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NE Exam 3 > Physiology Of Olfaction And Gustation > Flashcards

Physiology Of Olfaction And Gustation Flashcards

1
Q

What is anosmia?

A

Loss of sense of smell

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2
Q

What is aguesia?

A

Loss of sense of taste

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3
Q

What are tastants?

A

The chemical compounds that bind taste receptors and impart the primary flavor categories (sweet, salty, bitter, sour and umami)

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4
Q

What are odorants?

A

The chemical compounds that bind odorant receptors that impart an odor

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5
Q

Describe the apical domain of a taste cell

A

Location of chemosensory transduction

Contain microvilli, tastant receptors, voltage gated ion channels and TRP receptors

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6
Q

The basolateral domain of a taste is the location of what?

A

NT release

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7
Q

What is the stimulus and NT for sour tastants?

A

Stimulated by H+ ions (acid) (use cation channel)

NT = serotonin

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8
Q

What is the stimulus and NT for salty tastants?

A

Stimulated by Na binding ENaC (epithelial Na channel)

NT = serotonin

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9
Q

What is the stimulus and NT for sweet tastants?

A

Stimulated by sugars binding GPCRs

NT = ATP

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10
Q

What is the stimulus and NT for umami tastants?

A

Stimulated by glutamate binding mGluR4 (GPCR)

NT = ATP

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11
Q

What is the stimulus and NT for bitter tastants?

A

Various compounds binding GPCRs

NT = ATP

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12
Q

What are the steps for the taste signaling pathway?

A

Ligand binds receptor on apical domain —> depolarizing receptor potential occurs within taste cell —> depolarization opens voltage gated Ca channels and triggers NT release —> NT binds to receptor on nearby primary sensory afferent neuron —> receptor potential is generated —> AP generated —> signal sent to brain

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13
Q

What are odorant receptor neurons (ORNs)?

A

Bipolar neurons that release glutamate as their NT and have axons coming off their central terminal going to the brain
Sensitive to odorants
ORNs + their supporting (basal) cells = olfactory mucosa

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14
Q

How do we detect 12 million odors with only 350 different odorant receptors?

A

One odorant can stimulate more than one type of odorant receptor
The combinations of different OR stimuli act like a signature of that odorant that we then learn to identify

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15
Q

Explain how concentration of an odorant matters

A

At different concentrations an odorant can produce different responses (smells)
Ex. At low concentrations indole smells floral but at high concentrations it smells putrid (rotting)

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16
Q

What are the steps for the sensory transduction pathway occurring in ORNs?

A
  1. Odorant diffuses into nasal mucous, binds to Golf (GPCR) on olfactory cilia and activates the olfactory cell
  2. Second messenger cAMP is activated
  3. CAMP binds to and opens a cyclic nucleotide gated channel (CNGC) allowing Na and Ca influx into the cell
  4. Depolarization occurs
  5. Ca gated Cl channels open and provides remainder of depolarization needed to generate appropriate receptor potential to achieve an AP in the ORN
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17
Q

What is adaption to smell?

A

Perceived changes in awareness of smells as one gets used to a smell and no longer notices its strength

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18
Q

What are the three mechanisms for smell adaptation?

A
  1. Receptor potential is reduced in magnitude due to enzymatic breakdown of cAMP which decreases its concentration
  2. Ca binding to calmodulin reduces the affinity for the GNGC channel to cAMP reducing cation influx
  3. Phosphorylation of the OR which modifies its sensitivity to odorants (inactivates it)
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19
Q

Describe bitter tastant receptors and the high affinity for their ligands

A

Bitter taste is innately aversive and guards against ingesting poison (which taste bitter)
As a result bitter-tuned GPCRs bind their ligand with very high binding affinity compared to other taste receptors
This has evolved so that we can detect poisons at low concentrations to avoid additional ingestion of it
However the innate taste receptors have been overcome by people seeking bitter foods like coffee

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20
Q

What is the significance of sweet, salty, umami and sour tastants?

A

Sweet foods signal presence of carbs = energy source
Salty taste governs Na intake = maintaining body’s water balance and blood circulation
Umami reflects a foods protein content due to presence of glutamate/other aa
Sour taste signals presence of acids = acid-base balance; also spoiled foods are sour

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21
Q

How does gustatory sensitivity change with age?

A

Number of taste buds decrease
Remaining taste buds shrink in size
Mouth produces less saliva -> dry mouth affects taste
Occurs especially after the age of 60

22
Q

How does olfactory sensitivity change with age?

A

Decreased nasal mucous production
Fibers and receptors of ORNs decrease with age
Especially after age 70

23
Q

What are some exogenous causes of gustatory and olfactory sensitivity decline?

A

Medications, diseases, smoking, exposures to toxins and pollutants in the air

24
Q

Why is a decreased sensitivity to salt problematic?

A

Adults tend to add more salts and spices to food than children do
Problematic for older individuals with HTN as well as electrolyte and/or fluid problems
Loss of taste and smell can result in appetite suppression, weight loss, malnutrition, impaired immunity, depression and deterioration in medical conditions

25
Q

Describe gustation and olfaction in the fetus

A

Sense of smell and taste begins in utero
Primes the growing fetus to the taste of amniotic fluid which reflects the composition of maternal diet
Maternal diet represents the fetus’s future external environment
Also primes rooting for breast milk after birth through smell and taste sensitivity

26
Q

Describe newborns response to sweet tastes

A

Sweet tastes in the oral cavity provide a rapid calming effect along with decreased HR
Can act as an analgesic during minor painful procedures
This effect is exerted by sweetness in the oral cavity bc direct stomach loading doesnt result in the same outcome

27
Q

What are the three mechanisms explaining the analgesic effect of sweet solutions?

A
  1. General brain arousal may be suppressed leading to the infant being distracted from the procedure
  2. Rewarding effect of sweet flavors blunts stress response promoting calmer affect
  3. Anti-nociceptive action (the most widely accepted mechanism is sweet taste induced beta endorphin release activating the endogenous opioid system)
28
Q

Describe masking the taste of pharmaceutical ingredients

A

Bitter taste of pharmaceutical ingredients in drugs causes the challenge of administering medicine to children
The more potent a medications pharmaceutical activity the more bitter it is
Bitter taste can be blocked even tho its innate
Na salts (monosodium glutamate and Na gluconate) suppress bitter taste at the level of the bitter receptor*
Sugars suppress the sense of bitterness at the cognitive level*

29
Q

What 3 cortical areas make up the gustatory cortex?

A

Postcentral gyrus, frontal operculum and the insula

30
Q

The perception of favor requires what?

A

Gustatory input from the gustatory cortex, olfactory input from the olfactory cortex, and somatosensory info from the mouth
These factors all come together in the medial orbitofrontal cortex

31
Q

What is the role of the nucleus tractus solitarius (NTS) in the processing of taste?

A

Early site of gustatory-visceral integration

32
Q

What is the role of the VPM of the thalamus during processing of taste?

A

Relay station for taste perception and begins discriminative aspects of taste

33
Q

What is the role of the gustatory cortex during processing of taste?

A

Discriminative aspects of taste

34
Q

What is the role of the orbitofrontal cortex during processing of taste?

A

Integrates visual, somatosensory, olfaction and gustatory stimuli

35
Q

What is the role of the amygdala during processing of taste?

A

Affective aspects of eating, emotional context to eating and memories of eating

36
Q

What is the role of the hypothalamus during processing of taste?

A

Integrates homeostatic mechanisms of eating (such as hunger)

37
Q

What is the role of the limbic system during processing of taste?

A

Interplay between eating and calming effects of food

38
Q

What is the role of medullary reflex arcs during processing of taste?

A

Form basis for salivating, mimetic responses and swallowing

39
Q

Describe the cellular connections in the olfactory mucosa and olfactory bulb

A

One olfactory neuron expresses the same odorant receptor on all of its cilia
Then the projections of similar odorant receptors are collected into one glomerulus (located in the bulb)
Olfactory neurons synapse onto glomeruli and release glutamate

40
Q

What cells are located in the olfactory bulb?

A

Mitral cells which project to the olfactory tract
Granule cells and periglomerular cells which are local interneurons that release GABA and increase specificity of the signal

41
Q

What is the only sensory system that does not route through the thalamus before connecting to the cortex?

A

Olfaction
Olfactory mucosa -> olfactory bulb -> olfactory cortex -> hypothalamus, DM thalamic nucleus, insular and orbital cortex, hippocampus

42
Q

What structures make up the olfactory cortex?

A

Anterior olfactory nucleus, olfactory tubercle, piriform cortex, anterior cortical amygdaloid nucleus, periamygdaloid cortex, lateral entorhinal cortex

43
Q

What is the function of the anterior olfactory nucleus?

A

Relay station to ipsilateral and contralateral cortices

44
Q

What is the function of the piriform cortex?

A

Projects to hypothalamus: controls appetite
Can also route to thalamus -> medial orbitofrontal cortex: integration of taste, sight and smell + appreciation of the flavor of food

45
Q

What is the function of the anterior cortical amygdaloid nucleus?

A

Emotional learning, olfactory fear conditioning

46
Q

What is the function of the periamygdaloid cortex?

A

Integration of emotional aspect elicited by odor

47
Q

What is the function of the entorhinal cortex?

A

Projects to hippocampus
Important in memory formation
Olfactory input facilitates both memory formation and recall
Connections with the limbic system and entorhinal cortex are responsible for the highly evocative experience of memory upon odor sensation

48
Q

What is an example of reversible hyposmia?

A

Thickened mucus during a cold which blocks odorants from binding to their receptors

49
Q

Hyperosmia has been observed with what conditions?

A

Migraines, psychotic state and pregnancy

50
Q

What are the two locations where adult neurogenesis can occur in the brain?

A

The olfactory bulb and the dentate gyrus of the hippocampus

NE Exam 3 (16 decks)

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