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Neuroscience Exam 2 > Lecture 1: Olfaction and Taste > Flashcards

Lecture 1: Olfaction and Taste Flashcards

1
Q

How many olfactory stimuli can humans discriminate?

A

over 1 trillion

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2
Q

Where are olfactory cells located?

A

in the epithelium of the nose

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3
Q

What are the physical characteristics of olfactory receptor neurons?

A
  • Bipolar cells
  • Dendrites form the cilia
  • Axons terminate in olfactory bulb
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4
Q

Where do the olfactory neurons project its axon?

A

Through cribriform bone into the olfactory bulb, then synapse with central nervous system neurons and project to different brain parts.

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5
Q

What type of molecules do odorants tend to be?

A

Small volatile molecules that are lipid soluble

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6
Q

~400-500 genes in the human genome code for how many olfactory receptors?

A

~1000

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7
Q

Odor receptors have how many transmembrane domains?

A

7

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8
Q

What type of receptors (GPCR or ligand-gated) are odorant receptors?

A

G protein coupled-receptor (GPCR)

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9
Q

Odor receptors detect odorants based on what? (4)

A
  • Size
  • charge
  • amino acid group
  • vibration of C-H groups
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10
Q

Where is the location of the binding site of odor receptors?

A

on extracellular terminus

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11
Q

Each neuron has _____ type of receptor but can respond to more than one __________.

A

one, odorant

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12
Q

A single odor receptor may respond to ___________ or ________odorants

A

Single, Multiple

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13
Q

What is the 1st route of activation of the release of the olfactory G-protein (GOLF)?

A
  1. Activates adenylate cyclase→produces cAMP
  2. cAMP opens Cyclic nucleotide-gated channel (CNGA) →Na+/Ca2+ influx (depolarization)
  3. Ca2+ activates Cl- channel →Cl- efflux (further depolarization)
  4. Depolarization triggers action potentials
  5. Ca2+ levels are restored by exchangers (Na+/Ca2= exchanger) and pumps
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14
Q

What steps are involved in reducing odorant sensitivity?

Olfactory Adaptation

A
  1. All steps from 1st route of activation of GOLF2.
  2. Inititial adaptation-occurs when increased Ca2+ binds to Ca2+ binding protein that desensitizes CNGA channel
  3. Short term adaptation-occurs by increased desensitization via Ca2+ calmodulin protein kinase 2 acting on adenylyl cyclase
  4. Long term adaptation-occurs downstream of Ca2+ mediated nitric oxide production -> stimulates guanylate cyclase to produce cGMP and causes Ca2+ influx through CNGA channel; leading to desensitization of CNGA and adenylyl cyclase
  5. a Na+/Ca2+ exchanger restores ionic balance
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15
Q

What is the 2nd route of the olfactory receptor via the release of GOLF?

A
  1. activates phospholipase C (PLC)-IP3 pathway -> opens Ca2+ channel
  2. Ca2+ channel causes desensitization
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16
Q

What occurs during Olfactory Adaptation?

A

Reduction in odorant sensitivity

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17
Q

Explain the Initial Adaptation that occurs during olfactory adaptation

A

Occurs when increased Ca2+ binds to cbp (Ca2+ binding protein) that desensitizes the CNGA channel

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18
Q

Explain the Short-term Adaptation that occurs during olfactory adaptation

A

Occurs by increased desensitization of Ca2+ calmodulin protein kinase II acting on AC (adenylate cyclase) which decreases the production of cAMP

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19
Q

Explain the Long-term Adaptation that occurs during olfactory adaptation

A
  • Occurs downstream of Ca2+ mediated nitric oxide production which stimulates guanylate cyclase to produce cGMP (cG)
  • cGMP causes persistent Ca2+ influx through the CNGA channel. leading to further desensitization of CNGA and AC
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20
Q

What is the purpose of the vomeronasal organ in non-ape mammals?

A

To mediate activation by pheromones

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21
Q

What organ is considered a high specialist receptor?

A

vomeronasal

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22
Q

What are the (4) characteristics of the 2nd group (TAARs) of chemosensors in olfactory epithelium? (TAARs: Trace-Amine-Associated Receptors)

A
  • Found in all mammals including humans
  • Highly selective for specific pheromones
  • Highly sensitive
  • Uses GOLF/cAMP signal transduction mechanisms
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23
Q

What is a glomerulus?

A

Axon of the olfactory receptor neurons in the glomeruli of the olfactory bulb (~2000 glomeruli in mammals)

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24
Q

Each glomerulus receives info from what?

A

only one type of olfactory receptor neuron

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25
Each glomerulus receives thousands of olfactory receptor neuron axons which synapse with what?
20-50 relay neurons (mitral/tufted) ## Footnote Similar/identical OR (odordant receptor) to the same glomerulus
26
Where does olfactory info from the PNS enter the CNS?
glomerulus
27
What are the 5 layers of the olfactory bulb?
1. Olfactory receptor nerves 2. Odorant-specific glomeruli (synapses) 3. External plexiform layer 4. Mitral cell layer 5. Granule cell layer
28
Tufted/mitral cells receive info from __________ and relay info to _________
olfactory sensory neurons in the glomerulus; olfactory tract (CNS)
29
What is the purpose of parallel projection involved in lateral inhibition?
increases odor discrimination (both @ glomeruli and mitral/tufted)
30
What is an example of lateral inhibition?
If the green odorant has a large activation and the blue odorant has partial activation, green will shut down blue, and only green will be presented
31
What cranial nerve does olfactory projection go through?
Cranial nerve I (Olfactory nerve)
32
Mitral cells send info to how many different regions? And list them?
**5**, Info goes through the lateral olfactory tract and then to either: * Anterior olfactory nucleus * Olfactory tubercle * Piriform cortex * Amygdala * Entorhinal cortex
33
Where do tufted cells send information to?
* Anterior olfactory nucleus * Olfactory tubercle
34
What pathway is responsible for odor perception and discrimination?
thalamus to the orbitofrontal cortex
35
Pathways to the amygdala and hypothalamus regulate what?
* Emotional/motivational aspects of smell * Physiological/behavioral aspects of odors
36
Odor-induced fear signaling is located in what boundary?
amygdala-piriform
37
What cortex lacks structure/organization?
piriform
38
At what age do humans begin to lose the smell of pleasant odors? ## Footnote Olfactory Senescence
36
39
How is olfaction related to Idiopathic Parkinson's Disease?
* Show more loss of smell than Vascular Parkinson's * Tend to be anosmic (loss of smell)
40
How is olfaction related to Huntington's Chorea?
Pts show an intermediate amount of olfaction loss
41
How is olfaction related to Alzheimer's Disease?
Have olfactory impairment that may begin centrally
42
SARS-Cov-2 likely infects what cells to express what?
support cells in olfactory epithelium -> express ACE2
43
Where are taste cells located?
* Tongue * Pharynx * Palate * Epiglottis * Upper third of the esophagus
44
The gustatory system is innervated by what nerves?
* CN VII (7)-Facial * CN IX (9)-Glossopharyngeal * CN X (10)-Vagus
45
What are the characteristics (name and innervation) of cranial nerve VII?
* Facial (chorda tympani branch) via geniculate ganglion * Innervates the tongue
46
What are the characteristics (name and innervation) of cranial nerve IX?
* Glossopharyngeal (lingual branch) via petrosal ganglion * Innervates the tongue
47
What are the characteristics (name and innervation) of cranial nerve X?
* Vagal (superior laryngeal branch) via nodose ganglion * Innvervates the pharynx and esophagus
48
Taste buds on the tongue are embedded in what?
papillae
49
What is located at the anterior 2/3 portion of the tongue? And what innervates it?
* fungiform and filiform papillae * Innervated by the facial nerve (CN VII)
50
What is located at the posterior portion of the tongue? And what innervates it?
* Circumvallate and foliate papillae * Innervated by the glossopharyngeal nerve (CN IX)
51
How many taste buds are on the human tongue?
4000
52
What occurs at the apical end of the tongue?
Microvilli contact the tastant which is dissolved in saliva and tastes pore mucus
53
How often does the turnover of taste cells occur?
every 10 days
54
What are the tastants?
* **Sweet** →sucrose (threshold 20 mM) * **Salty** → NaCl (threshold 10 mM) * **Sour** →citric acid (threshold 2 mM) * **Bitter** →quinine (threshold 8 𝜐M) * **Umami** → glutamate (meaty flavor) (threshold 100 𝜐M) * Water
55
What are the 4 types of taste cells?
* Type I * Type II * Type II * B cells
56
What is the purpose of type 1 taste cells?
Have support function → putative salt sensor
57
What are the characteristics of type 2 taste cells?
* Large cells that have GPCRs for bitter, sweet, and umami * Associate with different afferent nerve fibers * DO NOT form conventional synapses
58
What are the characteristics of type 3 taste cells?
* Respond to sour stimuli * Form prominent synapses with afferent nerve fibers * Vesicular relase of serotonin and ATP * HAVE conventional synapses
59
What type of cells are B cells?
progenitor cells
60
What is the numerical distribution of the taste cells?
type 1> type 2> type 3
61
What is the taste receptor associated with umami?
T1R1 + T1R3
62
What is the taste receptor associated with sweetness?
T1R2 + T1R3
63
What is the taste receptor associated with bitterness?
~30 T2Rs
64
What is the taste receptor associated with sodium?
ENaC (Epithelial sodium channels)
65
What is the taste receptor associated with sour?
* PKD2L1 for acids * CA IV for carbonated drinks
66
What are the steps involved in type 2 signal transduction for taste?
1. Tastant binds to the receptor on the outside of the membrane 2. Stimulates Ggustucin (Gq) →activates phospholipase CB2 (PLCB2) 3. Hydrolysis of PLCB2 into IP3 and DAG 4. IP3 binds to endoplasmic reticulum→Ca2+ releases 5. Ca2+ activates TRPM5 Na+ permeable channel→Na+ influx (depolarization) 6. Na+ gated channels open→Na+ influx causes a burst of action potentials 7. Depolarization activates CALHM1 (NT pore)→ATP flows out and activates nerve | CALHM1:Calcium homeostasis modulator 1 (voltage-gated channel) ## Footnote Remember Type II DO NOT form convential synapses
67
High sensitivity via epithelial sodium channels (ENaC) is responsible for what? ## Footnote
* Salt attraction (lower conc. of salt) * NaCl sensitive-not KCl or CsCl
68
Low sensitivity via epithelial sodium channels (ENaC) is responsible for what?
* Salt aversion via bitter receptors (high conc. of salt) * All salts sensitive
69
High sensitivity/low concentration for salt occurs in what type of cells?
Type 1
70
Low sensitivity/high concentration for salt occurs in what type of cells?
Type 2 via bitter receptors
71
For high sensitivity, what is salt attraction inhibited by?
amiloride
72
What cells are critical for sour sensing?
PKD2L1-expressing cells (Type III)
73
How does citric acid induce cation influx?
via PKD heteromer
74
How can sour sensing be reduced?
PKD knockout ## Footnote Reduces sour sensing, not eliminate
75
Which fibers play a role in communication between taste cells and afferent nerves?
* Intragemmal Fibers (inside taste buds) * Perigemmal Fibers (outside taste buds)
76
What type of nerves are intragemmal fibers? and what do they contain?
* Gustatory Nerves * CN VII, IX, X-innervate taste bud/cell * Contain P2X2/3 receptors (critical for all tastes) ## Footnote P2X2/3 (ATP sensitive ion channel)
77
What type of nerves are Perigemmal fibers? and where do they play a role?
* Somatosensensory Nerves * CN V (Trigeminal) * Play a role in chemesthesis (chemical sensitivity of the skin and mucous membranes)
78
Communication between taste cells and afferent nerves requires _______ and _______ ion channels
Purinergic (P2X2/3); Serotonergic (5HT3)
79
How important are Purinergic (P2X2/3) and Serotonergic (5HT3) ion channels?
* Purinergic (P2X2/3)-critical for all tastes (very imp.) * Serotonergic (5HT3)-minor contribution
80
ATP is important for communication between the taste cells and afferent nerves. How is it released in taste cells?
* Type 2: ATP via CalHM1 (non-vesicle) * Type 3: ATP and 5HT (via vesicles) ## Footnote Type I role not fully understood
81
During the communication between taste cells and afferent nerves, what occurs in the synapse?
* NTPDase 2 breaks down ATP signals * ATP, GABA, and 5HT cause inter-TRC communication
82
During the communication between taste cells and afferent nerves, how do type 2 cells indirectly activate type 3 cells?
by releasing ATP
83
During the communication between taste cells and afferent nerves, activated type 3 cells release what to inhibit type 2 cells?
GABA and 5HT
84
What are each taste cells innervated by?
Primary gustatory fibers (CN VII, IX, and X) ## Footnote * Each fiber branches, innervating many taste buds and many taste cells within a bud * Electrical activity within a single fiber represents input from many cells
85
What are specialist afferent fibers?
* Labeled-line coding-specific tastes * Type 2 cells
86
What are generalist afferent fibers?
* Combinatorial coding- multiple tastes * Type 3 cells
87
How do gustatory nerves travel to the cortex?
1. Solitary tract to **nucleus of solitary tract (NST)** in the **medulla** 2. NST cells send fibers via **ventral posterior medial thalamus (VPM)** and the **parabrachial nucleus (PbN)** 3. Info for taste is separated from other senses in the **gustatory nucleus (GN)** of the cortex
88
What are the 3 types of information extracted from tastants?
1. Quality (is it salty? is it sweet) 2. Intensity (how sweet is it? how salty is it) 3. Hedonic (pleasantness/unpleasantness)- measured by ingestive vs protective response
89
What are Ingestive Behaviors?
* Tongue protrusions * Salivation * Insulin release * Swallowing
90
What are Protective Behaviors of taste?
* Gapes * Chin rubbing * Coughing * Apnea * Salivation
91
In the CNS, what neuronal responses overlap?
sweet, salty, and sour (NOT bitter and sweet)
92
Tastant stimuli cause what? What's the result?
motor-driven behaviors that result in ingestive/protective responses
93
What nerves innervate the oral cavity?
trigeminal sensory nerves
94
What is the main somatosensory innervation of the head?
Trigeminal (CN V)
95
Perigemmal Fibers do NOT interact with taste cells. What do they interact with?
* Aversive stimuli (i.e. pain) * Temperature in the oral cavity (chemesthesis)
96
What are the subtypes in chemesthesis?
mechanosensors and nociceptors
97
What are the Nociceptors subtype and what types of temperatures do they express?
* **TRPV1**: chili, heat, acid * **TRPA1**: wasabi * **TRPM8**: menthol, cold
98
What is the temperature expressed by nociceptor TRPV1?
Chili, heat, and acid
99
What is the temperature expressed by nociceptor TRPA1?
Wasabi
100
What is the temperature expressed by nociceptor TRPM8?
Menthol, cold
101
All of the following are true regarding olfactory receptors EXCEPT: a. Olfactory receptors consist of 7 trans-membrane domains b. TAAR’s are highly selective for specific pheromones c. A single olfactory receptor nerve can only respond to a single odorant d. The vomeronasal organ contains specialist receptors in non-ape mammals
c. A single olfactory receptor nerve can only respond to a single odorant
102
Olfactory adaptation exerts its influence on almost all aspects of the functioning of the sense of smell. Which of the following mediates short-term olfactory adaptation? a. Increased Ca2+ binding to Ca2+ binding protein (cbp) b. Calmodulin protein kinase II (CaMKII) acting on adenylate cyclase c. Ca2+-mediated nitric oxide production d. Increased cGMP production causes persistent Ca2+ influx via CNGA
b. Calmodulin protein kinase II (CaMKII) acting on adenylate cyclase
103
Taste receptors can be found in small structures known as papillae throughout the tongue and innervated according to their specific location. Which of the following is correctly paired? a. CN VII; Petrosal ganglion; Foliate papillae b.CN IX; Petrosal ganglion; Filiform papillae c. CN VII; Geniculate ganglion; Fungiform papillae d. CN IX; Geniculate ganglion; Circumvallate papillae
c. CN VII; Geniculate ganglion; Fungiform papillae
104
Which of the following mammalian taste cells and receptors are responsible for sensing sweet tastants (i.e. artificial sweeteners)? a. Type II cells w/ T1R2 + T1R3 b.Type III cells w/ PKD2L1 c. Type II cells w/ T1R1 + T1R3 d. Type I cells w/ ENaC
a. Type II cells w/ T1R2 + T1R3
105
Projections of the various gustatory nerves (i.e. CN VII, IX, & X) travel to the cortex via which of the following tracts? a. GN→NST→VPM b.VPM→NST→GN c. NST→GN→VPM d. NST→VPM→GN
d. NST→VPM→GN

Neuroscience Exam 2 (9 decks)

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