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Neurobiology > Taste And Olfaction > Flashcards

Taste And Olfaction Flashcards

0
Q

How is olfaction sensed ?

A

By chemoreceptors

Sensation form air borne odourants/volatiles

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1
Q

How is taste sensed ?

A

By chemoreceptors

Sensation from hydrophilic substances dissolving in saliva

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2
Q

What behaviours do taste and smell play a role in ?

A 
Feeding 
Parenting 
Mating 
Altering
Territorial behaviour
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3
Q

What is the dominant sense in humans ?

A

Vision

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4
Q

What is hypogeusia and ageusia ?

A 
Hypogeusia= reduced ability to taste 
Ageusia = inability to taste
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5
Q

What is hyposmia and anosmia ?

A 
Hyposmia= reduced ability to smell or detect odours 
Anosmia= inability to detect odours
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6
Q

What are the detection threshold holds for salt, sugar, acids and alkaloids ?

A

Salt - 10mM
Sugar- 20mM
Acids- 0.01mM
Alkaloids - 0.0001mM

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7
Q

What are the 5 basic tastes ?

A 
Sweet
Bitter 
Sour 
Salty 
Savoury - umami
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8
Q

Why is spicy or minty not classified as a taste ?

A

Because they are not detected by taste receptors, they are classed as somatosensory responses

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9
Q

Other than taste what other factors contribute to taste sensation ?

A

Visual aspect of food, smell of food and also texture of food

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10
Q

What are the 3 different papillae ?

A

Circumvallate, foliate and fungiform

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11
Q

Describe circumvallate papillae

A

Largest- many thousands

Located at the posterior of the tongue

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12
Q

Describe foliate papillae

A

Contain many hundreds of taste buds

Elongated structure along the lateral posterior edge of tongue

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13
Q

Describe fungiform papillae

A

Smallest contain 1 to 2 taste buds

Widespread across anterior surface of the tongue

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14
Q

What are taste buds like ?

A

Garlic clove shaped - 30 micrometers
Contain about 50-60 cells
Have microvilli to project into taste pore
Lifespan of about 2 weeks - replenished by basal cells

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15
Q

How do tastants trigger a transduction cascade ?

A

Direct pass through ion channels - salty and sour because you have cations which can pass through
Bind to and block ion channels
Bind to be open ion channels
Bind to receptors and activate a 2nd messenger system to modulate ion channels

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16
Q

Why are taste buds not true neurons ?

A

Because they not have an axon

17
Q

Why is the highest sensitivity on the tongue for bitter tastes ?

A

Posterior

18
Q

Where is there higher sensitivity for sweet taste on the tongue ?

A

Tip of the tongue

19
Q

Describe the sensory transduction of taste receptor cell

A

Dissolved molecules bind to sites or ion channel modulation in apical microvilli
Trigger membrane depolarisation and increase AP firing
Accompanied by increas I’m intracellular calcium which cause nt release
Released onto afferent nerves 7,9,10

20
Q

Where do nerves 7, 9 and 10 receive their innervation from ?

A

7- anterior 2/3 of tongue
9- posterior 1/3 of tongue
10- epiglottis

21
Q

What is the transduction cascade for salty tastants ?

A

Salty food increases sodium concentration which passes down concentration gradient through amiloride sensitive sodium channels
This depolarises the cell causing calcium influx and therefore nt release

22
Q

What is the transduction cascade for sour tastants ??

A

Sourness is a reflection of acidity
He increased proton concentration passes through amiloride sensitive sodium channels causing depolarisation and they also block potassium channels helping to contribute to depolarisation

23
Q

What is the transduction cascade for bitter tastants ?

A

Bind to specific T2R gpcr
Increases PLC
Increases IP3
IP3 triggers opening of TRPM5 channels allowing calcium inflict and therefore nt release
Also activates sodium channels causing calcium release from intracellular stores

24
Q

What is the transduction cascade for sweet tastants ?

A 
Bind to T1R gpcr (T1R2 and T1R3 complex) 
Activates PLC 
Increases IP3 
Causing sodium influx 
Same as bitterness
25
Q

What is the transduction cascade for umami tastants ?

A

Identical to sweet but the receptor complex is T1R1 and T1R3 Instead

26
Q

What are the 2 families of GPCRs used in detecting taste?

A

T1R and T2R

27
Q

Explain the central gustatory pathway ?

A

1st order neurons project to gustatory nucleus in the nucleus of the solitarius in the medulla
2nd order neurons project to the ventral posterior medial nucleus of the thalamus
3rd order neurons projects to guststory cortex= insula, operculum and postcentral Gyrus

28
Q

What are the functions each of these structures in taste ?

  • cortex
  • hypothalamus
  • amygdala
A

Cortex is involved in perception
Hypothalamus is involved in appetite and saiety
Amygdala is involved in pleasure and avoidance

29
Q

What are the stimuli for olfaction ?

A 
Airborne molecules 
Alcohols 
Esters 
Aromatics 
Long chain fatty acids 
Muses 
Pheromones
30
Q

What percentage of human genome are involved with olfaction ?

A

3%

31
Q

What is the difference between threshold values to perceive odors between lipid soluble and water soluble odourants ?

A

Lipid soluble have low thresholds while water soluble have high thresholds

32
Q

What are the 3 main cell types involved in olfaction ?

A

Olfactory receptors - site of transduction
Supporting cells - secrete mucus
Basal cells - replace receptors

33
Q

What are the sequence of events in the olfaction cascade ?

A 
Odourants bind to receptors on cilia 
Activate GPCR
Increases cAMP 
cAMP opens sodium and calcium channels 
Chloride channels opened 
Depolarisation
34
Q

What is the receptor potential like in cilia ?

A

It generates slow membrane potential depolarisations

35
Q

What are the main receptor groups of olfactory receptors ?

A 
Odourants receptors (ORs) 
Vomeronasal receptors (V1Rs and V2Rs) 
Trace-amine associate receptors (TAARs) 
Formyl peptide receptors (FPRs) 
Guanyl cycles receptors (GC-R)
36
Q

How are olfactory receptors distributed in the olfactory epithelium ?

A

Distributed heterogenously across olfactory compartments
Specific groups of receptors are most dense in separate non overlapping zones
- within the zone difference receptors of that group are randomly distributed

37
Q

Describe the specificity of olfactory receptor cells

A

Cells express only 1 type of receptor

Each has a particular response profile to odourants

38
Q

How many endings of first order neurons does the glomerular receive ?

A

25K

39
Q

What does the glomerulus do ?

A

Converges the 25k 1st order neurons onto 100 2nd order neurons

40
Q

What are the direct targets of the olfactory tract ?

A

Olfactory cortex
Amygdala - motivation/pleasure
Entorhinal cortex
Olfactory tubercle

41
Q

What are the indirect targets of the olfactory tract ?

A

Thalamus - gateway to neocortex
Neocortex - perception
Hippocampus - learning and memory
Hypothalamus - feeding/ fasting

Neurobiology (30 decks)

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