex via the mediodorsal nucleus of the thalamus
- and to the lateral hypothalamus.
each neuron in the oflactory epithelium has a ___ axon that projects to the bulb
c fiber (a thin unmyelinated axon)
epithelial projections are continually being broken down and reforming due to
basal cells always undergoing mitotic division in stem cell mode
All of the G protein activating receptors have a common tertiary structure with___ transmembrane domains
7
Neurons expressing a particular OR are located where?
they are limited to a particular region (or zone) of the epithelium.
Within a zone, neurons expressing a particular OR can be either:
homogeneously distributed or have a clustered distribution pattern.
the___ a neuron expresses determines the physiological responsiveness of that neuron.
particular odorant receptor
any one OR is broadly tuned to respond to a lot of different odorants, which share a
common molecular feature.
each ___ has a unique pattern of spatial activity
odorant
order of the layers of the olfactory bulb (from closests to farthest from the sensory neuron)
glomerular layer, external plexiform layer, mitral cell layer and granule cell layer.
periglomeruli cells cluster around
glomeruli
Unlike other sensory systems the projection of the sensory surface onto its central structures is not
NOT point-to-point.
olfactory neurons are ___ tuned
broadly
where is there pattern activation in response to odorants?
- in the epihtelium
- in the bulb
in the consensus working model
there are many different ORs and each would recognize a___) that would be considered an “odotope
single chemical moiety (e.g., a phenyl group
A single chemical would be composed of how many odotypes?
many
How many odotopes are there likely to be?
As many as there are OR types.
under the ___ model..
Odors would be identified and discriminated by the overall activation of glomeruli across the whole bulb.
consensus working
what does the solitary n. projec tto
- vpm
- hypothalamus
- amygdala
what are the 4 primary taste fields?
The circumvallate, foliate and fungiform papillae, as well as taste buds
what do all taste fields respond to?
all tastants
each___ is most sensitive to a particular taste quality.
taste field
Salt and sour stimuli are transduced through an ionic transduction mechanism which results in an intracellular increase in _____ and transmitter release.
calcium
with sweet, bitter, umami,
increases in ___ stimualte a TRPM5 calcium channel
camp
with sweet, bitter, umami ncreases in cAMP stimulate a TRPM5 calcium channel via ___
IP3.
