L30 - Smell and Taste Flashcards
Flavour is a mixture of what sensory inputs?
smell (olfaction)
taste (gustation)
tactile sensation (texture)
being chewed (mouthfeel)
Name and location of Receptors for smell?
olfactory receptors on the olfactory epithelium in the upper part of the nasal cavity
Describe the organization of olfactory chemoreceptor cells in the nasal cavity and olfactory bulb?
olfactory chemoreceptor cell in upper nasal cavity contains only one type of olfactory receptor
Each cells sends projections to the olfactory bulb through cribiform plate
> > All cells with a particular receptor converge on a precise region (olfactory glomerulus) in the olfactory bulb
Describe how odorant molecules in the air can lead to stimulation of olfactory chemoreceptor cells in the nose?
Odorant molecules diffuse to olfactory epithelium in nasal cavity
> > dissolve in mucus covering the epithelium
> > Bind to specific odrant receptors on the cilia of chemoreceptor cells
Describe how activated olfactory chemoreceptor cells transduce the signal to the olfactory bulb and lead to coding of odorant signal?
detection of a particular odorant
> > Increased conductance for Na+ and Ca2+ (due to second messengers generated from heterotrimeric G protein (Golf) activation)
> > depolarization of an olfactory chemoreceptor cell in a distinct combination/ pattern
> > all sensory cells with same receptor converge into same glomeruli in olfactory bulb
> > Specific glomeruli at specific locations in the bulb fire to produce ‘spatial map’ to secondary olfactory structures
Each odorant receptor expressed in the cilia of olfactory chemoreceptor cell can recognize all types of odrant molecules. T or F?
Each olfactory chemoreceptor cells only expresses one type of odorant receptor:
each receptor ONLY detects a small number of odorant molecules
How is the strength and quality of the odor processed in the olfactory bulb?
strength of the odorant = overall amount of afferent neuron activity
Spatial map/ patterns of neuron activity = coding olfactory information
What endogenous molecules can enhance the olfactory receptor neuron response?
Autonomic Modulation of Olfactory Signaling
Norepinephrine released by sympathetic nerves and acetylcholine released by parasympathetic nerves
> > Both enhance neuron response
(adrenergic and cholinergic modulation may also enhave olfaction)
What is the function of autonomic modulation of olfactory signalling?
Useful during stress or feeding:
- Stress: adrenergic stimulation enhances odorant contrast, filtering out weak responses and amplifying strongest and most salient olfactory cues
- Feeding: cholinergic modulation increases responses to many odorants > increase richness and complexity of olfactory cues
Impaired olfaction most commonly indicate what diseases?
neurodegenerative diseases, notably Parkinson’s disease and Alzheimer’s disease
List the five basic taste qualities?
Sweet, Umami, Bitter, Salty, Sour
What elicits the sensation of Umami flavor?
glutamate
serves as a flavor enhancer in the form of the additive monosodium glutamate (MSG)
Correlate each taste quality with their physiological function?
Sweet taste permits the identification of energy-rich nutrients,
umami allows the recognition of L-amino acids,
salt taste ensures the proper dietary electrolyte balance,
sour and bitter warn against the intake of potentially noxious and/ or poisonous chemicals
Taste receptors cells are neurons like olfactory receptor cells. T or F?
False
Taste receptor cells are not neurons, no axon itself
» Need to synapse with afferent neuron
List the papillae in the tongue?
Which has tastebuds?
- Filiform
- Fungiform
- Circumvallate/ Vallate
- Foliate
All have tastebuds except filiform
Function of filiform papillae?
Mouthfeel through somatosensory receptors
Spice signal is transduced by which cells of the tongue?
Not tastebuds
|»_space; rely on nociceptors
Taste signals are interpreted only at specific regions of the tongue in a “taste map”. T or F?
False
All areas of tongue can be excited by different tastes, not organized into maps
List the structures in the ‘olfacory cortex’ / secondary olfactory structures?
- Piriform cortex (exam)
- Amygdala
- Entorhinal cortex
Sequence of gustatory pathway?
Anterior 2/3 tongue = chorda tympani branch of facial nerve
Posterior 1/3 = Glossopharyngeal nerve
> > Taste afferent fibers end in Nucleus Solitarius
Parabrachial nucleus
VPM thalamus
Primary gustatory cortex (behind temporal lobe)
List the 2 opposing views of how taste qualities are encoded?
Labelled- line model
Across- fiber model
Describe the labelled line model of encoding taste signals?
each taste quality is specified by the activity of nonoverlapping cells and fibers
1 taste activates 1 type of taste-receptor cell» send one neuron to gustatory cortex
Describe the across fiber model of encoding taste signals?
2 possibilities:
1) Each individual taste-receptor cell tuned to multiple taste qualities»_space; 1 single afferent fiber carrying info for many tastes
2) Each taste-receptor cell tuned to one taste, but afferent fibers from the receptors converge and carry info for many tastes
Describe how food in mouth is trasnduced from taste into electrical signal?
• Chemicals from food dissolved in saliva
» contact the taste cells through the taste pore
- bitter, sweet and umami tastants bind to specific receptors on the microvilli of taste cells»_space; activate heterotrimeric G proteins
- Second messengers generated»_space; depolarization
- Depolarization of taste cells causes the release of neurotransmitters, which then stimulate neurons connected to the taste cells to relay electrical signals.
Define the tastants by the diff. modalities of activating taste cells?
Mediated by GPCRs T1R1, T1R2, T1R3:
- Sweet, umami , bitter
Mediated by ion channels:
- Salt, sour
List the GPCRs that mediate the different taste modalities?
Umami receptor: T1R1 + T1R3 heterodimer (exam)
Sweet receptor: T1R2 + T1R3 heterodimer (exam)
Bitter receptor: T2R
Describe the downstream signalling pathway from GPCR activation from different taste modalties?
[GPCR > PLC > IP3, DAG > TRPM5 > Taste cell depol.]
Tastants (sweet, bitter, umami) interact with specific GPCR receptors on microvilli of taste cells
activate heterotrimeric G proteins gustducin / Gαi2
> > release Gβγ subunits to stimulate phospholipaseC- β2 (PLC-β2)
> > generate IP3, DAG
> > gating of taste-transduction channel (TRPM5)
> > taste cells depolarize, release neurotransmitters
> > stimulate neurons connected to the taste cells to relay electrical signals
Describe the downstream reaction and receptors involved in transduction of salty and sour flavour?
act directly through ion channels to depolarize the taste cells
Salty receptor:
- low salt receptor = ENaC (epithelial sodium channel)
- High salt receptor: unclear
sour taste receptors:
- PKD2L1 (polycystic kidney disease 2-like 1 protein)
- OTOP1 (otopetrin 1)
How is taste quality and intensity interpreted in the brain?
Quality = ‘gustotopic map’ with distinct clusters of neurons in the gustatory cortex responding to bitter, sweet, salty, umami
+ somatosensory input for mouthfeel
Intensity = strength of afferent signal
Memory = whether the taste is pleasant or not
List some areas of the brain with overlapping activation to process flavour?
Gustatory cortex: insula, operculum,
+ orbitofrontal cortex + anterior cingulate
> > all responsive to tastant, odorant and somatosensory stimulation
