L10 - Gustation & Olfaction Flashcards
5 sensory stimuli and 1 new one is
Acid, bitter, sweet, salt, umami (MSG) AND fatty acid
Where are fatty acid receptors found in mouth
in palate, upper part roof of mouth
Why is fat so delicious?
Odorants are dissolved into fats - Olfaction via diffusion of volatie odorants into nasal cavity
Where are taste buds found?
In papilae
How long do taste cells and olfactory cells take to turn over (make new cells)?
2 weeks
T/F: Taste cells in a single taste bud have different sensitivites
True
Tip of tongue is used for which taste
Sweet
How do the 5 sensory stimuli depolarise taste cell
Salt - Na+ ions depolarize taste cell via amiloride sensitive Na channels
Acid - H+ ions depolarize via H+ channels
Sweet, Umami and Bitter (G-protein coupled) - alpha-gustducin (G-protein to phospholipase C and hence to depolarising mechanisms (IP3 -> Ca2+)
*TRPM5 channel (menthol receptor that allows Ca2+ influx as well - related to capsaicin)
Specifics about sweet, umami, bitter receptors
Sweet and Umami have > 1 receptor
- each operate via a heterodimer receptor
- Sweet (T1R2/T1R3)
- Umami (T1R1/T1R3) - these receptors respond to glutamate, enhanced by inosine
Bitter (T2R - taste number 2 receptor)
Pannexin channel?
Recent argument that release is not via vesicle release but through this channels that opens gaps in the cytoplasm to allow NT to go into extracell. space
List of taste cell transmitters
Serotonin, glutamate, ACh, Noradrenaline, GABA (usually inhibitory but excitatory in these cells), ATP
Where do gustatory afferents synpase?
In gustatory nucleus, part of solitary nucleus of medulla (ipsilateral projection)
Central taste pathways
Perception mediated via gustatory projection to ventral posterior medial nucleus of thalamus -> primary gustatory cortex (insula and frontal operculum)
Where is the olfactory epithelium found?
On roof of nasal cavity
Whats different from olfactory receptor cells and taste cells turn over?
Olfactory receptor cells have the same rate of turn over but olfactory receptor cells send axons through Cribiform plate to the olfactory bulb
Olfactory transduction
G-protein coupled receptor (G olf/ alpha - transducin) a trimer -> activated by odorant -> increase cAMP in cell -> acts on cAMP dependent Na+ channel -> depolarization
Also lets Ca2+ in -> activating Cl channel -> Cl- exit cell -> depolarizing it
Where are the olfactory receptors found?
On the cillia
In a current trace, a downward deflection = ___, voltage trace is opposite
Depolarization
Does specifity of odor detected occur in olfactory bulb or cortex?
Bulb
Structure of olfactory bulb
Projection neurons (1 class called mitral cell) are second order olfactory neurons that have branching dendritic trees that form glomeruli with terminals of olfactory receptor cells. Individual glomeruli encode only one odour. Granule cell neurons (similar to amacrine cells in visual system) act as tuning interneurons that leads to output.
T/F: Individual glomeruli encode only one odour.
True
T/F: Receptor cells that synapse on a particular glomerulus all have the same receptive field (express the same odorant receptor)
True
Central olfactory pathways
Olfactory receptors -> olfactory nerve -> Projection neurons of olfactory bulb -> olfactory tract -> olfactory bulb targets (Pyriform cortex, olfactory tubercle, amygdala, entorhinal cortex) -> Orbitofrontal cortex, thalamus, hypothalamus, hippocampal formation
