Gustation

Question 1

What are the 5 tastants and their general purpose for life?

Answer 1

sweet (nutritious)

sour (H+ for electrolyte maintenance)

salty (Na+ for electorlyte maintenance)

bitter (warning for toxins)

umami (nutritious)

Question 2

True or false: different regions of the tongue respond to different tastants.

Answer 2

FALSE

taste cells continaing receptors for all 5 tastants are found all over the surface of the tongue and oral cavity

Question 3

How often are taste receptors replaced?

Answer 3

every 10 days

Question 4

What are the transduction steps for sweet, bitter and umami taste?

Answer 4

1. receptor activation
2. Gustducin (G protein) activation
3. Second messenger system activation
4. channels open
5. depolarization
6. opening of VG Ca2+ channels or release of intracellular Ca2+ from stores
7. NT release onto primary afferent - ATP in this case

Question 5

What are the transduction steps for sour and salty tastes?

Answer 5

1. receptor activation
2. H+ or Na+ pass thorugh channel
3. Depolarization
4. Opening of VG Ca2+ channels or release of intracellular Ca2+
5. NT release on primary afferent - 5HT in this case

Question 6

Just to be clear…

what tastes use ATP as the NT? Which ones use serotonin?

Answer 6

ATP : sweet, bitter, umami

5HT: sour, salty

Question 7

What is the definition of the following?

Anosmia

hyposmia

hyperosmia

dysosmia

parosmia

cacosmia

Answer 7

Anosmia - complete absence of smell

hyposmia - reduced smell

hyperosmia - increased perception of smell

dysosmia - distorion of smell

parosmia - perception of smell when there is nothing there

cacosmia - extremely unpleasant perception of smell

Question 8

What is the defintion fo the following?

ageusia

hypogeusia

dysgeusia

cacgeusia

Answer 8

ageusia - complete absense of taste

hypogeusia - reduced perception of taste

dysgeusia - distortion of taste

cacgeusia - extremely unpleasant percepion of taste

Question 9

Flavor is a combination of what perceptions?

Answer 9

smell, taste, and texture

there’s lots of overlap beween gustatory and olfactory disorders

Question 10

What do patients with anosmia typically complain of?

Answer 10

ageusia as well - they usually think they’ve lost their sense of taste instead of smell

Question 11

In general, what is the issue with a peripheral loss of olfaction or gustation?

Answer 11

the chemical can’t reach the receptor or are altered on the way to the receptor

Question 12

What are some causes of peripheral loss of olfaction? gustation?

Answer 12

olfaction: smoking and anything that causes swelling of the nasal mucosa like rhinitis
gustation: smoking, dry mouth, hyperviscosity of saliva (as in CF)

Question 13

In general, what is the issue with a neuroepithelial loss of olfaction or gustation?

Answer 13

damage or absence of the receptor cells (or damage to their transduction mechanism)

Question 14

What are some causes of neuropeithelial loss of olfaction? gustation?

Answer 14

olfaction - congenital deficits, metabolic deficiencies, head injury (severing of the axons as they pass through the criribform plate, many drugs, aging

gustation: radiation, manyd rugs, aging

Question 15

What are the hallmarks of central issues causing olfaction or gustation loss?

Answer 15

hallucinations and loss of discrimination

Question 16

What are some examples of central issues causing olfaction or gustation deficits?

Answer 16

tumors

epilepsy

psychiatric disorders like depression adn schizophrenia

Question 17

Which are more common, gustatory or olfactory hallucinations?

Answer 17

olfactory are more common

Question 18

What is chemesthesis?

Answer 18

It’s the sensation you get when you eat a mint (coolness), a red hot candy (heat) or drink a carbonated beverage (irritation)

It’s not a taste, but rather activation of nerve endings that are partof the trigeminal nerve detectin pain and temperature

Question 19

Taste transmission from the tongue is carried to the brainstem by what two nervees?

Answer 19

facial (via chorda tympani) in anterior 2/3

glossopharyngeal on the posterior 1/3

Question 20

What provides “taste” sensation to the throat region?

Answer 20

the vagus nerve, but we don’t perceive information from these taste buds as sweet, salty, bitter, etc. It’s more ind etecting irritants that will cause us to cough or gag

Question 21

How is the chorda tympani carried to the tongue?

Answer 21

with the lingual nerve, which is a branch of V3

Question 22

Primary afferents innervating the taste buds will travel in the brainstem through what tract? To what nucleus?

Answer 22

through the solitary tract to the nucleus of the solitary tract

Question 23

Where in the brainstem is the solitary nucleus located?

Answer 23

in the medulla,

Question 24

Where in the solitary tract nucleus does taste information project? How is it mapped?

Answer 24

to the rostral end of the NST

mapped orotopically such that information from the tip of the tongue is most rostral and back of the throat is most caudal

Question 25

What is special about the “excitability” of the second order neurons in the NST?

Answer 25

their excitatbility depends on the hunger state of the animal

if its hungry - cells are very responsive

if not hungry - cells are less responsive

Question 26

Where do the second order neuron fibers project to from the NST? through what tract?

Bilaterally? Ipsilaterally? Contralaterally?

Answer 26

Through the taste lemniscus up to the ventral posterior thalamus (VPM)

bilaterally

Question 27

Remember that the VPM is somatotopic. WHere is taste represented?

Answer 27

it’s the most medial region

Question 28

What part of the cortex do the third order neurons project to?

Answer 28

the insular cortex - it’s where we consciously become aware of taste

Question 29

Projections from the insular cortex to what region integrates taste information with olfactory information to produce “flavor”.

Answer 29

orbitofrontal

Question 30

Not all of the information from the NST goes to the VPM though. What are some of the other regions?

Answer 30

1. hypothalamus/amygdala for visceral response and homeostasis
2. reticular formaiton for swallowing/coughing/gagging pattern generators

Question 31

What nucleus does the NST project to to initiate salivation?

Answer 31

the salivatory nucleus

Question 32

What nucleus does the NST project to to start moving the tongue during cheing and swallowing?

Answer 32

the hypoglossal nucleus

Question 33

What nucleus can initiate swallowing thoruhg motor output to the larynx and pharynx via CN9 and 10?

Answer 33

the nucleus ambiguus

Question 34

Ironically, what else is the nucleus ambiguus also involved in?

Answer 34

gagging and food rejection

Question 35

How can the nucleus ambiggus be important for both swallowing and gagging?

Answer 35

the reticular formation coordinates the pattern generators and swallowing and gagging really use the same muscles - they use have a different order of events

Question 36

For the gag reflex, what nerve carries the afferent information? the Efferent?

Answer 36

the glossopharyngeal nerve carries the afferent to the ipsilateral side

mostly bilateral activation of the vagus nerve via the nucleus ambiggus

Question 37

THrugh what nervee does the NST also monitor the internal chemical changes of the body?

through what portiont of the NST?

Answer 37

vagus

the more caudal part of the nucleus and tract

Question 38

Through what nucleus does the NST participate in visceral reflexes like heart rate and digestion?

Answer 38

the dorsal motor nucleus of the vagus nerve

(or via output to the sympathetic pathways)