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Behavioral Neuroscience > Exam 2: Chemical senses (Smell and Taste) > Flashcards

Exam 2: Chemical senses (Smell and Taste) Flashcards

Taste and smell!!

1
Q

How is olfaction thought to work?

A
  1. Odorant molecules have characteristic shapes.

2. Dissolves in mucus and binds to olfactory receptor neurons in olfactory epithelium.

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2
Q

Smells project through what?

A

The cribiform plate of ethmoid bone (has many axons in the area that help detect smell)

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3
Q

Describe olfactory receptors.

A
  1. Short lived and constantly replaced
  2. Cilia project from dendrite to sample environment
  3. Axons project through cribiform plate to olfactory bulb
  4. Odorant binding proteins in mucus help concentrate or eliminate odorants
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4
Q

How many olfactory receptor genes are there in humans?

A

Approximately 400 genes in humans (other 600 have suffered mutations and no longer are expressed).

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5
Q

What type of receptors are olfactory receptors?

A

G-proteins using secondary messengers

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6
Q

How many genes does each olfactory receptor neuron express?

A

One gene each

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7
Q

How many olfactory receptors does a single odorant bind to?

A

Probably binds to several olfactory receptors with various affinity. The binding pattern is interpreted by brain as smell.

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8
Q

As odorant concentration increases, _________________.

A

Broader range of receptors stimulated

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9
Q

All neurons expressing particular receptor are found __________.

A

Scattered within one zone.

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10
Q

Different zones project to ____________.

A

Different parts of olfactory bulb (location of smells not known to be mapped accordingly).

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11
Q

Explain how receptors are differently sensitive.

A

Experiment with 3 smells and 3 receptors (A,B,C). EG. Isoamyl acetate (banana smell): A didn’t respond, B responded a little, and C responded greatly.

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12
Q

What are the steps for olfactory transduction?

A
  1. Odorant binds to G-protein coupled receptor
  2. Binding increases adenylyl cyclase activity
  3. cAMP opens cation channel
  4. Action potential generated
  5. IP3, cGMP, and CO also implicated in olfactory signaling.
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13
Q

How does adaptations to odorants work?

A
  1. Following exposure to odorants, they are no longer perceived. (When exposed to something for a long time, you become less responsive to the smell)
  2. Two mechanisms: Desensitization of receptor and Changes in sensitivity of cyclic nucleotide gated ion channel (less activated).
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14
Q

Where is the glomeruli and its function?

A

In olfactory bulb

  1. Receive afferent information from receptors
  2. Each odorant stimulates multiple glomeruli
  3. Each receives input from one type of receptor
  4. Spatial arrangement of glomeruli of different sensitivities consistent across animals
  5. Mitral and tufted cells project to olfactory cortex
  6. Periglomerular interneurons modify signals
  7. Top-down signals modulate bulb activity
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15
Q

What is olfactory pathway?

A

Glomeruli -> Lateral Olfactory Tract -> Cortex

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16
Q

What does the Olfactory cortex consist of?

A
  1. Anterior Olfactory Nucleus
  2. Piriform Cortex
  3. Amygdala
  4. Olfactory Tubercle
  5. Entorhinal Cortex
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17
Q

What is the overall function of the Olfactory Cortex?

A

Relays to orbitofrontal cortex via thalamus and is a direct connection to frontal lobe.

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18
Q

What does the amygdala project to?

A

Hypothalamus

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19
Q

What does the entorhinal cortex project to?

A

Hippocampus

20
Q

What does the thalamus project to?

A

Orbitofrontal cortex pathway important for conscious perception and discrimination

21
Q

What does the amygdala, hippocampus, and hypothalamus mediate?

A

Emotional and memory aspects

22
Q

What are the two theories of odor?

A
  1. Shape of odorant = smell

2. Molecular vibrations

23
Q

What is the gist of molecular vibration theory?

A

There are different molecules that give off the same smell even though its not the same shape. The frequency of vibrations from the molecules give off the smell.

24
Q

Human Olfactory abilities vary by what?

A

Age, sex, health status, internal hormones, specific anosmia

25
Q

Does odor have a correlation with memory?

A

Yes, strong odors were much more likely to evoke a vivid recollection than weak ones.

26
Q

What are pheromones?

A
  1. Chemical messages emitted to influence other members of same species.
  2. Influences reproductive and social behaviors (EG. Ants release pheromones to describe where food is)
27
Q

How are pheromones detected?

A

By olfactory system and vomeronasal system

28
Q

Do humans have vomeronasal systems? Animals?

A

No, it is where most animals stick their pheromone receptors.

29
Q

What is the vomeronasal system pathway?

A

Vomeronasal organ -> vomeronasal nerve -> accessory olfactory bulb

  1. Projects to amygdala, hypothalamus
  2. Not consciously perceived (never goes through thalamus)
  3. Influences reproductive physiology
30
Q

What are the five basic tastes?

A
  1. Sweet
  2. Bitter
  3. Umami (amino acid)
  4. Salty
  5. Sour
31
Q

How do we get “taste?”

A

Gustation combined with olfaction and somatosensory information = taste.

32
Q

Describe taste buds: how many receptors, where its found, how many types, what taste pores do.

A
  1. Each contains 50-100 taste receptor cells
  2. Taste pore allows tastants access to receptors
  3. Found on tongue, esophagus, palate
  4. Three forms found on different parts of tongue
33
Q

Taste buds are innervated by which CNs?

A

VII, IX, X

34
Q

What are the 3 forms of taste buds?

A
  1. Circumvallate (back of tongue)
  2. Foliate (back lateral sides of tongue)
  3. Fungiform (a lot towards tip of tongue)
35
Q

Taste receptors for bitter, sweet, and umami are what type of signaling?

A

GPCRs

36
Q

How do gene knockouts apply to sweet taste?

A

Affects perception of sweetness (uses adenyly clycase for cAMP)

37
Q

Describe how bitter taste is received.

A
  1. Large gene family (>30 receptors) coexpressed in individual receptor cells.
  2. Respond to wide variety of bitter compounds, but do not distinguish between them.
  3. (PLC -> DAG and IP3)
38
Q

What are two examples of umami taste?

A

Gluatamate and Aspartate

39
Q

Taste receptors for salty and sour use what type of signaling?

A

Ion channels

40
Q

Salty taste uses what type of channels?

A

Na+ channel (other salt cations probably use different receptors)

41
Q

Sour taste uses what type of channels?

A

Non-selective Ca2+, Na+, and H+ channels

42
Q

What are the two opposing views of how taste qualities are encoded in the periphery?

A
  1. Labeled-line model

2. Across-fibre model

43
Q

Describe the labeled line model for encoding of taste qualities in the periphery.

A
  1. Receptor cells are tuned to respond to single taste modalities - sweet, bitter, sour, salty, or umami - and are innervated by individually tuned nerve fibers.
  2. Each taste quality is specified by the activity of non-overlapping cells and fibres
    (supported by recent studies: activation of a single type of TRC is sufficient to encode taste quality)
44
Q

Describe the across-fibre pattern model for encoding taste qualities.

A
  1. Either individual TRCs are tuned to multiple taste qualities (indicated by various tones of grey and multicolored stippled nuclei) and consequently the same afferent fibre carries information for more than one taste modality
  2. TRCs are still tuned to single taste qualities but the same afferent fibre carries information for more than one taste modality
45
Q

What is the gustatory pathway?

A
  1. Neurotransmitter (possibly ATP) released from taste receptor cells to sensory fiber.
  2. Converted to action potentials and travel over cranial nerves VII, IX, X, XII to solitary tract nucleus in medulla.
  3. Project to thalamus
  4. Project to ipsilateral insula and operculum

Behavioral Neuroscience (9 decks)

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