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Neuro Exam 3 > Physiology of Olfaction and Gustation > Flashcards

Physiology of Olfaction and Gustation Flashcards

1
Q

What type of papillae does CN 7 innervate?

A

Fungiform

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2
Q

What type of papillae does CN 9 innervate?

A

Foliate

Circumvallate

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3
Q

Tastants are related to their chemical structures. Describe this for each of the taste categories.

A

Umami = glutamate

Salt = salt (ENaC)

Bitter = poisons, coffee

Sour = citrus, vinegar

Sweet = sugar, honey

Acid = sour

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4
Q

How is taste triggered?

A

Receptors depolarize with ligand binding

Causes opening of voltage gated Ca channels and triggers transmitter release

Neurotransmitter and mechanism of its release will differ by cell type

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5
Q

What neurotransmitter is release with sour and salt taste? What does it stimulate?

A

Serotonin

Stimulates post-synaptic primary gustatory neurons

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6
Q

What neurotransmitter is release with sweet, umami, and bitter taste? What does it stimulate?

A

ATP

Stimulates:
post-synaptic primary gustatory neurons

Pre-synaptic salty/sour receptor cells to stimulate serotonin release

Autocrine signaling

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7
Q

When activated, taste cells can activate themselves or neighboring cells. Name some ways of how this happens.

A

Sweet/umami/bitter cell will release ATP from Panx1 to trigger itself through P2Y/P2X.

It can trigger neighboring sour cell through P2Y.

Sour cell can inhibit neighboring sweet/umami/bitter with serotonin release

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8
Q

What is the mechanism by which salty is transduced in taste cells?

A

Salt enters through epithelial Na channel (ENaC)

Increases Na in saliva and on tongue

Na diffuses down gradient into cell

Depolarizers membrane

Increases intracellular Ca

Serotonin is released

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9
Q

What is the mechanism by which sour is transduced in taste cells?

A

Evoked by H+ ions

Inhibits K+ channels from flooding additional positive charge into cell

Depolarization

Increases intracellular Ca —> seratonin release

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10
Q

What is the mechanism by which sweet, umami, bitter is transduced in taste cells?

A

GPCR activates PLC-IP3 pathway —> increase intracellular Ca

TRPM5 activation —> Na intracellularly —> depolarization

Release of ATP through Panx1 channels

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11
Q

What is the GPCR receptor you need to know for umami?

A

mGluR4

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12
Q

Bitter has a high affinity for GPCRs. Why?

A

Poisons are bitter. So evolutionarily, to protect you from harm, bitter taste has a high affinity so that you don’t consume a lot of poison.

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13
Q

Describe the ascending taste pathway.

A

Secondary sensory neuron cell bodies = nucleus tractus solitarius

Ascends to synapse on tertiary sensory neuron cell bodies = VPM of thalamus

These ascend through posterior limb on IC and terminate in postcentral gyrus, frontal operculum, and insular cortex

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14
Q

Where can additional taste interpretation take place?

A

Orbitofrontal cortex

Integrates taste, olfaction, and visual cues regarding food
Appreciation of flavor, food reward, control of feeding

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15
Q

Where are additional taste responsive cells located? What do they do?

A

Amygdala - emotional and memories of taste

Hypothalamus - integration of homeostatic mechanism of hunger

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16
Q

What consists of the gustatory cortex? Where does it send input?

A

Postcentral gyrus
Frontal operculum
Insula

Sends input to amygdala

17
Q

What is significant about VPM of thalamus in regards to taste?

A

Discrimination of taste

18
Q

Where does the medullary reflex arc occur? What is it responsible for?

A

Occurs in the nucleus tractus solitarius

Responsible for salivating, swallowing, etc.

19
Q

How do Golf receptors work?

A

Stimulate adenylyl cyclase —> increases cAMP —> opens cyclic nucleotide gated channels (CNGC) —> cation influx —> depolarization of membrane

20
Q

What is adaptation? How is it occurring?

A

Adaptation = getting used to a smell and not noticing it

Occurs when odor persists:

1) sensitivity of CNGC to cAMP decreases —> reduces cation influx
2) inactivated by receptor phosphorylation = desensitization

21
Q

What is a glomerulus?

A

Collection of ORN projections from similar odorant receptors.

22
Q

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

A

One odorant can stimulate more than 1 type of OR

Combination of different OR stimuli act like “signature” of odorant

23
Q

Why does concentration of odorant matter?

A

At low concentrations, in dole smells floral, but a lot of it smells putrid

24
Q

Where does the anterior olfactory nucleus project?

A

Relay station to ipsi- and contralateral cortices

Also b/l olfactory bulbs and contralateral anterior olfactory nucleus

25
Q

What happens with the projection of piriform cortex —> lateral hypothalamus?

A

Control of appetite

Olfactory input influences appetite and hunger

26
Q

What happens with the projection of piriform cortex —> thalamus —> medial orbitofrontal cortex?

A

Integration of taste, sight, and smell

Appreciation of flavor of food

27
Q

What is the anterior cortical amygdaloid nucleus responsible for?

A

Emotional learning; olfactory fear conditioning

28
Q

What is the Periamygdaloid nucleus responsible for?

A

Integration of emotional aspect elicited by odor

29
Q

What happens with the projection of entorhinal cortex —> hippocampus?

A

Important in memory formation

Olfactory input facilitates both memory formation and recall

30
Q

What is the big difference in taste vs. olfactory receptors?

A

Taste receptors are modified epithelial cells, and olfactory receptors are neurons

31
Q

How are taste and olfactory receptors similar?

A

Has Na+ channels

Na gradient b/w ICF and ECF

32
Q

How do taste cells differ from olfactory cells?

A

Fixed permeability, shifting Na+ gradient

Relative INSENSITIVITY to voltage

Stay open at rest - fixed permeability

Flood ECF with Na+ gradient becomes steeper and Na flows into cell

Inward Na current depolarizes membrane to new voltage

33
Q

How do Olfactory cells differ from taste cells?

A

Fixed Na+ gradient, shifting permeability

Voltage SENSITIVITY

Maintains consistent Na gradient

Transient increase in Na conductance (permeability)

Voltage shifts, membrane depolarizes

34
Q

What is required for perception of flavor?

A

Gustatory input from gustatory cortex

Olfactory input from olfactory cortex - especially piriform cortex

Somatosensory information from mouth

MEDIAL ORBITAL CORTEX

35
Q

Adult neurogenesis is thought to occur in 2 places in brain. Where?

A

Olfactory bulb

Dentate gyrus of hippocampus

36
Q

Why does olfaction strongly affect memory?

A

Connections in temporal lobe overlays those of hippocampus and amygdala - important in setting mood and emotional behavior

Highly evocative experience of memory upon odor sensation

Neuro Exam 3 (8 decks)

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