Physiology of olfaction and gustation Flashcards
What is ansomia
loss of sense of smell
What is aguesia
loss of sense of taste
What are tasants
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 is the sensory transduction in taste cells
specialized epithelial cells
chemosensory transduction is initiated on the apical domain and electrical signals are generated at the basal domain
TRansient receptor potential receptors (TRP) and Ion channels serve as the primary messengers
release of neurotransmitters
intracellular calcium release facilitiates the fusion and release of the neurotransmitters
Stimulus and neurotransmitter of Sour
Stimulus: H+ ions
neurotransmitter: serotonin
Stimulus and neurotransmitter for salty
Stimulus: Na+ binding ENaC
neurotransmitter: Serotonin
Stimulus and neurotransmitter for sweet
Stimulus: sugars binding GPCRs
neurotransmittter: ATP
Stimulus and neurotransmitter for Unami
Stimulus: Glutamate binding mGluR4 (GPCR)
neurotransmitter: ATP
Stimulus and neurotransmitter for Bitter
Stimulus: various compounds binding GPCR
Neurotransmitter: ATP
Sensory Transduction in olfactory neurons
Bipolar cells that release glutamate
odorant binds a odorant specific G protein (Golf) which activates a adenylate cyclase producing cAMP thus opening a (CNGC) cation channel allowing for the influx of Na+ and Ca+ this then opens a Ca+ and Cl- channel which allows for Cl- out of the cell further depolarizing the cell
What happens as a odor persists
as an odor persists sensitivity of the CNGC to cAMP decreases reducing the cation influx all due to enzymatic activity
or a odorant receptor gets phosphorylated over time to become adapted to the smell
Hyposima
thickened mucus blocks the odorant receptors making it harder to smell things
What are the nutritional values for each taste: Sweet
sweet signals the presence of carbohydrates that serve as an energy source
What are the nutritional values for each taste: Salty
Salty taste governs the intake of Na+ annd other salts essential for maintaining the bodys water balance and blood circulation
What are the nutritional values for each taste: Umani
Umani is generally believed to reflect a foods protein content due to the presence of glutamate and other amino acids
What are the nutritional values for each taste: Sour
sour taste signals the presence of dietary acids
spoiled foods often are acidic and thus avoided
What are the nutritional values for each taste: Bitter
thought to gaurd against consuming poisons
since it is so important these bitter tuned GPCR bind with high affinity compared to other taste receptors and need for low concentration to better prevent ingestion of poisons
What happens to gustatory and olfactory sensitivity with age
Declines with age
therefore adults eat food with more salt and spices which can be problematic for individuals that have hypertension and or electrolyte issues
What is the significance of sugar with infants
babies are primed to the taste of amniotic fluid which reflects the composition of the maternal diet and therefore helps localize the rooting for breastmilk after birth
however newborns respond to sweet tastes and will cause relaxation and decreased heart rate of the infant therefore sweet tastes act as a analgesics if the infant has to do minor painful procedures
this is thought to activate the endogenous opioid system (beta endorphin release)
How does sugar help with taking medicine
Most medicines taste bitter to an individual and trigger the bitter receptors
however masking with sodium salts (monosodium glutamate and sodium gluconate) suppress bitter taste at the level of the receptor
Sugar suppresses the bitterness at the cognitive level
what is the function of the Nucleus of the solitary tract
receives multiple sensory inputs from vagus nerve that relays information about the viscera. Early site of gustatory and visceral information . reflex forms basis for salivary secretions, mimetic responses and swallowing
what is the function of the ventral posterior medial nucleus of the thalamus
relay station for taste perception. The discriminitive aspects of taste are processed here
what is considered the gustatory cortex
Insular taste cortex, operculum of the frontal lobe, post central gyrus
What is the function of the hypothalamus and the amygdala
affective aspects of eating, emotional context to eating, memories of eating (amygdala)
Integration of homeostatic mechanisms of eating like hunger (hypothalamus)
Interplay between eating and the calming effects of food take place in the limbic and reward system
What is the function of the orbitofrontal cortex
Integrating visual, somatosensory, olfaction and gustatory stimuli to collectively appreciate the flavor of food
What is the perception of flavor
requires gustatory input, olfactory input, and somatosensory information which come together in the medial orbitofrontal cortex
what is the function of the Anterior olfactory nucleus
Relay station to the ipsilateral and contralateral corticies
What is the function of the priform cortex and the lateral hypothalamus
control of appetite and how olfactory input influences appetite and hunger
What is the function of the piriform cortex and the medial orbitofrontal cortex
integration of sight, smell, and taste of food. appreciation of the flavor of food
What is the function of the anterior cortical amygdaloid nuclei
emotional learning, olfactory fear conditioning
What is the function of the periamygdaloid cortex
integration of the emotional aspect of food as elicted by odor
What is the function of the entorhinal cortex and the hippocampus
memory formation and how olfactory input facilitates both memory and recall
connections within the limbic system and entorhinal cortex are responsible for highly evocative experience of memory upon odor sensation
What are the layers of the olfactory bulb
olfactory epithelium
cribiform plate
GLomerular layer: contain olfactory glomerulus and periglomerular cells which release GABA to specify the signal
External plexiform layer: contain tuft cells which project to olfactory tract
Mitral cell layer: mitral cells that project to the olfactory tract
Granule cell layer: contain granule cell which release GABA to help specify the signal
Olfactory tract
(superior)
What is the significance of loss of smell and neurodegenerative disease
Loss of smell has been shown as early prognosis of individuals with Parkinson disease
Olfactory testing is used as a biomarker for early diagnostic testing against neurodegenerative diseases
