4 - Physiology of Taste & Olfaction Flashcards
This is the term for the loss of sense of smell.
Anosmia
This is the term for the loss of sense of taste.
Aguesia
These are the chemical compounds that bind taste receptors and impart the primary flavor categories (sweet, salty, bitter, sour, umami).
Tastants
These are the chemical compounds that bind odorant receptors that impart an odor.
Odorants
What is the stimulus for sour tastant?
H+ ions
What is the neurotransmitter for sour tastant?
Serotonin
What is the stimulus for salty tastant?
Na+ binding ENaC
What is the neurotransmitter for salty tastant?
Serotonin
What is the stimulus for sweet tastant?
Sugars binding GPCRs
What is the neurotransmitter for sweet tastant?
ATP
What is the stimulus for umami tastant?
Glutamate binding mGluR4 (GPCR)
What is the neurotransmitter for umami tastant?
ATP
What is the stimulus for bitter tastant?
Various compounds – binding GPCRs
What is the neurotransmitter for bitter tastant?
ATP
Taste bud cells are specialized _________ cells. They have a distinct apical and basal domain.
Epithelial
Chemosensory transduction is initiated in the (BASAL/APICAL) domain and electrical signals are generated at the (BASAL/APICAL) domain via graded receptor potentials and release of neurotransmitters.
Apical
Basal
Taste receptor proteins and related signaling molecules are concentrated on the ________ that emerge from the apical surface. There are voltage-regulated ion channels as well as channels controlled by second messengers, particularly those of the transient receptor potential (TRP) receptor family.
Microvilli
For taste buds, intracellular ________ release facilitates synaptic vesicle fusion and extrusion of contained neurotransmitter to be released in to the basal synapse with local afferents. The activation of the afferent primary sensory neuron generates a receptor potential that if large enough may induce an _______ _______.
Calcium
Action Potential
Unlike taste cells, which are specialized epithelial cells, olfactory cells are bipolar neurons that release ________ as their primary neurotransmitter.
Glutamate
Odorants in the mucus directly bind to one of the receptor molecules located in the membranes of the cilia. This association activates an odorant-specific G-protein called ________, that in turn activates adenylate cyclase, resulting in the generation of second messenger ________.
Golf
cAMP
In olfactory cells, cAMP causes cation-sensitive channels to open and there is an influx of _______ and ______ resulting in depolarization. This then causes an opening of Calcium-gated ________ channels that provide the remainder of the depolarization needed to generate appropriate receptor potential.
Sodium
Calcium
Chloride
***Remember, sodium and calcium are influx and chloride is an efflux because it’s negative!
In olfactory cells, the receptor potential is reduced in magnitude when cAMP concentration drops due to enzymatic breakdown. In addition, recovery depends on the binding of calcium to _________ which reduces the affinity for the channel to cAMP.
Calmodulin
A robust response occurs when pleasant or purgent odors are presented. The odorant receptor itself can become __________, which modifies its sensitivity to odorants. These adaptations play a role in the perceived changes in awareness of smells as one “gets used to” a smell and no longer notices its strength.
Phosphorylated
Golf stimulates ________ ________ which increases cAMP. This opens cyclic nucleotide gated channels (CNGC), leading to cation influx and depolarization of the membrane.
Adenylyl Cyclase
As odorant stimulation persists, what two things can happen?
1) Sensitivity of the CNGC to cAMP decreases, reducing cation influx
OR
2) Inactivated by receptor phosphorylation (desensitization), meaning you “get used to” a smell and do not notice it anymore (adaptation)
Why can you not taste your food when you have a cold?
Thickened mucus blocks odorants from binding the odorant receptors. This is an example of reversible hyposmia.
***HYPERosmia has been identified in migraine, psychotic states, and pregnancy
Taste is the sensory modality that guides organisms to identify and consume nutrients while avoiding toxins and indigestible materials. This means recognizing the different tastes, which are…
Sweet Umami Sour Bitter Salty
This type of taste signals the presence of carbohydrates that serve as an energy source.
Sweet
This type of taste governs the intake of Na+ and other salts, essential for maintaining the body’s water balance and blood circulation.
Salty
This type of taste is generally believed to reflect a food’s protein content due to the presence of glutamate and a few other amino acids.
Umami
This type of taste signals the presence if dietary acids. Because it is generally aversive, we avoid ingesting excess acids and overloading the mechanisms that maintain acid-base balance for the body. Moreover, spoiled foods are often acidic and are thus avoided.
Sour
This type of taste is innately aversive and is though to guard against consuming poisons, many of which have this type of taste to humans.
Bitter
Because bitter taste is important in recognizing poisons or other harmful things, bitter-tuned GPCRs bind their ligand with very (LOW/HIGH) affinity compared to the other taste receptors. This has evolved as a means to detect potentially poisonous compounds, many of which bind a bitter-receptor, and taste it at very low concentration so to avoid additional ingestion of a potentially toxic substance.
High
T/F. People will still learn to tolerate and even seek out certain bitter- and sour-tasting compounds such as caffeine, green leafy vegetables, and citric acid (sour fruits), to essentially overcome innate taste responses.
True
Gustatory (and olfactory) sensitivity declines with _______. An obvious index of this decline is the tendency of adults to add more salt and spices to food than children do. The decreased sensitivity to salt can be problematic for older individuals with _________ as well as electrolyte and/or fluid problems. No safe alternative for table salt has been developed.
Age
Hypertension
As with aging, sensitivity to gustatory (and olfactory) cues are higher in _________. The sense of smell and taste begins in utero, where behaviorally it is believed to prime the growing fetus to the taste of ________ ________, which reflects the composition of the maternal diet and thus the external environment to which it would eventually be exposed and the subsequent localization of rooting for _________ after birth.
Childhood
Amniotic fluid
Breastmilk
Newborns respond to dilute _______ tastes. When this solution is placed in the oral cavity, the infant’s face relaxes and neural imaging shows that even 2-3 day old infants respond to it with a pattern similar to __________ stimulation.
Sweet
Pleasurable
Best investigated is the ability of ________ tastes to act as analgesics in infants and children during minor, painful procedures (but not during intensely painful or prolonged procedures).
Sweet
Small amounts of a sweet solution placed on the tongue of a crying newborn exert a rapid, calming effect along with decreased _______ ______ that persists for several minutes. This effect is exerted by sweetness in the oral cavity because direct stomach loading does not result in the same outcome.
Heart rate
Because of the effects sugar has on infants, ________ has been used to reduce procedural pain in infants with single painful events such as heel lance, venipuncture, and circumcision in the short-term.
Sucrose
Pain neurobiologists believe the analgesic effect of sweet-solutions arise from multiple mechanisms. Sucrose administration in postnatal rats has been shown to activate descending pain modulation centers such as the ________ ________ and ________ ________. However, since these descending pain control systems are generally immature in young infants, other mechanisms are likely involved.
Periaqueductal Gray
Raphe Nucleus
When given sweet tastes, general _______ _______ may be suppressed, leading to the infant being distracted from the procedure.
Brain arousal
The most widely accepted mechanism for sweet taste distracting infants is a sweet-tasted induced __________ release. This activates the endogenous opioid system.
Beta-Endorphin
The causes of age-related decline in preference for sweetness is unknown. Since it is best believed to be linked to the child’s need for ________ during catabolism for growth, this nutrient-source would invariably be less important upon reaching adulthood.
Calories
With the advent of _________ ________ added to many foods, it has become physiologically unreliable to biologically link levels of sweetness with caloric value or energy-content. The long-term effects of this biological unpredictability among children or adults are unknown.
Non-nutritive sweeteners
***i.e., Splenda
Because the active pharmaceutical ingredients in drugs by their very nature often taste unpleasant, with (SOUR/BITTER) taste a primary culprit, a central challenge of administering medicine to children is the “yucky taste”. In fact, usually the (MORE/LESS) potent a medication’s pharmacologic activity, the more (SOUR/BITTER) it tastes.
Bitter
More
Bitter
Although aversion to bitter is inborn, its flavor can be masked or blocked. _______ _______ suppress bitter taste at the level of the bitter-receptor.
Sodium salts
________ suppress the sense of bitterness at the cognitive level, which is why beverages containing _________ and _________ commonly contain this to mask the unwanted bitterness.
Sugars
Caffeine
Alcohol
***Sweeteners mask the caffeine and ethanol in the beverages
This receives multiple sensory inputs from the Vagus N. that relays information about the viscera. It is an early site of gustatory and visceral information. The reflex circuits form the basis for salivary secretions, mimetic responses, and swallowing.
Nucleus of the Solitary Tract
This is the relay state for taste perception in the thalamus. The discriminative aspects of taste are processed here.
Ventral Posterior Medial Nucleus (VPM)
What are the three areas that collectively make up the Gustatory Cortex?
Insular Taste Cortex
Operculum of Frontal Lobe
Post-central Gyrus
This is responsible for affective aspects of eating, emotional context to eating, and memories of eating.
Amygdala
This is responsible for the integration of homeostatic mechanisms of eating, like hunger.
Hypothalamus
Interplay between eating and the calming effects of food take place in the…
Limbic and reward system
This is responsible for integrating visual, somatosensory, olfaction, and gustatory stimuli to collectively appreciate the flavor of food (note: taste and flavor are NOT interchangeable terms).
Orbitofrontal Cortex
What does the perception of flavor require, and where do these all come together?
Gustatory input from Gustatory Cortex
Olfactory input from Olfactory Cortex
Somatosensory information from the mouth
These all come together in the Medial Orbitofrontal Cortex
Olfactory neurons synapse onto ________ and release glutamate. This then activates ______ and ______ cells that will project to the Olfactory Tract.
Glomeruli
Mitral
Tuft
What are the types of local interneurons within olfactory mucosa that release GABA and increase the specificity of the signal?
Periglomerular cells – Within glomeruli
Granular cells – In granule cell layer
In the olfactory system, this is the relay station to ipsilateral and contralateral cortices and is poorly understood.
Anterior Olfactory Nucleus
These have control of appetite and how olfactory input influences appetite and hunger.
Piriform Cortex
Lateral Hypothalamus
This is responsible for emotional learning, olfactory fear conditioning.
Anterior cortical amygdaloid nuclei
This is responsible for the integration of the emotional aspect of food as elicited by odor.
Periamygdaloid cortex
These are responsible for memory formation and how olfactory input facilitates both memory and recall. Connections within the limbic system and this are responsible for the highly evocative experience of memory upon odor sensation.
Entorhinal Cortex
Hippocampus
There exists an abundance of evidence that olfactory impairment is a common finding in neurodegenerative disease. In _________ disease, neurons of the olfactory system are among the first to demonstrate pathology, even sometimes years before a motor deficit is manifested.
Parkinson’s
T/F. Gustatory testing as a biomarker for early diagnostic strategies and prediction of clinical outcomes due to neurodegenerative diseases are becoming more widely used.
False. Olfactory testing as a biomarker for early diagnostic strategies and prediction of clinical outcomes due to neurodegenerative diseases are becoming more widely used.
What are the steps for taste evoked secretion of ATP?
Sweet, bitter, or umami tastant —
GPCR —
Activates signaling cascade —
Increases intracellular calcium —
TRPM5 activation (receptor that allows sodium influx) —
Depolarization —
Release of ATP through specific channels
What are the steps for salty tastant evoked secretion of serotonin?
Salty tastant —
Epithelial Na+ channel (ENaC) —
Increases the Na+ in saliva and on the tongue —
Na+ diffuses down gradient into the cell —
Depolarizes membrane —
Increased intracellular calcium —
Serotonin (5HT) release
What are the steps for sour tastant evoked secretion of serotonin?
Sour tastant —
H+ ions —
Depolarization —
Increased intracellular calcium —
Serotonin (5HT) release
The amygdala deals with emotional learning, but the ________ ________ deals specifically with the odor-induced emotional responses.
Periamygdaloid Cortex
