2/6: Taste and Smell Flashcards
What are the peripheral organs of gustation?
Taste papillae
What do papillae contain?
Taste buds
What is the functional unit of gustation?
Taste buds
Compare the number of taste buds of adults vs children
Adults have 3,000-10,000 taste buds, children have more
After 45 years, many taste buds degenerate
What kind of cells to taste buds contain?
Taste receptor cells
- epithelial cells, NOT neurons
- supporting cells (maintain environment)
- basal cells
Where are taste receptors located?
On cilia - very HIGH turnover rate
What are the locations of taste papillae?
Tongue, hard and soft palate, pharynx, epiglottis, larynx
What are the types of papillae?
Circumvallate, filiform, fungiform, foliate
Where are circumvallate papillae located?
Dorsal surface of tongue, make V-shaped line
Where are foliate papillae located?
Posterolateral border of tongue
Where are fungiform papillae located and what do they look like?
Anterior dorsal surface of tongue
Look like red spots
What taste bud is non-gustatory?
Filliform papillae
What is the function of filliform papillae?
Increase surface area to increase contact and friction for food
Where are extralingual papillae located?
On soft and hard palates, larynx, epiglottis, and pharynx
What kind of taste bud to supertasters have an increase of?
Fungiform papillae
All tastants must dissolve in ________
Saliva
Individual taste receptor cells are sensitive to ________________
A specific taste stimulus (sweet, bitter, etc)
Olfaction is vital for _________________
Normal gustation (so when sick, things don’t taste right)
What kind of families of taste receptor genes account for sweet, bitter, and umami?
TR1 and TR2
What g-protein do TR1 and TR2 utilize?
G protein - gustducin
Metabotrobic receptor
What kind of receptors are sour and salty detected by?
Ion channel linked receptors
What are sour tastes stimulated by?
H+, protective taste
If something is sour = more protons
What are the receptors for sour taste?
a. Amiloride-sensitive epithelial Na+ channel
(ENaC), H+ channels, blockade of K+ channels.
b. All potential mechanisms lead to depolarization
of receptor cells
What is sour taste strongly linked to?
Salivation and contraction of facial muscles
ex: miracle berries have miraculin which decreases pH and is an agonist of sweet receptors
What are stimuli for sweet taste?
Sugars
Glycols
Alcohols
Artificial sweeteners (saccharine, aspartame, sucralose)
What receptor family is sweet?
T1R
What to T1R2 and T1R3 proteins make?
A dimer that is G-protein linked
- broadly sensitive to sweet-tasting substances (glucose, sucrose, saccharin, etc)
What are stimuli for bitter taste?
K+
Denatonium
Caffeine
Strychnine
Quinine
Nicotine
Broccoli
Brussel sprouts
Bitter taste is considered what kind of a taste?
Protective; highest number of receptors and lowest threshold for perception (food that is spoiled, it is protecting us against)
What receptors are associated with bitter taste?
T2R family
What are denatonium salts?
Colorless and odorless solids that are used to prevent inappropriate ingestion (denatured alcohol, antifreeze, nail biting preventions, liquid soaps, etc.).
What are salty taste stimulated by?
Na+ and somewhat by Cl-
What receptors are salty?
ENaC (Na+ channel)
Cl0 via paracellular transport
What is the stimulus for Umami?
Monosodium glutamate (MSG), enhanced by ribonculeotides
What is the receptor for Umami?
Metabotropic glutamate receptor (g-protein coupled receptor)
What is taste threshold?
Minimum concentration at which a substance can be perceived
- The threshold concentrations of substances to which the taste buds respond vary with the particular substance
- Some toxic substances such as strychnine have a bitter taste at very low concentrations, preventing accidental ingestion of this chemical, which causes fatal
convulsions.
What are the steps of the taste signaling cascade in the mouth?
- The Ca2+ activates the TrpM5 channel to allow the entry of sodium ions, depolarizing the cell
- The combination of depolarization resulting from the influx of Na+ and rise in intracellular Ca2+ opens pannexin channels in the taste-cell membrane, releasing ATP from the cell
- Activates purinergic receptors on the sensory nerve fibers innervating the taste buds
- Signal is sent to the brain
Where do sweet or glutamate rich foods bind to?
T1R-class receptors
Where do bitter substances bind to?
T2R receptors which stimulate the release of Ca2+ into the cytosol from the endoplasmic riticulum via G protein signaling and the second messenger molecule IP3
Where are aforementioned taste receptors found?
In the stomach, bile duct, intestines, bronchi, kidneys
What are sweet and bitter receptors like in the gut?
– Sweet receptors may be involved in insulin stimulation
– Bitter receptors in stomach stimulate CCK (satiety) &
emesis
– Bitter receptors in colon induce osmotic gradient ->
diarrhea
When does taste specificity work best?
Low ligand concentrations
Taste does not solely depend on combinations of the aforementioned 5 receptors, but also on:
a. Smell (!!!!)
b. Fat, electric, metallic, pain, temperature
c. Taste modifiers
What are the 5 things that alter taste perception?
- Taste Specificity is best at low ligand concentrations
- Taste does not solely depend on combinations of the
aforementioned 5 receptors - Taste Aversion
- Taste Adaptation (threshold for sensitivity can change)
- Taste Preference. Genetic, cultural influences.
What are supertasters?
Have more taste buds and more afferent gustatory neurons
More responsive to other tastant types
How is taste transmitted into the CNS?
- Taste receptor cells synapse on first order neurons
- Second order neurons
- Third order neurons
Describe first order neurons that transmit taste to the CNS
a. redundant, bilateral innervation
b. neurons enter the CNS via caranial nerves VII, IX, or X
What does the facial nerve (CN VII) supply?
*Chorda Tympani Branch—anterior
2/3 of the tongue
*Greater petrosal superficial nerve—
papillae on soft palate
What does the glossopharyngeal (CN IX) nerve supply?
Posterior 1/3 of the tongue
What does the vagus nerve (CN X) supply?
Pharynx, epiglottis, larynx
Describe second order neurons that transmit taste to the CNS
Cell bodies in the gustatory division of the nucleus of the solitary tract (in the medulla (nucleus tractus solitariim=, NTS))
What is the nucleus tractus solitarii (NTS)?
Purely sensory nucleus in the medulla and it receives input for taste, chemoreceptors, aortic bodies
Describe third order neurons that transmit taste to the CNS
Cell bodies in the central posteromedial nucleus of the thalamus
Free endings of many trigeminal pain fibers are found in the _________
Olfactory epithelium
What are trigeminal fibers stimulated by?
Irritating substances, which lead to characteristic of “odor” of such substances as peppermint, menthol, and chlorine
Activation of these endings by nasal irritants also initiates sneezing, lacrimation, respiratory inhibition, and other reflexes
Where is the olfactory membrane located?
In superior and posterior portions of each nostril
What kind of neurons are olfactory membranes?
Primary afferent neurons
Receptor cells are bipolar neurons that have a short peripheral process that extends into the mucosa where it ends in an
expended olfactory knob. The knob gives rise to several cilia that form a
dense mat at the mucosal surface.
The cilia interact with odorants in mucus
What are cells of the olfactory membrane?
Sustentacular/supporting cells
Basal Cells
- New receptor cells generated every 60 days from basal cells and they
must form synapses with mitral cells in the olfactory bulb
Bowman’s glands
Where do axons of the olfactory receptor cells pass through and synapse?
pass through the
Cribriform Plate of the Ethmoid bone to synapse with Mitral Cells in the Olfactory Bulb
What are glomeruli?
globular structures in the
olfactory bulbs and it is
where the short axons
from olfactory receptor
cells terminate. Each
glomeruli is the terminus for ~25,000 axons and dendrites from mitral cells
Describe olfactory receptors and their action potentials
Generate continuous action potentials
Olfactory receptor cells with one type of odorant receptor project to?
One olfactory glomerulus (OG)
Olfactory receptor cells
with another type of
receptor project to>
A different OG
Where are olfactory receptor proteins located?
Cilia
What are g-protein coupled receptors (Golf) coupled to?
Adenylyl cyclase
What does inreased levels of cAMP do?
Open sodium channels to depolarize the olfactory neuron
- other receptors may act via other 2nd messengers
To be perceived, odorants must
a. Be volatile (spread in air—small)
b. Be partially water-soluble
c. Be partially lipid-soluble
d. Reach olfactory mucosa (normal breath vs. sniff)
50% of adaptation is achieved…
In the first second
- further receptor adaptation is limited and slow
Large numbers of centrifugal nerve fibers pass from the olfactory regions of the brain backward along the
olfactory tract and terminate on
Special inhibitory cells in the olfactory bulb, the granule cells
How is smell perception terminated?
Odorants must diffuse away, be broken down by enzymes, or adaptation occurs
What are the ways of coding of olfaction (knowing a certain smell)
a. Olfactory receptor proteins are NOT dedicated
to single odorants
b. Different olfactory receptor proteins respond
differently to the same odorants
c. Across-Fiber Pattern Code (not a labeled line (if it was a labelled line, then one would activate another)
Information conveyed by relative amount of
activity across multiple, differentially sensitive elements in an array.
Where does the olfactory tract enter the brain?
At the junction between the midbrain and the cerebrum and divides into to pathways
What two pathways does the olfactory tract divide into?
- Medial olfactory area/primitive olfactory system
- Lateral olfactory area
Where does the Medial olfactory area/primitive olfactory system travel to?
Hypothalamus and limbic system for olfactory reflexes
What are the two subcomponents of the lateral olfactory system?
- The less old olfactory system
- Newer system
What is the less old olfactory system?
Automatic but learned control of food intake and aversion to toxic and unhealthy foods
What is the less old olfactory system linked to?
Limbic system (hippocampus - memory)
What is the newer olfactory system?
Conscious perception and analysis of olfaction
What is the newer olfactory system linked to?
Orbitofrontale cortex (temporal lobe)
What are the distortions of gustation?
-guesia
* Normogeusia
* Hypogeusia
* Hypergeusia
* Parageusia
* Taste Agnosia
* Ageusia
What are dysgeusias classified as?
Qualitative or quantitative
What is dysgeusia due to?
Medications (ACE inhibitors, statins, chemotherapy
drugs, proton pump inhibitors), nutritional
deficiencies (zinc deficiency, vitamin A), etc
What are the distortions of olfaction?
-osmia
* Normosmia
* Hyposmia
* Hyperosmia
* Parosmia
* Olfactory Agnosia
* Anosmia
What are olfactory disorders frequently associated with?
Aging
- may be a better predictor for alzheimer’s disease and other dementias
Which disorders are not associated with aging?
Gustatory disorders
Complaints of gustatory disorders are complaints often due to?
Olfactory, salivary, or neurologic dysfunction
What can gustatory disorders be associated with?
Oral products and medications can alter
taste (& smell): anti-plaque mouthwash,
toothpaste, hydrocortisone, lidocaine,
tetracycline, captopril, penicillamine
What can olfactory disorders be associated with?
- Frequently associated with aging
May be better predictor of Alzheimer’s
Disease & other dementias than global
cognitive tests - Smoking & Upper Respiratory Tract
Infections - Head Trauma
- Neurodegenerative Diseases, Tumors
- Medications can Alter Smell
What does halitosis cause?
Alkaline saliva, decreased saliva, inflammation
What are a few systemic diseases that alter breath?
- TB, pneumonia, lung cancer, tonsillitis
- Hiatal hernias, gastroesophageal reflux, gastric
ulcer - Achalasia
- Diabetic Ketoacidosis
- Hepatic and renal failure
