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MVST1B NHB > Olfaction and taste > Flashcards

Olfaction and taste Flashcards

1
Q

Airborne odorants are detected by the……. in the nasal cavity

A

Airborne odorants are detected by the olfactory epithelium in the nasal cavity

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2
Q

in order to be detected, musst odourants dissolve in themucus fil,m?

A

yes

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3
Q

Olfactory receptors are renewed every ___ days by basal cell division.

A

Olfactory receptors are renewed every 60 days by basal cell division.

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4
Q

humans have about ___ odour receptro genes

A

350

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5
Q

describe hwo transduction takes place in the olfactory cilia

A
  • odour interacts with receptor
  • recetpor activates G(ofl) protein
  • stimates Adenylyl cyclase
  • produces cAMP
  • opens cyclic nucleotide-gated cation channels in the ciliary membrane
  • inwards flowing receptor current - Ca2+ and Na+
  • ca2+ opens CL- channels (augmenting response)
  • The receptor current increases with odorant concentration, increasing spike firing
  • The Ca2+ that enters is principally extruded by sodium-calcium exchange, but Ca-ATPase may contribute in some species.
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6
Q

how does calcium modulate sensitivity of olfactory receptors?

A

Ca also acts via calmodulin to reduce the sensitivity of the cation channels to cAMP

contributing to olfactory adaptation

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7
Q

is the receptor current proportional to the odour concentration?

A

yes

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8
Q

increasing the receptor current has what effect on spike firing?

A

increasing receptor current increases spike firing

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9
Q

what does this show?

A

graded receptor current

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10
Q

graphically how does increasing odour concentration alter the trains of spike firing?

A
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11
Q

Olfactory receptor axons pass through the …… to the olfactory bulb.

A

Olfactory receptor axons pass through the cribriform plate to the olfactory bulb.

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12
Q

Olfactory receptor axons pass through the cribriform plate to the olfactory bulb. There they excite ,…. which cells?

A

Olfactory receptor axons pass through the cribriform plate to the olfactory bulb. There they excite mitral cells and smaller tufted cells in the olfactory glomeruli.

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13
Q
A
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14
Q

whats the role of Periglomerular cells and granule cells in the olfactory bulb?

A

Periglomerular cells and granule cells make reciprocal dendro-dendritic synapses with mitral cells, mediating lateral inhibition which may sharpen mitral cell odour tuning

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15
Q

howa re odours represented in the bulb?

A

Different odorants evoke distinct, but overlapping activity patterns in the bulb.

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16
Q

does the spacial positiob of the axons in the olfactory tract have any meaning?

A

no - constrast with vision

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17
Q

odours are coded by combinatory code?

A

true

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18
Q

does lateral inhibition sharpen odour tuning?

A

yes

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19
Q

what does the anterior olfactory nucleus do?

A

The anterior olfactory nucleus mediates inhibition between the two bulbs via the anterior commissure.

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20
Q

what do mitral cell axons do?

A

Mitral cell axons leave the bulb in the lateral olfactory tract.

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21
Q
A
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22
Q

do humans smell in stereo?

A

some evidence to suggest we do! recelty

might have t ogoogle what it actually is though - good for essay conent

23
Q

The lateral olfactory tract synapses on neurons in five regions of olfactory cortex.

what are they?

A
  1. Anterior olfactory nucleus
  2. Olfactory tubercle
  3. Pyrtiform cortex
  4. Amygdala
  5. and entorhinal cortex
24
Q
A
25
Q

what does this suggest?

A

At higher levels in the pathway cells become progressively more odour-specific: the majority of cells in the bulb respond to many odorants, while those in orbitofrontal cortex mostly respond to just one or two.

26
Q

whast the vomeronasal organ do?

A

The vomeronasal organ projects via the accessory olfactory bulb to the amygdala to mediate the responses to pheromones involved in sexual and social behaviours in some species.

MHC peptides may also function as social recognition signals. In humans, Trace Amine Associated Receptors in the main olfactory epithelium may detect volatile amines in sweat to shift mood and perhaps increase fertility.

27
Q

T or F

humans don’t have a vomeronasal organ

A

T

Trace Amine Associated Receptors in the main olfactory epithelium may detect volatile amines in male human sweat…

28
Q

is taste as diverse as smell?

A

no

29
Q

Taste receptor cells are clustered together in___ _____, which are located in…

A

Taste receptor cells are clustered together in taste buds, which are located in papillae embedded in the epithelium of the tongue.

30
Q

3 classes of papillae?

A

These can be classified into circumvallate, foliate and fungiform papillae.

31
Q
A
32
Q

Receptors in the taste buds of the tongue synapse with afferent fibres projecting in the _____ ____ ______nerves.

Taste buds on the epiglottis project via the ____ ______nerve.

A

Receptors in the taste buds of the tongue synapse with afferent fibres projecting in the chorda tympani and glossopharyngeal nerves.

Taste buds on the epiglottis project via the superior laryngeal nerve.

33
Q
A
34
Q

do taste receptor cells (presynatpic cells) have to fire APS?

A

no - theyr short recpetors

35
Q

5 taste qualitites

A

Human taste transduction involves four classical taste qualities, bitter, sweet, sour and salt, and a fifth called umami: the taste of glutamate.

36
Q

umami us the taste of?

A

glutamate

37
Q

which classsic tastes involve specific receptor proteins acting vis second messengers?

A

bitter sweet and umami

38
Q

how are salt and sour tastes modulated?

A

Sour and salt responses are mediated more directly by modulation of ion channels in the taste cell surface membrane.

39
Q

3 classes of taste cells?

A

Receptor cells have narrow specificity, expressing receptors for bitter, sweet or umami.

Presynaptic cells, respond directly to acid stimuli.

Glial-like cells carry out potassium and transmitter homeostasis, and may participate in salt transduction.

40
Q
A
41
Q

Heterodimeric receptors coupled to a G protein underlie the umami (____+____) and sweet (____+______) responses.

Bitter responses are sensed by a family of around 30 ______ receptors, which may also dimerise, whose number may account for the molecular diversity of bitter compounds.

A

Heterodimeric receptors coupled to a G protein underlie the umami (T1R1+T1R3) and sweet (T1R2+T1R3) responses. Bitter responses are sensed by a family of around 30 T2R receptors, which may also dimerise, whose number may account for the molecular diversity of bitter compounds.

42
Q

do bitter receptors respond t odangerous plant alkaloids?

A

yes - hence why theres 30

43
Q

describe the process of taste transduction in umami, sweet adn bitter receptors

A

The ligand-bound receptor molecules then activate a G protein,

whose beta and gamma subunits stimulate production of IP3,

leading to Ca2+ release from intracellular stores,

and the opening of TRP5M cation channels.

The elevated Ca2+ concentration and the accompanying depolarisation lead to transmitter release from receptor cells via gap junction hemichannels.

44
Q
A
45
Q

describe the mechanism of sour taste trasduction

A

Sour transduction involves intracellular acidification by a weak acid. The mechanism is not fully understood, but appears to involve a potassium channel which is blocked by intracellular protons, leading to depolarization, the opening of Ca2+ channels and vesicular transmitter release from presynaptic cells.

46
Q

describe how salt transuction occurs

A

Salt transduction involves the entry of sodium ions through epithelial sodium leak channels, depolarizing glial-like cells. Protons can also enter via these channels.

47
Q

Taste afferents in the chorda tympani, glossopharyngeal and superior laryngeal nerves proceed via cranial nerves VII, IX and X to synapse in the…….

A

synapse in the solitary nuclear complex of the medulla within the gustatory nucleus.

In the primate, an uncrossed pathway projects to the ventral posterior medial nucleus of the thalamus, and thence to gustatory neocortex in the anterior insula and frontal operculum.

48
Q
A
49
Q

From primary taste cortex, projections pass to

the secondary taste areas …….

(3)

A

oribitofrontal cortex:

here units modulate their discharge according to the pleasantness of the taste of food

Amygdala:

plays a role in the affective component of teh taste - seek more? - motivation component

lateral hypthalamus:

modulates feeding behaviour

50
Q

describe whats emant by an across fibre code regarding taste encoding?

A

recordings from afferents in the chorda typani show that individual fibres respond to a range of stimuli, but tend to prefer just one of these. This indicates instead an across-fibre code, in which taste is identified by the pattern of afferent activity evoked in different fibres.

51
Q

This apparent discrepancy can be resolved by noting that afferent fibres receive broadly- tuned input, not only from the receptor cells via ATP released through gap junction hemichannels, but also from the presynaptic cells via serotonin release, which themselves receive purinergic input. Each afferent fibre can therefore respond to a range of taste qualities.

A

true

52
Q

fat

A

mamba

difficult

53
Q
A

MVST1B NHB (25 decks)

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