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Neuroscience - Quizzes 1 - 3 > 2: Olfaction and Taste > Flashcards

2: Olfaction and Taste Flashcards

1
Q

Compare and contrast the chemical sensory functions of the trigeminal sensory system, the olfactory system, and the gustatory system.

A

Trigeminal system: protective function by detecting noxious and irritating stimuli

Olfactory system:

  • –High SENSITIVITY (down to a few molecules per sniff)
  • –Broad DISCRIMINATION (> a trillion molecules/combinations)
  • –Role in hunger/feeding, social interaction, reproduction, memories

Gustatory system: detects “flavor” as combination of sensory information
—Sweet, sour, bitter, salt, umami

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2
Q

Describe the role of the trigeminal sensory system and TRP receptors as a chemical sense in protection.

A

Nerve endings in mouth, face, mucous membranes

TRP channels: activated by changes in temperature and compounds that TASTE cool and hot/spicy
–Includes capsaicin TRP receptor

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3
Q

Describe the molecular mechanisms involved in development of odorant specificity.

A

Odorants depolarize olfactory receptor cells and cause a change in the rate at which they generate action potentials
—Each receptor is activated to a different extent by a large number of molecules

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4
Q

Discuss the mechanisms involved in changing sensitivity in the olfactory system in response to fear and hunger.

A

Emotional state (fear/excitement) -> enhanced sensitivity via EPI fibers

Locus ceruleus (Motivational state/hunger) -> enhanced sensitivity via norEPI fibers

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5
Q

Identify the locations of taste buds and different types of papillae. (4)

A

Non-uniform distribution of papillae on the tongue

  1. Vallate papillae (CN IX): largest, contain half of taste buds; like storage tanks, taste buds on side
    - –> On BACK of tongue
  2. Foliate papillae (CN IX, VII): leaf-like/ridge-like papillae on SIDES of tongue, taste buds on side
  3. Filoform papillae: NO TASTE BUDS
  4. Fungiform papillae (CN VII): taste buds on top
    - –> On anterior 2/3 of tongue
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6
Q

List mechanisms that are capable of altering taste sensitivity. (2)

A

Hunger -> 5HT, CCK -> enhance taste receptor cell sensitivity

Aldosterone, ADH -> regulate water balance by enhancing taste receptor cell sensitivity to SALT

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7
Q

What is an anosmia?

A

Selective olfactory deficits (can’t smell something specific)

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8
Q

Why could the age-related decline in olfaction be important?

A

Could be important in age-related malnutrition and lack of hunger

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9
Q

What problems arise when trying to study olfaction? (3)

A

Can’t predict smell based on structure
Combination of compounds may smell different from individual components
Molecule smell may depend on concentration

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10
Q

What is a vomeronasal organ? Is it present in humans?

A

Used to detect pheromones

Doubtful - genes not expressed; regresses during fetal development

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11
Q

List and describe the three types of cells in the olfactory epithelium.

A
  • -Basal cells: precursors for additional receptor cells (renew every 60 days)
  • -Receptor cells (neurons)
  • -Supporting cells: provide structural support
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12
Q

List and describe the three types of cells in the olfactory bulb.

A

Granule cells: interneurons
Mitral cells: the output cells of the olfactory bulb
Periglomerular cells: form synapses between neighboring glomeruli

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13
Q

What makes up a glomerulus?

A

Dendrites of a single mitral cell and axons of ~20,000 presynaptic neurons

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14
Q

How do cortical neurons function in odorant detection?

A

Cortical neurons compare information from multiple receptor types

  • –Compare amount of activity in multiple inputs
  • –Appear to have more of an ACROSS FIBER pattern for each odorant rather than a labeled line (when we respond to a single odorant, we look at the COMBINATION of glomeruli that are active
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15
Q

What is a “supertaster”?

A

Increased sensitivity to bitter substances (~25% of people)

Have a higher density of fungiform papillae on their tongue

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16
Q

What three cell types are in a taste bud?

A

Support cells
Basal cells: the precursors to taste cells (turn over every 10-12 days)
Taste receptor cells

17
Q

Outline the central projections of gustatory cells.

A

Release NT onto nerve endings (CN X, IX, VII), so they are NOT primary sensory neurons
Project to NUCLEUS OF SOLITARY TRACT
–Mediates salivation, coughing, gagging
-> VPM of thalamus
-> Gustatory cortex in insula (near somatosensory information from the tongue -> full sensation of taste)

NST also -> amygdala, hypothalamus

18
Q

Describe the coding of gustatory information in the cortex.

A

Individual taste receptor cells exhibit differential activation to tastants
–ACROSS-FIBER pattern, as in olfaction

19
Q

What effect does atrophic rhinitis have on chemical sensation?

A

Reduced olfactory abilities?

20
Q

What effect does diabetes have on chemical sensation?

A

Reduced olfactory abilities

21
Q

What effect does chronic renal failure have on chemical sensation?

A

Reduced olfactory and gustatory abilities

22
Q

What effect does Alzheimer’s disease have on chemical sensation?

A

Reduced olfactory abilities (loss of receptor cells)

23
Q

What effect does cystic fibrosis have on chemical sensation

A

Enhanced olfactory and gustatory abilities

24
Q

What effect does epilepsy have on chemical sensation?

A

Enhanced olfactory and gustatory abilities

25
Q

Describe the structure and function of olfactory receptor cells and their axons.

A

Sensory neurons in mucus layer in olfactory epithelium

CILIA play a key role in olfactory transduction: odorant on cilia -> depolarization; odorant on soma -> very little response

Unmyelinated axons travel through cribiform plate -> synapse on olfactory bulb

26
Q

Describe the molecular mechanisms involved in signaling in the olfactory receptor cell.

A

Primary mechanism: includes cAMP-gated and Ca-gated channels in the membranes of the cilia
–>Odorant molecule binds GPCR -> G(olf) protein -> AC -> cAMP -> **activate Na/Ca channel -> Na/Ca influx -> action potential

Secondary mechanism (for some odorants): involves IP3-gated ion channels (G-protein -> PLC -> IP3 -> activate Ca channel -> Ca influx -> action potential)

All olfactory receptors are GPCRs
—Have 950 olfactory receptor genes -> broad discriminatory powers

27
Q

Discuss convergence and glomerular specificity in terms of odorants.

A

CONVERGENCE: 25,000 neurons (all of the same odorant receptor type) project to the same glomerulus -> contributes to olfactory sensitivity

Different combinations of glomeruli activation -> different odorants

28
Q

Discuss the organization and termination of central processes of mitral cells.

A

Axons from mitral cells in olfactory bulb go to 3 places (NOT directly to the thalamus!

  1. PIRIFORM CORTEX (3-layered cortical region, primitive)
  2. Amygdala (emotions)
  3. Entorhinal cortex -> hippocampus (memory)

Then, -> thalamus, hypothalamus, orbitofrontal cortex

29
Q

Describe the differential specificities of different regions of the tongue.

A

Bitter is in the back (vallate papillae, CN IX)
Sour - along sides of the tongue (foliate papillae, CN IX/VII)
Salty - U-shape at tip of tongue (fungiform papillae, CN VII)
Sweet, umami - at tip of tongue (fungiform papillae, CN VII)

30
Q

Explain the mechanism involved in gustatory cells that sense sweet.

A

Saccharide compounds -> GPCR -> PLC -> IP3 -> Ca release from ER -> NT (ATP or 5-HT) released

31
Q

Explain the mechanism involved in gustatory cells that sense salty.

A

Amiloride-sensitive Na channel: constitutively open, allows Na and H to flow in -> depolarization -> Ca flows in -> NT (ATP or 5-HT) released

32
Q

Explain the mechanism involved in gustatory cells that sense sour.

A

H-activated channel -> allows Na and Ca to flow in -> depolarization -> more Ca flows in -> NT (ATP or 5-HT) released

33
Q

Explain the mechanism involved in gustatory cells that sense bitter.

A

Bitter compounds -> GPCR -> PLC -> IP3 -> Ca release from ER -> NT (ATP or 5-HT) released

34
Q

Explain the mechanism involved in gustatory cells that sense umami.

A

Glutamate -> GPCR -> PLC -> IP3 -> Ca release from ER -> NT (ATP or 5-HT) released

35
Q

Compare and contrast olfactory receptor cells and taste receptor cells. (4)

A

Both turn over frequently (gustatory turn over faster)
Olfactory receptor cells have axons, while gustatory cells do not
Single cells of each type respond to more than one molecule
Both -> coding via an across-fiber pattern of identification

Neuroscience - Quizzes 1 - 3 (30 decks)

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