Lecture 50: Taste & Smell Flashcards
(28 cards)
Name the chemical senses:
Gustation and olfaction
What are the roles of chemical senses?
- Sample food/drink for nutrient content, palatability, toxicity
- Generate sensory perceptions to ingested and inhaled chemicals
- Guide appetite, trigger processes for
absorbing nutrients - Avoid poison and chemical hazards
- Avoid predators
- Find a mate
What are chemical senses stimulated by?
Chemicals either in the air we inhale (odours) or in food/drink (tastes)
What chemical types can our taste receptors detect?
- Sweet
- Sour
- Salt
- Bitter
- Umami (meaty/savoury/MSG)
How many odorant receptor types do we have and how many are “pleasant”?
~1000 but only 20% are pleasant
How many taste buds do we have?
2000-5000
Where are taste buds located?
- Mostly on the tongue, but also in palate, pharynx, and epiglottis
- Taste buds are clustered in papillae
- watch slide
What do taste cells detect?
Tastants
-Type II and III cells
How do tastants act?
Dissolve in saliva and act on taste receptors at the taste pore
How often do taste cells turn over?
~20-30 days
How many stimulus does each taste cell usually have?
1
What is the modality of type ll taste cells?
GPCR chemoreceptors for sugar, amino acids (umami), or bitter stimuli
What is the modality of type lll taste cells?
Na+ or H+ sensitive cation channels
Describe the process of taste transduction for type ll taste cells:
- Stimulated by sugars and sugar-like molecules
- Activation of T1R receptor complex (sweet and umami) or T2R (bitter)
- Depolarisation and activation of afferent gustatory nerve via atypical non-vesicular ATP release via CALHM1/3 channels
- AP initiated at afferent nerve
Describe the process of taste transduction for acid on type lll taste cells:
- H+ enter via cation channel (Otop1)
- electrochemical gradient
- change in intracellular pH blocks K+ leak - Combined effect of positive charge influx and blocked of K+ outflow depolarise cell
- Activation of voltage-gated Ca2+ channels
- Vesicle release of serotonin (5-HT) onto afferent gustatory nerve fibre to initiate AP
Describe the process of taste transduction for salt on type lll taste cells:
- Na+ enter via cation channel (ENaC)
- electrochemical gradient - Depolarise cell
- Activation of voltage-gated Ca2+ channels
- Vesicle release onto afferent gustatory nerve fibre and initiate AP
Describe the taste pathway:
- Taste receptors activate cranial nerves VII (facial), IX (glossopharyngeal), and X (vagus)
- Synapse onto 2nd afferent neurons in the nucleus of solitary tract of medulla
- Cross-inhibition can occur for sensory contrast and enhancement
- Primarily ipsilateral pathway - Synapse onto 3rd afferent neurons in thalamus
- Neurons project to gustatory cortex for taste sensation and perception
- Chemotopic organisation
Why are many qualities of food not true taste sensations?
Stimulating chemicals do not interact with specific oral taste receptors
How is spiciness sensed?
By heat and pain nerve fibres
* Capsaicin (chilis) activates TRPV1
* Piperine (pepper) also activates TRPV1
* Menthol (minty) activates TRPM8
What occurs to odorants during olfaction?
- Inhaled and swirled around in nasal conchae
- Dissolve in watery mucus in roof of nasal cavity
- Detected by cilia projecting from olfactory sensory neurons
Describe the process of signal transduction for olfaction:
- Odorant molecules bind to specific GPCRs on cilia of olfactory sensory neuron
- Activation of cAMP and opening of ion channels
- Na+ and Ca2+ influx leads to
depolarization (graded potential) - Threshold -> AP initiated at axon hillock
Name 3 structures in the olfactory pathway (olfactory bulb)
Glomeruli, mitral cells and tufted cells
What is the glomeruli?
Spherical clusters of synaptic input and dendritic architecture, encapsulated by glia
What are the mitral and tufted cells?
Encode odor identify and intensity (2nd afferent neurons)
