Olfaction and Gustation

Question 1

5 taste categories and what they respond to

Answer 1

Bitter—poisons, coffee
Salty—salt
Sweet —sugar, honey
Sour—citrus, vinegar
Umami—glutamate

Question 2

Receptor potentials of taste cells are usually depolarizing, which involves opening of voltage-gated ____channels and NT release, which depends on cell type.

Sour and salty trigger release of NT ______, while sweet, bitter and umami trigger release of ______

Answer 2

Calcium

Serotonin; ATP

Question 3

3 destinations of ATP released from sweet, umami, and bitter receptor cells

Answer 3

1. Post-synaptic primary gustatory neurons
2. Pre-synaptic salty/sour receptor cells to stimulate serotonin release
3. Autocrine signaling

Question 4

Serotonin released from salt/sour receptor cells stimulates ______ neurons

Answer 4

Post-synaptic primary gustatory neurons

Question 5

Receptor potentials of taste cells are usually depolarizing, which involves opening of voltage-gated ____channels and NT release, which depends on cell type.

Sour and salty trigger release of NT ______, while sweet, bitter and umami trigger release of ______

Answer 5

Calcium

Serotonin; ATP

Question 6

3 destinations of ATP released from sweet, umami, and bitter receptor cells

Answer 6

1. Post-synaptic primary gustatory neurons
2. Pre-synaptic salty/sour receptor cells to stimulate serotonin release
3. Autocrine signaling

Question 7

Serotonin released from salt/sour receptor cells stimulates ______ neurons

Answer 7

Post-synaptic primary gustatory neurons

Question 8

Mechanisms by which 5 taste qualities are transduced in taste cells

Answer 8

Sweet, umami, bitter via GPCR

Salt via ENaC

Sour via proton-sensitive channel

Question 9

Sweet tastants activate GPCRs, activating PLC-IP3 pathway and increasing intracellular Ca, eventually activating _____ which is what results in depolarization and release of ATP through ____ channels and NT release

Answer 9

TRPM5; PanxI

Question 10

Umami has the same pathway as the sweet and bitter tastants, but activates a specific GPCR, the ____

Answer 10

mGluR4

Question 11

Which tastant binds with highest affinity?

Answer 11

Bitter - for poison detection

Question 12

Taste buds are innervated by special visceral afferent neurons including:

Anterior tongue: Chorda tympani branch of facial nerve with cell bodies in the geniculate ganglion and termination in the ____________

Posterior tongue: lingual branch of glossopharyngeal n. with cell bodies in petrosal ganglion and termination in the ________

Epiglottis: superior laryngeal branch of vagus n. with cell bodies id nodose ganglion and termination in _________

Answer 12

Nucleus tractus solitarius (gustatory area) x3

Question 13

In the ascending taste pathway, secondary sensory neurons cell bodies are in the nucleus tractus solitarius, which ascends to synapse on tertiary sensory neuron cell bodies in the _____ of the thalamus. These neurons ascend through the posterior limb of the internal capsule and terminate in the gustatory cortex which is made up of the _____, ____, and _____

Answer 13

VPM

Postcentral gyrus, frontal operculum, and insular cortex

Question 14

Additional taste interpretation takes place in the ____ cortex which integrates taste, olfaction, and visual cues regarding food (appreciation of flavor, food reward, and control of feeding)

Additional taste responsive cells are located in the ___ and ____ which are involved in emotional context and memories of taste

Answer 14

Orbitofrontal

Amygdala; hypothalamus

Question 15

In what part of the ascending taste pathway are there medullary reflex arcs for salivating, swallowing, etc?

Answer 15

Nucleus tractus solitarius

Question 16

Olfactory receptors are GPCRs, specifically _____ which stimulates AC, increasing cAMP, and opening ______ channels, leading to cation influx and membrane depolarization

Answer 16

G[olf]; cyclic nucleotide gated channels (CNGC)

Question 17

What happens to sensitivity of the CNGC to cAMP as odorant stimulation persists?

Answer 17

It decreases, reducing cation influx, or it is inactivated by receptor phosphorylation

Basically desensitizing you to the odor

Question 18

One oflactory neuron expresses the same odorant receptor on all of its cilia. Then the projections of similar odorant receptors are collected into one ____

Answer 18

Glomerulus

Question 19

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

Answer 19

One odorant can stimulate more than one type of OR

The combinations of different OR stimuli act like a “signature” of that odorant

[concentration of odorant also makes a difference, odorants smell different at different concentrations]

Question 20

Cell types of olfactory bulb

Answer 20

Mitral cells
Granule cells
Periglomerular cells

Question 21

Olfactory neurons synapse onto glomeruli and release ______

Periglomerular cells are local interneurons and release ______, increasing specificity of the signal

_____ cells and tufted cells will project to the olfactory tract

Granular cells are local interneurons and release ____, further increasing specificity of odorant signal

Answer 21

Glutamate

GABA

Mitral

GABA

Question 22

T/F: the olfactory system is the only sensory system that does not route through the thalamus before connecting to the cortex

Answer 22

True

Question 23

Components of olfactory cortex

Answer 23

Anterior olfactory nucleus
Olfactory tubercle
Piriform cortex
Anterior cortical amygdaloid nuclei
Periamygdaloid cortex
Lateral entorhinal cortex

Question 24

The _____ _______ nucleus is a relay station for olfactory info to ipsilateral and contralateral cortices and it is poorly understood

Answer 24

Anterior olfactory

Question 25

The piriform cortex projects to the ____ ____ and functions in control of appetite and hunger

Answer 25

Lateral hypothalamus

Question 26

The piriform cortex also projects to the ______, then the _______ to control integration of taste, sight, and smell — thus the appreciation of flavor of food

Answer 26

Thalamus; medial orbitofrontal

Question 27

Which olfactory cortex functions in emotional learning and olfactory fear conditioning?

Answer 27

Anterior cortical amygdaloid nucleus

Question 28

Which olfactory cortex functions in integration of emotional aspects elicited by odor?

Answer 28

Periamygdaloid cortex

Question 29

The entorhinal cortex projects olfactory info to the ____ which is important in memory formation

Answer 29

Hippocampus

Question 30

What is the difference in Na+ gradient and permeability in olfactory neurons vs. taste cells?

Answer 30

Olfactory neurons exhibit fixed Na+ gradient and shifting permeability

Taste cells exhibit fixed permeability and shifting Na+gradient

Question 31

Perception of flavor requires gustatory input and olfactory input as well as somatosensory info from the mouth, this information is organized by the ____ ___ cortex

Answer 31

Medial orbitofrontal cortex

Question 32

T/F: loss of taste is often an olfaction problem

Answer 32

True

Question 33

How/why does olfaction strongly influence memory?

Answer 33

The connections in the temporal lobe overlay those of the hipposcampus and amygdala, components of the limbic system, which is important in setting mood and emotional behavior

These are the areas responsible for associating emotional response with odors. Presumably these areas are also responsible for highly evocative experience of memory upon odor sensation