Physiology of Gustation and Olfaction Flashcards
What stimulus and subsequent NT release allows for the taste sensation of: sour
- Stimulus is through H+ ions (acid)
- NT = Serotonin
What stimulus and subsequent NT release allows for the taste sensation of: Salty
- Stimulus: Na+ binding epithelial Na+ channel (ENaC)
- NT: Serotonin
What stimulus and subsequent NT release allows for the taste sensation of: Sweet
- Stimulus: sugars binding GPCR
- NT: ATP
What stimulus and subsequent NT release allows for the taste sensation of: Umami
- Stimulus: mGluR4 (GPCR)
- NT: ATP
What stimulus and subsequent NT release allows for the taste sensation of: Bitter
- Stimulus: various compounds binding GPCR
- NT: ATP
Sensory Transduction in odorant receptor neurons (ORN)
- Odorants diffuse into nasal mucus, binds olfactory receptor proteins (G_olf) on olfactory cilia and activates olfactory cell
- Activated G_olf activates adenylate cyclase to convert ATP –> cAMP (second messenger)
- cAMP binds and opens cyclic-nucleotide gated channels (CNGC) to allow Na+ and Ca2+ to influx into cell
- Increased [Ca2+] causes Ca2+-gated Cl- channels to open and resultant Cl- outflow to depolarize the cell
Mechanisms of olfactory receptor neuron (ORN) adaptation to smell
- Receptor potential reduced in magnitude as cAMP is enzymatically broken down
- Ca2+ binding calmodulin reduces cyclic-nucleotide gated channels affinity for cAMP
- Odorant receptor itself can become phosphorylated to decrease its sensitivity to the odorant
Physiological significance of: Bitter foods
- Innately aversive to guard against poisons –> GPCRs have a higher binding affinity to this ligand than the other tastes
- Detects poisons at low [] to avoid additional ingestion
Physiological significance of: Sweet foods
-Signal presence of carbohydrates (energy source)
Physiological significance of: Salty foods
-Governs Na+ and other salt intake to maintain body’s water balance and blood circulation
Physiological significance of: Umami
-Reflects a food’s protein content based on presence of AA (especially glutamate)
Physiological significance of: Sour
- Generally aversive b/c avoid ingesting excess acids which can overload acid-base balance + spoiled foods are often acidic
- Signals presence of dietary acids
Age-related decrease in gustatory sensitivity
- Especially after 60 yo
- Mouth produces less saliva
- # taste buds decreases and remaining taste buds shrink in size
Age-related decrease in olfactory sensitivity
- Especially after 70 yo
- Decreased nasal mucus production
- Fibers and receptors of odorant receptor neurons decrease w/ age
Mechanisms causing analgesic effect of sweet-solutions
- Anti-nociceptive action - most widely accepted mechanism is sweet-tasted induced beta-endorphin release which activates endogenous opioid system
- General brain arousal may be suppressed –> distraction
- Rewarding effect of sweet flavors blunts stress-response –> calmer affect
What are some chemically-induced ways to suppress bitter taste?
- Sodium salts (e.g. monosodium glutamate and sodium gluconate) suppress @ lvl of the bitter-receptor
- Sugars suppress @ cognitive lvl b/c this receptor is more prominent in brain
Name the inputs required for the perception of flavor
- Gustatory input from gustatory cortex
- Olfactory input from olfactory cortex
- Somatosensory information from mouth
* All these factors come together in the medial orbitofrontal cortex
Function in processing taste: Nucleus tractus solitarius
- Early site of gustatory-visceral integration
- Receives inputs from CN VII, IX and X, as well as, from amygdala and hypothalamus
- Projects to the ventral posteromedial nucleus of the thalamus
Function in processing taste: ventral posteromedial nucleus (VPM) of thalamus
- Relay station for taste perception
- Begins discriminative aspects of taste
- Receives input from nucleus tractus solitarius and projects to the gustatory cortex (post-central gyrus, frontal operculum and insula)
Function in processing taste: gustatory cortex (Post-central gyrus, frontal operculum and insula)
- Discriminative aspects of taste
- Receives information from ventral posteromedial nucleus of the thalamus and projects to the amygdala and the orbitofrontal cortex
Function in processing taste: orbitofrontal cortex
- Integrates visual (what food looks like), somatosensory (texture of food), olfaction (smell of food) and gustatory (taste of food) stimuli
- Receives input from the gustatory cortex (post-central gyrus, frontal operculum and insula)
Function in processing taste: amygdala
- Affective aspects of eating, emotional context to eating and memories of eating
- Receives information from the gustatory cortex and projects back to the nucleus tractus solitariius
Function in processing taste: hypothalamus
- Integrates homeostatic mechanisms of eating (e.g. hunger)
- Projects to the nucleus tractus solitarius
Function in processing taste: Limbic system
-Interplay b/w eating and calming effects of food involves limbic and reward systems
