Exam2Lec1ChemSenses-Olfaction&Gustation Flashcards
Human can discriminate how many olfactory stimuli?
> 1 trillion olfactory stimuli
each with very specific pathways
What type of neuron is OSN?
Bipolar
dendrites form clilia (located at the surface of epith w/ recept)
In the olfactory epthelium, what can we find?
olfactory neurons, support cells, and basal cells
400-500 genes in the human genome codes for how many olfactory receptors?
1,000
Where does the olfactory neurons project its axon?
through crubiform bone into the olfactory bulb where they synpase with central nerv system neurons and they project to diff parts of the brain.
Odorants tend to small volatile molecules that are
a. water soluble?
b. lipid soluble?
Lipid soluble
What does benzaldehyde and benzoic acids smell like?
benzaldehyde: almond
benzoic acids: urine
True or false: There are many sep genes responsible for diff odor receptors
true
there is a huge family of odor receptors in mammalian gene
How many transmembrane domains does odor receptors have?
7
Odor receptors are
A. nicotinic ACH
B. GPCR
C. muscuranic ACH
D. GlyR
GPCR
ORs detect odorants based on what?
Size, charge, amino acid group, vibration
Specific OR mRNAs are expressed where?:
Specific regions of the olfactory epithelium, suggesting a topographic distrubutions
Why is the ORN sensitive?
It expresses a single subtype of OR
OR are expressed in diff areas b/c each OR neuron expresses only 1 type of OR , BUT each neuron can respond to many odor stimuli
True or false: a single OR nerve (ORN) can respond only to one odorant.
FALSE is can repsond to single or multiple odorants
What are the specialist receptors/organs?
Trance-amine associated receptors and vomeronasal organs
Trace-amine associated receptors are found where? What does it use as as signal transduction? What is it highly selelctive for?
- Found in all mammals, including humans
- Uses Golf/cAMP signal transduction mechanisms (taar)
- Highly selective and sensitive for specific pheromones
they are highly specialized w/in olfact epith and they are very rare, They are selctive in their activation
Where can you find vomeronasal organs? What does it contain?
- Found in non-ape mammals excluds humans
- Contains specialist receptors specific to pheromones
these express vomeronasal receptors, not odor receptors
1st rout of activation of OR is via release of olfactory G-protein (GOLF), explain this process
- Odorant molecule binds to receptor protein. Golf is released, activating adenylate cyclase, producing cAMP, which binds and opens a cyclic nucleotide gated (CNGA) channel; (Na/Ca2+ influx (depolarization)
- Ca2+ activates Cl- channel: Cl- efflux (further dep)
- Depolarization triggers ap
- Ca2+ lvsl restores by exchanges and pumps
like Gs
lots of dep bc lots of neg charge leaving and pos charge coming in
What types of olfactory adaptation do we have?
Initial, short-term, long term
What is initial adaptation?
Incr Ca2+ binds to Ca2+ binding protein (CBP) that desentitizes the CNGA channel
like a neg feedback
What is short-term adaptation?
Incr desensitization via Ca2+ calmodulin protein kinase 2 acting on Adenylate cyclase (AC)
What is Long term adaptation?
Ca2+ mediated NO production stimulated guanylate cyclase to produce cGMP (cG)
cGMP causes persisant Ca2+ influx thru CNGA channe; leading to further desensitization of CNGA and AC
What is the 2nd route of activation of OR?
Via release of Olfactory G-protein (Golf)
acts like gq
activates PLP C -IP3 pathway which opens Ca2+ channels
Axons of the ORN synapse where?
In the glomeruli of the olfactory bulb (OB).
The glomeruli of the OB receives info from how many ORN and how many ORN axons?
Each glomerulis receives info from only ONE type of ORN but receives THOUSANDS of ORN axons which synapse with 20-50 relay neurons (mitral/tufted)
The OB can be diveded into how many layers?
5
What are the 5 layers of the olfactory bulb?
- ORN/OSN
- Odorant specific glomeruli (synapses)
- external plexiform layer
- mitral cell layer
- granule layer
What is the mitral/ tufted layer of the olfactory bulb general fxn?
Receive info from OLN in glomerulus and relay up to olfactory tract in CNS.
What is the granule cell layer of the olfacgtory bulb generally involved in?
involved in incr or decr lateral inhibition effectivess
Where info from periphery enters CNS
Glomerulus
What increases odor discrimination (both at glomeruli and mitral/tufted)
Lateral inhibition
Via CN1 (olfactory nerve), mitral/tufted cells connected to a ____ show distinct patterns of projections to several areas of the olfactory cortex
single glomerulus
For olfactory projections, the mitral valve sends info to how many regions and what are they?
Sends info to 5 regions
1. ant olf. nucleus
2. olf. tubercle
3. piriform cortex
4. amygdala
5. entorhinal cortex
For olfactory projetions, what is the pathway responsible for odor perception and discrimination?
The pathway through the thalamus to the orbiotfrontal cortex
The pathways to the amygdala and hypothalamus is resppnsible for what aspects of smell?
Emotional and motivational aspects of smell
Physiological and behavioral aspects of smell
What is responsible for odor induced fear signaling?
Amygdala-piriform boundary
Order of olfactory system
Olfactory epith
olfactory bulb
olfactory cortex
this system is a network that contributes ti the summation of distinguishing smells
Olfactory impairment is a side effect of which diseases?
Parkinsons, Huntigtions, Alzheimers, Covid
Olfactory senescence begins at what age and involved the loss of smelling what type of odors?
Age 36 and involves the loss of smelling pleasant odors
Where are taste cell receptors located?
On the tongue, pharynx, palate, epiglottis, upper 3rd of the esophagus
NOT NEURONS
Which CN innervate the gustatory system?:
VII, IX, X
CN VII (chorda tympani branch of facial) innervates via what?
Geniculate ganglion
innervates tongue
CN IX (lingual branch of the glossopharyngeal) innervates via what?
Petrosal ganglion
innv tongue
CNX (sup laryngeal branch of vagal) innervates via what?
Nodose ganglion
does not inn tongue, it does pharynx, etc
Taste buds (containg taste cells) of the tongue are embedded where?
Papillae of the tongue
What innervates the anterior 2/3 of the tongue and what type of papillae can we find here?:
Inn by CNVII (chordi a tympani/facial)
You can find fungiform & filiform papillae
What innervates the posterior portion of the tongue and what type of papillae can we find here?:
Inn by CN IX (glossopharyngeal)
can find circumvallate and foliate papillae
What are the tastants and what molecules are responsible for them?
- Sweet-sucrose (threshold 20mM)
- Salty-NaCl (threshold 10mM)
- Sour-Citric acid (threshold 2mM)
- Bitter- quinine (threshold 8microM)
- Umami-glutamate (threshold 100microM)
- Water
Specific taste occurs where?
across the whole tongue, just @ diff amounts
What are the diff types of taste cells that we have?
Type 1,2,3, basal cells
type 1> type 2> type 3
Type 1 cells
Support fxn
Putative (tentative) salt sensor
type 1> type 2> type 3
Type 2 cells
- Contain the GPCRs signaling effectors for bitter, sweet and umami
- Associate closely w/ afferent nerve fibers; DO NOT form conventional synapses
type 1> type 2> type 2
Type 3 cells
- Respond to sour stimuli
- form prominent synapses with afferent nerve fibers
- Vesicular release of serotonin and ATP
type 1> type 2> type 2
Basal cells
progenitor cells (10 day turnover rate)
Type 2 cells respond to what type of tastant stimuli?
Umami, sweet, and bitter
Umami has what type of receptor? Made up of what proteins?
type 2 cell
1 T heterodimer GPCR
proteins: T1R1 + T1R3
need to have both activated in order to have activation of GPCR
Sweet has what type of receptor? Made up of what proteins?
1 T heterodimer GPCR
Protein: T1R2 + T1R3
expressed in T1R2 and 3
Bitter has what type of receptor?
30 T2Rs
Monomor GPCR
mediated by T2 receptor family
Type 1 cells respond to which taste stimuli?
Sodium
What is the receptor for sodium?
ENaC
ion channel
Type 3 cells responds to what taste stimuli?
Sour and carbonation cells
ion channel
What is the receptor for sour?
PKD2L1
Sour is a sensation caused by ____ acidification of type ____ cells (membrane permeable acids are more potent tastants)
Intracellular, 3
not gpcr
Explain type 2 signal transduction
- Sweet/umami/bitter enters ton gue and binds to GPCR taste receptor
- G. gustucin (like a gq)
- PLP C is activated, IP3 activates, and causes release of Ca2+ from ER.
- TRPM5 channel is now activated and allows Na+ rushing in causing dep and ap
- CALMH1 channel is now activated and allows ATP to flow out activating the nerve. (its a NT pore)
CALHMI: calcium homeostasis modulator 1 (voltage -gated channel)
High sensitivity salty taste is at high or low concentration of salt?
Low
High salt sensitivity is responsible for salt ____. Via what?
salt attraction via epitheliali sodoum channel (ENaC)
Salt attraction is sensitive to?
a. NaCL only
b. KCL and CsCl only
c. All of the above
NaCl only
Salt attraction is inhibited by what?
Amiloride
are type 1 cells responsible for salt aversion?
NO, type 2 cells are
Low sensitivity salty taste is at high or low concentration of salt?
high
Low salt sensitivity is responsible for salt ____. Via what:?
aversion, bia bitter receptors on type 2 cells
Salt aversion is sensitive to?
a. NaCL only
b. KCL and CsCl only
c. All of the above
all of the above
What type of expressing cells are critical for sour sensing?
PKD2L1
Citric acid (sour) induces cation influx via what?
PKD heterodimer
Does PKD knock out eliminate sour sensing?
NO, only reduces
What are the two types of afferent nerves/fibers associated with taste cells:?
Intragemmal fiber (gustatory nerves)
Perimeggmal fibers (somatosensory nerves)
What are the gustatory nerves that innervate taste bud/cell
CN VII, IX, X
Gustatory nerves contain what type of receptor that is critical for all tastes?:
G-gustucin-P2X2/3
atp sensitive ion channel
gettting rid of ATP pathway (which activates these nerves, you gt rid of nerve acitvation
What is the somatosensory nerve that play a role in chemesthesis?
CN V (trigeminal)
Communication between TC and afferent nerve requires ____ and ____ ion channels
purinergic, serotnergic
if you were to ko purinergic channel ATP channels, you wipe out sensitivity of nerve
For Intragemeal fibers (gustatory nerves), type 2 cells release ATP via what?
Via CalHM1 (non vesicle)
For Intragemeal fibers (gustatory nerves), type 3 cells release ATP and 5-HT via what?
via vesicles
What is the enzyme that breaks down ATP signals?
NTPDase
Possible inter TRC communication is due to cross talk with which molecules?
ATP, GABA, and 5HT
inter-TRC communication
Activated Type 2 cells release ATP which does what to Type 3 cells
activates Type 3 cells
Activated Type 3 cells release GABA and 5HT which does what to Type 2 cells
inhibits Type 2 cells
In the somatosensory system, we have many trigemminal nerves in the tongue and these are perigemmal fibers. Are these perigemmmal fibers interacting with taste cells?
NO, they free nerve endings that detect aversive stimuli (pain) and temp in the oral cavity (chemesthesis)
senses pungencey not taste
What ate the nociceptors subtypes for the perigemmal fibers?
TRPV1: chili (capsaicin), heat, acid
TRPA1: wasabi
TRPM8: menthol, cold
Perigemmal fibers have CNS projections to the ____ in the medulla and onto the thalamus to modulate taste and in some cases, evoke ____.
Sp5, defensive reflexes
Projections of the various gustatory nerves travel to the cortex via
- Nucleus of the solitary tract (NST) in the medulla
- NST cells send fibers to cortex via ventral posterior medial thalamus (VPM) and the parabrachial nuc (PbN)
- In the gustatory nuc (GN) of the cortex, info is sep from other sensory modalities of the tongue
What are the 3 types of info extracted from tastants?
Quality, intensity, hedonic value
What does quality of a tastant mean?
Is it salty, sweet, etc
What does intensity of a tastant mean?
How sweet is it, how salty is it, etc
What does hedonic value of a tastant mean?
Perceived pleasantness or unpleasantness of a stimulus
can be measured by ingestive vs protective behaviors
In the CNS there is is an ____ of neuronal responses such as sweet, salt, and sour, but none between _____.
overlap, bitter and sweet
no structural differance, they oppose each each other (salty and sour don’t have opposites)
Stimuli such as sweet, salty, etc cause motor driven behaviors that result in ____ or ____ responses.
ingestive, protective
ingestive: tongue protrusions, salivation, insulin release, swallign
protective: gapes, chin rubbing, coughing, apnea, salivation
