Taste and Smell Flashcards
— — are the peripheral organs of gustation
Taste Papillae
Papillae contain — —, the functional units of gustation
Taste Buds
Adults have — taste buds. Children
have —. After — years, many taste buds
degenerate.
3,000-10,000
more
45
Taste Buds contain
Taste Receptor Cells
Taste Receptor Cells are --- Cells, not neurons. Receptors are on ---. VERY high --- rate.
Epithelial
cilia
turnover
Taste Buds contain Taste Receptor Cells, including (3)
taste receptor cells
supporting cells
basal cells
Location of Taste Papillae (6)
Tongue, Hard & Soft Palate, Pharynx, Epiglottis, Larynx
1000s of tastes are differentiated primarily based on the
activation of – different receptors.
5
All tastants must dissolve in —
saliva
Individual taste receptor cells may be sensitive to
a specific taste stimulus, but many taste receptor
cells have receptors for
multiple taste types
— is vital for normal gustation.
Olfaction
(3) tastes are accounted for
by two families of taste receptor genes– TR1 &
TR2, both of which utilize the G protein gustducin.
Sweet, bitter, and umami
(2) are detected by ion channel linked
receptors.
Sour and salty
Sour Taste is stimulated by
H+, Protective taste (blocks K+ exit, increase in IC K+, depolarization)
Sour taste:
Multiple candidate receptors (2)
a. Amiloride-sensitive epithelial Na+ channel
(ENaC), H+ channels, blockade of K+ channels.
b. All potential mechanisms lead to depolarization
of receptor cells
Sour Taste:
strongly linked to (2)
salvation and contraction of facial muscles
Sweet taste:
Lots of stimuli: (7)
sugars, glycols, alcohols, artificial sweeteners (saccharine, aspartame, sucralose)
Sweet taste:
T1R receptor family is important.
Specifically, T1R2 & T1R3 proteins make
a dimer that is — linked
G-protein
T1R receptor family is important. Specifically, T1R2 & T1R3 proteins make a dimer that is G-protein linked i. Broadly sensitive to sweet-tasting substances. ii. Sweet receptors are usually NOT on the same cells as
bitter & umami.
Bitter Taste:
Stimuli are usually organic: (8)
K+, denatonium, caffeine, strychnine, quinine, nicotine, broccoli, brussel sprouts
Bitter taste:
Protective taste:
highest number of
receptors and lowest threshold for
perception
Bitter taste: Multiple Receptors (50-80) in --- family
T2R (G PROTIEN)
Denatonium salts are colorless
and odorless solids that are
used to prevent
inappropriate
ingestion (denatured alcohol,
antifreeze, nail biting
preventions, liquid soaps, etc.).
Salty:
Stimulated mostly by – and somewhat by –
Na+
Cl-
Salty:
Receptor: (2)
i. ENaC (Na+ channel)
ii. Cl- via paracellular transport?
Umami:
Stimulus:
monosodium glutamate, enhanced by
ribonucleotides
Umami:
Receptor:
i. Metabotropic glutamate receptor (mGLuR4 receptor)
Taste threshold refers to
the 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
— substances tend to have the lowest
threshold
Bitter
Some toxic substances such as
strychnine have a bitter taste at very low
concentrations, preventing
accidental
ingestion of this chemical, which causes fatal
convulsions
substance: HCl
taste:
threshold:
taste: sour
threshold: 100 umol/L
substance: NaCl
taste:
threshold:
taste: salt
threshold: 2000 umol/L
substance: Strychine HCl
taste:
threshold:
taste: bitter
threshold: 1.6 umol/L
substance: glucose
taste:
threshold:
taste: sweet
threshold: 80,000 umol/L
substance: sucrose
taste:
threshold:
taste: sweet
threshold: 10,000 umol/L
substance: Saccharin
taste:
threshold:
taste: sweet
threshold: 23 umol/L
taste receptors are also found in the (5)
stomach, bile duct, intestines, bronchi, & kidneys
Despite the similarities in receptor molecules and signaling
cascades, however, only the chemoreceptive systems in the mouth
evoke a sensation of taste. The others, researchers are learning,
serve different functions depending on their —
location
Perhaps protective in the airways—stimulating
sneezing,
respiratory escalator
In the gut (3)
– Sweet receptors may be involved in..
– Bitter receptors in stomach stimulate…
– Bitter receptors in colon induce…
insulin stimulation
CCK (satiety) & emesis
osmotic gradient which leads to diarrhea
Taste Specificity is best at — ligand concentrations
low
Taste does not solely depend on combinations of the aforementioned 5 receptors, also (3)
a. Smell
b. Fat, electric, metallic, pain, temperature
c. Taste modifiers
Taste Adaptation (2)
a. Only about 50% occurs at the receptor
b. Threshold for sensitivity can change
Taste Preference (2)
Genetic, cultural influences.
Taste Perception (5)
- Taste Specificity is best at low ligand concentrations
- Taste does not solely depend on combinations of the aforementioned 5 receptors
- Taste Aversion
- Taste Adaptation
- Taste Preference
Are you a Non-Taster,
Medium Taster,
or Supertaster?
• Differences once thought to be solely dependent on
genes for bitter taste receptor
Supertasters (2)
have more taste buds and more afferent gustatory neurons.
Are also more responsive to other tastant types.
Nontasters tend to have higher
body weights
– There may also be a link to fat perception
Taste Receptor cells synapse on
first order neurons
Taste Receptor cells synapse
on first order neurons (2)
a. Redundant, bilateral
innervation
b. Neurons enter the CNS via
Cranial Nerves VII, IX, or X
Facial Nerve (CN VII) (2)
•Chorda Tympani Branch—anterior
2/3 of the tongue
•Greater petrosal superficial nerve—
papillae on soft palate
Glossopharyngeal (CN IX) -
posterior 1/3
of the tongue
Vagus Nerve (CN X) - (3)
pharynx, epiglottis,
larynx
Second Order Neurons Cell
bodies in the
gustatory division of the nucleus of the solitary tract (in the medulla (nucleus tractus solitarii, NTS)
The NTS is a purely sensory
nucleus in the medulla and it
receives input for (3)
taste,
chemoreceptors, aortic
bodies, etc.
Third Order Neurons Cell
bodies in the
ventral
posteromedial nucleus of
the thalamus
Humans are able to differentiate
10000 odors with a relatively
poorly developed olfactory
epithelium of only
10-40 million
receptor cells
Free endings of many trigeminal pain fibers are found in the olfactory epithelium.
They are stimulated by
irritating substances
Free endings of many trigeminal pain fibers are found in the olfactory epithelium.
They are stimulated by irritating substances, which leads to the characteristic “odor” of such substances as (3)
peppermint, menthol, and chlorine
Activation of these endings by nasal irritants also initiates (4)
sneezing, lacrimation, respiratory inhibition, and other reflexes
Anatomy of Olfactory Membrane (5)
- In superior & posterior portions of each nostril
- Olfactory Cells are primary
afferent neurons - Sustentacular/Supporting Cells
- Basal Cells
- Bowman’s Glands
Receptor cells are --- neurons that have a short peripheral process that extends into the mucosa where it ends in an expended olfactory knob
bipolar
The knob gives rise to several — that form a
dense mat at the mucosal surface.
The cilia interact with — in
mucus.
cilia
odorants
New receptor cells generated every – days from basal cells and they
must form synapses with
60
mitral cells in the olfactory bulb
Axons of the Olfactory Receptor Cells pass through the
Cribriform Plate of the Ethmoid bone to synapse with
Mitral
Cells in the Olfactory Bulb.
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.
RMP of olfactory receptor cell is — mV so the receptor cells will generate continuous APs (1 every 20 seconds to 2-3 per second).
-55
Odorants cause depolarization to — mV, which causes an increase in AP frequency (20-30 per second)
-30
The rate of AP signals varies in proportion to logarithm of
stimulus
strength
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
There are > — functional olfactory
genes in humans and multiple types of
olfactory receptors
500
G-protein coupled receptors (Golf),
coupled to
adenylyl cyclase
Increased levels of cAMP open sodium channels to
depolarize the
olfactory neuron
Other receptors may act via other
2nd
messengers
To be perceived, odorants must (4)
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
Adaptation
a. –% of adaptation is achieved in the first
second
b. Further receptor adaptation is (2)
50
limited and slow
A postulated neuronal mechanism for adaptation. “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
it has been postulated that after the onset of an olfactory stimulus,
the CNS quickly develops
strong feedback inhibition to suppress relay of the smell signals through the olfactory bulb
Termination of Smell Perception: (3)
Odorants must diffuse
away, be broken down by enzymes, or adaptation occurs
Coding of Olfaction (3)
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)
Information conveyed by relative amount of
activity across multiple, differentially
sensitive elements in an array.
CN I -
Olfactory Nerve/Tract
The olfactory tract enters the
brain at the junction between
the (2) and divides into two pathways.
midbrain and the cerebrum
The olfactory tract enters the
brain at the junction between
the midbrain and the cerebrum
and divides into two pathways (2)
Medial Olfactory Area/ Primitive Olfactory System
Lateral Olfactory Area
Medial Olfactory Area/ Primitive Olfactory System
to hypothalamus
and limbic system for
olfactory reflexes
Lateral Olfactory Area (2)
i. The Less Old Olfactory System: to limbic system (hippocampus) ii. Newer System: to orbitofrontale cortex
The Less Old
Olfactory System
Automatic but learned control of food
intake and aversion to toxic and unhealthy
foods
Newer System
Conscious perception and analysis of
olfaction.
information is transmitted from the olfactory bulb by axons
of
mitral and tufted relay neurons in the lateral olfactory
tract
Gustation (6)
- Normogeusia
- Hypogeusia
- Hypergeusia
- Parageusia
- Taste Agnosia
- Ageusia
Olfaction (6)
- Normosmia
- Hyposmia
- Hyperosmia
- Parosmia
- Olfactory Agnosia
- Anosmia
Gustatory Disorders
1. Generally not associated with
aging
Gustatory Disorders
Complaints often due to (3)
olfactory, salivary,
or neurologic dysfunction
Gustatory Disorders
Oral products and medications can alter
taste (& smell)
Olfactory Disorders
1. Frequently associated with
aging
May be better predictor of Alzheimer’s
Disease & other dementias than global
cognitive tests
