Phys. of Olfaction and Gustation Flashcards
Loss of sense of smell
Anosmia
Loss of sense of taste
Aguesia
Chemical compounds that bind to taste receptors and impart the primary flavor categories
Tastants
Chemical compounds that bind to odor receptors and impart odor
Odorants
List some things on the apical domain of the taste bud cells
Microvili, Tastant receptors, Voltage gated ion channels, TRP receptors
Salty and sour tastants enter taste bud cells via?
Voltage gated ion channels
Bitter, sweet and umami tastants activate taste bud cells via?
G-protein coupled receptors
Once tastants bind/enter the taste bud cells, then what happens?
The cell becomes depolarized with an influx of Na/Ca+ and then the cell releases its NTs which causes an AP to be sent to the brain
What is the taste bud cell released NT for sweet, bitter and umami tastants?
ATP
What is the taste bud cell released NT for salty and sour tastants?
Serotonin
ORN
Odorant Receptor Neurons
Olfactory cells are what type of neurons?
Bipolar
What NT do Olfactory cell neurons release?
Glutamate
What forms the olfactory mucosa?
Olfactory bipolar neurons AND Basal cells (supporting)
Since humans only have 350 odorant receptors, what can change the smell?
Stimulation of different receptors, combinations of receptors and concentrations of the odorant
Describe the process for depolarizing an ORN
- Odorant binds receptor and activates G protein (Golf)
- Golf activates Adenylate Cyclase to increase CAMP
- CAMP binds a Cyclic nucleotide Gated channel (CNGC) and allows Na/Ca to enter the cell
- Ca+ binds a Ca gated Cl- channel and allows chloride to leave the cell
- Further, more sodium enters using an exchanger
- Cell is more positive and thus depolarized and the AP can propagate down the ORN
ORN adaptation?
Getting used to a smell to where you no longer notice it
What are the 3 mechanisms for ORN adaptation?
- Enzymatic break down of cAMP = no cell depolarization
- Reduced affinity of the CNGC to cAMP reduces cation influx
- Odorant receptor becomes phosphorylated and less sensitive to odorants
What is bitter taste thought to guard against ingesting?
Toxins/poisons
Describe bitter-tuned GPCRs
They bind their ligand with very HIGH affinity compared to other taste receptors = can detect poisons at a very low concentration
Sweet tastants signal?
Presence of carbs - energy source
Salty tastants signal?
Intake of sodium essential for maintaining water balance in body
Umami tastants signal?
A food’s protein content due to amino acids
Sour tastants signal?
Presence of dietary acids
Usually over age 60, what happens to the gustatory system?
Decrease in taste bud number and remaining buds decrease in size - decreased sensitivity
Usually over age 70, what happens to the olfactory system?
Decreased nasal mucus production and receptors of ORNs decrease
What are some exogenous causes for decreased sensitivity in the gustation and olfactory systems?
Meds, diseases, smoking, pollutants
As a a result of age-related sensitivity decreases in the olfactory and gustation systems, what happens?
- Adults may add more salt and spice to their foods which can be a health concern for hypertension, etc.
- Loss of taste and smell can also result in malnutrition, impaired immunity and deterioration
Sensitivity to gustatory and olfactory cues are higher in ______ and start in ______
Childhood
Utero
Describe the effects of sweet tastes on newborns
Small amounts of sweet solution placed on tongue of crying newborn exerts a rapid, calming effect along with a decreased HR that can persist for a few minutes
What sweet solution is used in hospitals to give to newborns for minor procedures such as a blood draw?
Sucrose
Major mechanism behind the newborn-sweet solution effect?
Sweet taste induced beta-endorphin release, activating the endogenous opioid system (anti-nociceptive)
What is the cause for age-related decline in preference for sweetness?
Unknown
Many pharmaceutical ingredients taste unpleasant, what are 2 things that can suppress/mask their taste?
Sodium salts and/OR sugars
At what level do sodium salts mask the bitter taste?
At the bitter-receptor level
At what level do sugars suppress the bitter taste?
At the cognitive level
What makes up the physiologic gustatory cortex?
Postcentral gyrus, Frontal operculum, Insula
The perception of flavor requires what?
Gustatory cortex, olfactory cortex and somatosensory cortex
Where are all the inputs for perceiving flavor coming together and being integrated?
Orbitofrontal cortex
What CNs contribute taste?
CN VII, IX, X
Describe the pathway for gustation
- CN VII, IX, X go to the nucleus tractus solitarius
- From there the signal is relayed to the VPM of the thalamus
- Then on to the gustatory cortex
- The gustatory cortex sends signals to the orbitofrontal cortex and to the amygdala
- The amygdala and the hypothalamus interact with the nucleus tractus solitarius
Relay station for taste perception
VPM of thalamus
Discriminative aspects of taste
Gustatory cortex
Affective aspects, emotional aspects and memories of eating
Amygdala
Integrates homeostatic mechanisms of eating
Hypothalamus
Interplay between eating and calming effects
Limbic system
Basis for salivating, mimetic responses and swallowing
Medullary reflex arcs in the nucleus tractus solitarius
Olfactory neurons that express the same odorant receptors are then collected into?
1 glomerulus where ORNs synapse and release glutamate
Glomerulus ascends to what type of cell?
Mitral cells in the olfactory bulb
What does the olfactory tract NOT relay through?
Thalamus
4 main regions of the olfactory cortex?
Piriform cortex
Anterior cortical amygdaloid nucleus
Periamygdaloid cortex
Entorhinal cortex
What are the jobs of the piriform cortex?
Control of appetite and integration of taste, sight and smell
What is the job of the anterior cortical amygdaloid nucleus?
Emotional learning and olfactory fear conditioning
What is the job of the periamygdaloid cortex?
Emotional aspect elicited by odor
What is the job of the entorhinal cortex?
Important in memory formation and recall upon odor sensation
Where does the entorhinal cortex project?
Hippocampus
Loss of smell due to thickened mucus that blocks odorants from binding
Reversible Hyposmia
Increased sense of smell
Hyperosmia
Where has hyperosmia been seen?
With migraines, pregnant women and psychotic states
Where are the 2 areas in the brain where neurons will reform (neurogenesis)?
Olfactory bulb and the dentate gyrus of hippocampus
With what disease has olfactory neuron impairment (pathology) been seen?
Parkinson’s disease - often before motor deficits occur
Responsible for appreciating all aspects of food
Orbitofrontal cortex
