4. Physiology taste & olfaction Flashcards
Anosmia
loss of sense of smell
Aguesia
loss of sense of taste
what are tastants
the chemical compounds that bind taste receptors and impart the primary flavor categories (sweet, salty, bitter, sour, unami)
what are odorants
the chemical compounds that bind odorant receptors that impart an odor
what are taste buds
& how do they work
specialized epithelial cells w/ apical & basal domain
Chemosensory transduction in apical domain & electrical signals generated at the basal domain via graded receptor potentials –> release NT.
- Taste receptor proteins and related signaling molecules are concentrated on the microvilli from apical surface. –> Vg ion channels & second messengers (TRP) .
- Intracellular Ca release –> synaptic vesicle fusion & release NT in basal synapse w/ local afferents
- activation of the afferents–> receptor potential if large enough –> AP
characteristics of sour tast
stimulated by H+ ions
NT = 5-HT
- presence of dietary acids. (aversive, avoid ingesting excess acids and overloading the mechanisms that maintain acid–base balance for the body) - spoiled food tastes sour
characteristic of salty
stimulated by Na binding ENaC
NT = 5-HT
intake of Na+ and other salts, essential for maintaining the body’s water balance and blood circulation.
characteristics of sweet taste
stimulus = sugars binding GPCRs
NT = ATP
foods signal the presence of carbohydrates that serve as an energy source
Umami taste characteristics
stimulated by Glu binding mGluR4
NT = ATP
- reflect a food’s protein content due to the presence of glutamate and a few other amino acids.
bitter taste characteristics
stimulated by various compounds binding GPCRs
NT = ATP
-innately aversive = guard against consuming poisons,(= bitter to humans) bitter-tuned GPCRs bind ligand with very high binding affinity ==> potentially poisonous compounds detected at very low concentration to avoid ingestion
how does sensory transduction of olfactory neurons occur
olfactory cells = bipolar - release Glu
- odorant bind receptor in membrane of cilia in mucosa
- activate Golf –> activate adenylyl cyclase –> increase cAMP
- cAMP opens cyclic nucleotide gated channels (CNGC) –> influx Na & Ca –> depol
- –> open Ca gated Cl channels –> remainder of depol
what occurs if odorant stimulation persists
- 1) sensitivity of the CNGC to cAMP decreases, reducing cation influx
- 2) is inactivated by receptor phosphorylation (desensitization)–> “get used to” (Adaptation)
why cant you taste food when you have a cold
Thickened mucus blocks odorants from binding the odorant receptors
–> example of r_eversible hyposmia._
what is hyperosmia
HYPERosmia has been identified in migraine, psychotic states, and pregnancy
heightened smell
what happens to taste & olfaction with age
declines with age
-add more salt to food –> can lead to HTN, electrolyte &/or fluid problems
when is gustation & olfaction sensitivity high
childhood
smell & taste begin in utero –> reflect maternal diet & rooting for breast milk after birth
what happens when you present sweet to newborn/infant
-face relaxes, imaging shows patterns of pleasure, calming effect w/ decreased HR
analgesic in infants & children for minor/painful procedures
how is sweet related to analgesic effects
postnatal rats –> activate descending pain modulation centers (PAG & raphe nuclei)
sweet taste induce beta-endorphin release, activating endogenous opiod system
how can bitter flavor be masked
sodium salts (monosodium glu & sodium gluconate) suppress lecel of bitter-receptor
sugar suppress bitterness at cognitive level
what is the role of nucleus of solitary tract
- receives multiple sensory inputs from CN X that relays information about the viscera.
- Early site of gustatory and visceral information.
- Reflex circuits forms basis for salivary secretions, mimetic responses and swallowing.
what is the role of VPM of thalamus
relay station for taste perception.
process discriminative aspects of taste
what makes up the gustatory cortex
Insular taste cortex, operculum of the frontal lobe, post-central gyrus
what is the role of hypothalamus & amygdala in taste
- Amygdala: Affective aspects of eating, emotional context & memories of eating
- Hypothalamus: Integrate homeostatic mechanisms of eating like hunger
- Interplay between eating and the calming effects of food take place in the limbic and reward system.
what is the role of orbitofrontal cortex in taste
Integrating visual, somatosensory, olfaction and gustatory stimuli to collectively appreciate the flavor of food
(note: taste and flavor are not interchangeable terms).
how does ant olfactory nucleus play into olfaction
- Relay station to ipsi- and contralateral cortices
what is the role of piriform cortex & lateral hypothalamus in olfaction
- control of appetite
- control how olfactory input influences appetite and hunger.
what is the role of piriform cortex & medial orbitofrontal cortex in olfaction
- integration of sight, smell, and taste of food.
- Appreciation of the flavor of food
how does ant cortical amygdaloid nuclei play into olfaction
emotional learning, olfactory fear conditioning
what is the role of periamygdaloid cortex
integrates the emotional aspect of food as elicitied by odor.
how does the entorhinal cortex & hippocampus play into olfaction
- memory formation
- how olfactory input facilitates both memory and recall.
- highly evocative experience of memory upon odor sensation
olfactory impairment could be signs of
neurodegenerative diseases
-seen in parkinson’s pts
