Gustation Flashcards
What are the 5 tastants and their general purpose for life?
sweet (nutritious)
sour (H+ for electrolyte maintenance)
salty (Na+ for electorlyte maintenance)
bitter (warning for toxins)
umami (nutritious)
True or false: different regions of the tongue respond to different tastants.
FALSE
taste cells continaing receptors for all 5 tastants are found all over the surface of the tongue and oral cavity
How often are taste receptors replaced?
every 10 days
What are the transduction steps for sweet, bitter and umami taste?
- receptor activation
- Gustducin (G protein) activation
- Second messenger system activation
- channels open
- depolarization
- opening of VG Ca2+ channels or release of intracellular Ca2+ from stores
- NT release onto primary afferent - ATP in this case
What are the transduction steps for sour and salty tastes?
- receptor activation
- H+ or Na+ pass thorugh channel
- Depolarization
- Opening of VG Ca2+ channels or release of intracellular Ca2+
- NT release on primary afferent - 5HT in this case
Just to be clear…
what tastes use ATP as the NT? Which ones use serotonin?
ATP : sweet, bitter, umami
5HT: sour, salty
What is the definition of the following?
Anosmia
hyposmia
hyperosmia
dysosmia
parosmia
cacosmia
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
What is the defintion fo the following?
ageusia
hypogeusia
dysgeusia
cacgeusia
ageusia - complete absense of taste
hypogeusia - reduced perception of taste
dysgeusia - distortion of taste
cacgeusia - extremely unpleasant percepion of taste
Flavor is a combination of what perceptions?
smell, taste, and texture
there’s lots of overlap beween gustatory and olfactory disorders
What do patients with anosmia typically complain of?
ageusia as well - they usually think they’ve lost their sense of taste instead of smell
In general, what is the issue with a peripheral loss of olfaction or gustation?
the chemical can’t reach the receptor or are altered on the way to the receptor
What are some causes of peripheral loss of olfaction? gustation?
olfaction: smoking and anything that causes swelling of the nasal mucosa like rhinitis
gustation: smoking, dry mouth, hyperviscosity of saliva (as in CF)
In general, what is the issue with a neuroepithelial loss of olfaction or gustation?
damage or absence of the receptor cells (or damage to their transduction mechanism)
What are some causes of neuropeithelial loss of olfaction? gustation?
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
What are the hallmarks of central issues causing olfaction or gustation loss?
hallucinations and loss of discrimination
What are some examples of central issues causing olfaction or gustation deficits?
tumors
epilepsy
psychiatric disorders like depression adn schizophrenia
Which are more common, gustatory or olfactory hallucinations?
olfactory are more common
What is chemesthesis?
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
Taste transmission from the tongue is carried to the brainstem by what two nervees?
facial (via chorda tympani) in anterior 2/3
glossopharyngeal on the posterior 1/3
What provides “taste” sensation to the throat region?
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
How is the chorda tympani carried to the tongue?
with the lingual nerve, which is a branch of V3
Primary afferents innervating the taste buds will travel in the brainstem through what tract? To what nucleus?
through the solitary tract to the nucleus of the solitary tract
Where in the brainstem is the solitary nucleus located?
in the medulla,
Where in the solitary tract nucleus does taste information project? How is it mapped?
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
What is special about the “excitability” of the second order neurons in the NST?
their excitatbility depends on the hunger state of the animal
if its hungry - cells are very responsive
if not hungry - cells are less responsive
Where do the second order neuron fibers project to from the NST? through what tract?
Bilaterally? Ipsilaterally? Contralaterally?
Through the taste lemniscus up to the ventral posterior thalamus (VPM)
bilaterally
Remember that the VPM is somatotopic. WHere is taste represented?
it’s the most medial region
What part of the cortex do the third order neurons project to?
the insular cortex - it’s where we consciously become aware of taste
Projections from the insular cortex to what region integrates taste information with olfactory information to produce “flavor”.
orbitofrontal
Not all of the information from the NST goes to the VPM though. What are some of the other regions?
- hypothalamus/amygdala for visceral response and homeostasis
- reticular formaiton for swallowing/coughing/gagging pattern generators
What nucleus does the NST project to to initiate salivation?
the salivatory nucleus
What nucleus does the NST project to to start moving the tongue during cheing and swallowing?
the hypoglossal nucleus
What nucleus can initiate swallowing thoruhg motor output to the larynx and pharynx via CN9 and 10?
the nucleus ambiguus
Ironically, what else is the nucleus ambiguus also involved in?
gagging and food rejection
How can the nucleus ambiggus be important for both swallowing and gagging?
the reticular formation coordinates the pattern generators and swallowing and gagging really use the same muscles - they use have a different order of events
For the gag reflex, what nerve carries the afferent information? the Efferent?
the glossopharyngeal nerve carries the afferent to the ipsilateral side
mostly bilateral activation of the vagus nerve via the nucleus ambiggus
THrugh what nervee does the NST also monitor the internal chemical changes of the body?
through what portiont of the NST?
vagus
the more caudal part of the nucleus and tract
Through what nucleus does the NST participate in visceral reflexes like heart rate and digestion?
the dorsal motor nucleus of the vagus nerve
(or via output to the sympathetic pathways)
