Physiology of Olfaction and Gustation (Pierce) Flashcards
Sour
stimulus:
NTM:
H ions
Serotonin
Salty
Stimulus:
NTM:
Na binding ENaC
Serotonin
Sweet
Stimulus:
NTM:
Sugars binding to GPCR
ATP
Umami
Stimulus:
NTM:
glutamate binding to mGluR4
ATP
Bitter
Stimulus:
NTM:
various compounds binding to GPCRs
ATP
Olfactory Physiology
How we smell
How we “get used to” a smell
Golf stimulates adenylyl cyclase which increases cAMP which opens cyclic nucelotide gated channels leading to cation influx and depol. of the membrane
As odorant stimulation persists sensitivity of the CNGC to cAMP decreases, reducing cation influx OR is inactivated by receptor phosphorylation (desenstization) meaning you “get used” to a smell and do not notice it (adaptation)
Olfactory cells are bipolar and use what NTM?
What ions/channels contribute to depolarization?
glutamate
binding of the odor to the Golf which activates AC and cAMP allows cation sensitive channels to open in response to Na and Ca influx, leading to depol. and opening of Ca gated Cl channels to provide the remainder of the depolarization needed to generate a receptor potential
enzymatic breakdown of cAMP, calcium-calmodulin binding, and receptor phosphorylation all contribute to what?
scent adaptation (“getting used to” a smell)
What is the significance of bitter tastants high binding affinity with their receptor?
Many poisons are bitter tasting thus, bitter-tuned GPCRs bind their ligand with very high affinity as a means to detect potentially posonois compounds.
It is sensitive even in low concentrations to bitter compounds
same goes with sour foods (sour things have a lot of acid, and generally spoiled foods may have increased acid content)
Describe age-related changes in gustatory sensitivity
taste and smell decrease with age
as such, older people tend to add more salt/spices to food which can contribute to HTN, fluid/electrolyte imbalances, etc.
Why do children and infants prefer sweet foods?
- sweet foods tend to indicate higher calorie foods (although this is evolving with the invention of zero calorie sweetners)
- sweet tastes induce beta endorphin release, activaing enogenous opiod system in infants
Why are many liquid medications sweet tasting?
the more potent a drug is, typically the more bitter it tastes (same goes with caffiene and alcohol)
MSG and sodium gluconate can block bitter at the receptor level
sugar can supress the sense of bitterness at a cognitive level
What is the role of the Solitary Tract Nucleus in taste?
receives multiple sensory inputs from the vagus nerve that relays information about the viscera
early site of gustatory and visceral info
reflex circuits forms basis for salivary secretions, mimetic responses for swallowing
What is the role of the ventral posterior medial nucleus of the thalamus in terms of taste?
relay station for taste perception
discriminative aspects of taste are processed here
What makes up the gustatory cortex?
insular taste cortex, operculum, post-central gyrus
