Physiology of Olfaction and Gustation Flashcards
(35 cards)
Sour
Stimulus: H+
NT: serotonin
Salty
Stimulus: Na+ binding ENaC
NT: serotonin
Sweet
Stimulus: sugars binding GPCRs
NT: ATP
Umami
Stimulus: glutamate binding mGluR4
NT: ATP
Bitter
Stimulus: various compounds binding GPCRs
NT: ATP
What type of cells are taste buds
specialized epithelial cells
How is chemosensory transduction initiated in taste buds?
- initiated in apical domain
- electrical signals generated at the basal domain via graded receptor potentials and release of NT
Where are taste receptor proteins located?
concentrated in the microvilli that emerge from the apical surface
What types of cells are olfactory cells?
bipolar neurons that release glutamate
Steps in olfactory sensory transduction
1) odorant in mucus binds to receptor in membrane of cilia
2) activates Golf protein
3) activates adenylate cyclase
4) generation of cAMP
5) opens ion channel to let in Na+ and Ca2+
6) depolarization
7) opening of Ca2+ and Cl- channels open to provide remainder of depolarization needed to generate receptor potential
How is receptor potential reduced in olfaction transduction?
- enzyme breakdown when cAMP levels drop
- binding of calcium to calmodulin reduces affinity for channel to cAMP
What occurs when a robust smell is perceived?
- odorant becomes phosphorylated, which modifies its sensitivity to odorants
- reduces cation influx
- adaptation
Give an example of reversible hyposmia
-when you have a cold, thickened mucus blocks odorants from binding the odorant receptor
Which tastes binds with the highest affinity to their GPCR?
bitter; to detect poison
What occurs when dilute sweet tastes are given to infants?
- analgesia
- pleasure
- only effective in oral
- activates descending pain modulation centers in rats
- sweet taste induced beta-endorphin release which activate the endogenous opioid system
How does sodium block bitter taste?
suppresses at level of bitter-receptor
How does sugar block bitter taste?
suppresses at cognitive level
Role of nucleus of solitary tract in gustation
- receives sensory input from vagus that relays info from viscera
- reflex circuits form basis for salivary secretions, mimetic responses and swallowing
Role of ventral posterior medial nucleus of thalamus in gustation
- relay station for tastes perception
- discriminative aspects of taste processed here
Which areas comprise the gustatory cortex?
- insular taste cortex
- operculum of frontal lobe
- post central gyrus
Role of amygdala in gustation
-affective aspects of eating, emotional context of eating, memories of eating
Role of hypothalamus in gustation
-integration of homeostatic mechanisms of eating
Role of limbic system in gustation
-interplay between eating and the calming effects of food
Role of orbitofrontal cortex
-integrating visual, somatosensory, olfaction and gustatory stimuli to collectively appreciate the flavor of food
