phys of olfactory sys Flashcards
what is anosmia?
lack of sense smell
what is aguesa?
lack of sense of taste
what are tastants?
chemical compounds that bind taste receptors and impact primaty flavor
what are odorants?
chemical compounds that bind odorant receptors
what are tastebuds?
specialized epithelial cells
apical and basal domains
how is chemosensory tranduction done in taste buds
started in apical domain, electrical signals generated in basal domain via graded recepors
release NT
where are taste receptor proteins concentrated?
concentrated in microvilli that emerge from apical surface
explain how receptor potentials are produced in taste bud cells?
what can it cause
voltage regulated ion channels, secondary messenger channels, esp TRP
intracellular calcium release facilitates synaptic vesicle fusion
NT released onto basal synapse with local afferents
causes receptor potential
if large enoguh, can cause action potential
what are olfactory cells, and what do they release?
bipolar neurons that release glutamate as primary NT
where do odorants bind and what do they activate? name the steps
receptor molecules in cilia
activate specific G protein
activate adenylate cyclase
activates cAMP
cation sensitive channel opens and influxes Na and Ca
depolarization, opening of Ca and Cl- cannels
more depolarization, generate receptor potential
what reduces receptor potential magnitude for olfaction?
drop in cAMP due to enzymatic breakdown
Calcium binds to calmodulin, reducing affinity for channel to cAMP
odorant receptor can be phosphorylated
what happens if odorant receptor gets phosphorylated
modifies sensitifvity to odors
get used to smell
how foes the olfactory cascade work?
Golf stimulates adenylyl cyclase
increasing cAMP
opens cyclic nuleotide gated channels
cation influx
depolarization of membrane
what happens when odorant stimulation persists?
sensitivity of CNGC to cAMP decreases, cation influx reduced
or
inactivated by receptor phosphorylation
(get used to it)
what cant you taste your food if you have a cold?
thickened mucus blocks odorants from binding to odorant receptors
“hyperosmia”
sweet foods signal what?
presence of carbs
salty foods signal what
intake of Na, which maintains bodys water balance and blood circulation
umami signals what?
reflect foods protein content due to glutamate
sour signals what?
dietary acids
avoid ingesting this food, might be bad
bitter taste signals what?
innately bad mkay
guards against consuming poisons
bitter GPCRs bind ligand very tightly, taste bitter at low concentrations
but you can overcome taste responses
what happens to olfaction as you age?
sensitivity decreases, can cause you to eat more salt
hypertension risk
what tastes do newborns respond to? why is this relevant
dilute, sweet tastes
sweets can act as analgesics for newborns, has calming effect
where does analgesia from sweet tastes come from in newborns?
general brain arousal might be suppressed
most widely accepted mechanism is beta endorphin release, activating endogenous opiois system
PAG and raphe nucleus are immature still
can we link levels of sweetness to caloric value?
no, because of artificial sweeteners
long term effects are unknown
how can bitter taste be masked? at what level?
sodium salts: suppress bitter at level of bitter receptor
sugars: cognitive level
energy drinks and alcohol are stopped this way!
how does nucleus of the solitary tract process food?
receives multiple sensory inputs from vagus nerve
relays this info to viscera
reflex circuits that form basis for salivary secretions, mimetic responses, swallowing
how does central posterior medial nucleus of thalamus process food?
relay station for food perception
discriminative aspects of food!
how does gustatory cortex process food?
consists of insular taste cortex
operculum
post central gyrus
how do hypothalamus and amygdala process food?
emotion context of eating
memories of eating for amygdala
integrate homeostatic mechanisms such as hunger
interplay between eating and calming effects of food
how do orbitofrontal cortex process food?
integrate visual, somatosensory, olfaction, gustatory stimuli to appreciate food
what cells make up olfactory mucosa and bulb? what do they do
granular cells which increase specificity by releasing gaba
mitral and olfactory cells which project into olfactory tract
periglomerular cells which increase specificity, release gaba
olfactory neurons which synapse on glomeruli and release glutamate
how does anterior olfactory nucleus process olfaction?
relay station for ipsi and contralateral cortices
how does piriform cortex and lateral hypothalamus process olfaction?
control apetite and how olfactory input influences appetite and hunger
how does anterior cortical amygdaloid nucleus process olfaction?
emotional learning, olfactory fear conditioning
how does periamygdaloid cortex process olfaction?
integrate emotional aspect of food as elicited by odor
how does entorhinal cortex and hippocampus process olfaction?
memeory formation and how olfactory input facilitites memory and recall
connections within limbic and entorhinal cortex responsible for memory upon smelling odor!!
how is parkinsons relatd to the olfactory system?
neurons of olfactory among first to experience pathology , even before motor deficit
used as a biomarker for neurological disease!
