3.0 Olfaction and Taste Flashcards
What is the role of the olfactory epithelium?
Detects airborne odorants
What is the role of the nasal turbinates?
1) Enlarge olfactory epithelium<br></br>2) Improve airflow contact
How do odorants dissolve in the mucus film?
In association with odorant binding protein
How often are olfactory receptors renewed?
Every 60 days (by basal cell division)
What are the steps for olfactory transduction?
Olfactory receptor (on cilia) → Golf → AC → ↑cAMP → opens cyclic nucleotide gated cation channels (inflow of <b>Ca²⁺</b> + Na⁺) → depolarization
What can augment depolarisation in olfactory transduction?
Cl⁻ outflow through Ca²⁺ gated channels
How does olfactory adaptation occur?
Ca²⁺ also works on calmodulin to ↓ sensitivity of cation channels to cAMP
How is calcium extruded from the cell in olfactory cells?
NCX
What is the pathway of transmission of olfactory information?
Olfactory receptors axons pass through cribiform plate to olfactory bulb<br></br><br></br>Olfactory receptors → <b>Mitral cells</b> + tufted cells → <b>Lateral olfactory tract</b>
What mediates lateral inhibition in the olfactory bulb?
Periglomerular and granule cells
Define lateral inhibition:
Stimulation of a neuron leads to inhibition of an adjacent receptor through an inhibitory neuron
What 5 regions in the cortex does the lateral olfactory tract synapse with?
<b>1) Anterior olfactory nucleus</b> - mediates inhibition between 2 bulbs via anterior commisure<br></br><br></br><b>2) Olfactory tubercle</b><br></br>- Projects to medial dorsal nucleus of thalamus → orbitofrontal cortex<br></br>- Mediates conscious perception of odour<br></br><br></br><b>3) Pyriform cortex</b><br></br>- Projects to other olfactor cortical regions<br></br><br></br><b>4) Amygdala</b> - Affective component/ emotion <br></br><br></br><b>5) Entorhinal cortex</b> - Affective component/ emotion
What is the vomeronasal organ?
Projects via accessory olfactory bulb to amygdala<br></br>Mediates response to pheromones
What are trace amine associated receptors?
Found in human main olfactory epithelium<br></br>Detect volatile amines in sweat → shifts mood/fertility
What are the three papillae with taste buds?
Circumvallate<br></br>Fungiform<br></br>Foliate
What are the different taste qualities?
1) Bitter<br></br>2) Sweet<br></br>4) Umami<br></br>5) Salt<br></br>6) Sour
What are the different taste receptor cell types?
1) Receptor cells (Bitter, sweet, umami)<br></br>2) Presynaptic cell (Sour [acid])<br></br>3) Glial like cell (salt)
What are the specific receptors for Umami, sweet and bitter?
Umami = T1R1 + T1R3<br></br>Sweet = T1R2 + T1R3<br></br>Bitter = >30 T2R
What is the transduction mechanism for Umami, sweet and bitter?
GPCR activation → βγ translocation → IP₃ → ↑ Ca²⁺ release from intracellular storage → opening of TRP5M cation channel → depolarisation<br></br><br></br>Depolarisation + ↑ intracellular Ca²⁺ → neurotransmitter release
What is the transduction mechanism for sour?
Mechanism not fully known. Involves intracellular acidification of receptor.<br></br><br></br>K⁺ channels blocked by protons → depolarisation → opening of Ca²⁺ channels → transmitter release
What is the transduction mechanism for salt?
Na⁺ entry (via epithelial sodium leak channels) → depolarisation
Taste afferents in chorda tympani, glossopharyngeal and sup. laryngeal nerves proceed via cranial nerves ______________ to synapse in the _____________ of the __________ within the gustatory nucleus. In the primate, an uncrossed pathway projects to the ______________________ of the thalamus, and then to _____________________ in the ______________________. From primary taste cortex, projections pass to the secondary taste area in ______________________, where units modulate their discharge according to the pleasantness of the taste of food, and to the _____________, which plays a role in the affective component of taste response. Projections to the _______________ modulate feeding behaviour. In subprimate species (rodents) the _________________ runs via a __________________ in the _____________, where changing physiological conditions may modify feeding behaviour.
Taste afferents in chorda tympani, glossopharyngeal and sup. laryngeal nerves proceed via cranial nerves <b>VII, IX and X</b> to synapse in the <b>solitary nuclear complex</b> of the <b>medulla</b> within the gustatory nucleus. In the primate, an uncrossed pathway projects to the <b>ventral posterior medial</b> nucleus of the thalamus, and then to <b>gustatory neocortex</b> in the <b>anterior insula and frontal operculum</b>. From primary taste cortex, projections pass to the secondary taste area in <b>orbitofrontal cortex</b>, where units modulate their discharge according to the pleasantness of the taste of food, and to the <b>amygdala</b>, which plays a role in the affective component of taste response. Projections to the <b>lateral hypothalamus</b> modulate feeding behaviour. In subprimate species (rodents) the <b>thalamocortical pathway</b> runs via a <b>pontine relay</b> in the <b>parabrachial nucleus</b>, where changing physiological conditions may modify feeding behaviour.
What is across-fibre code?
Individual fibres respond to a range of stimuli, but tend to prefer just one of these. Therefore taste is identified by the pattern of afferent activity evoked in different fibres
What type of input do afferent taste fibres receive?
Tuned input.<br></br>1) From receptor cells via <b>ATP</b> released across <b>gap junction hemichannels</b><br></br>2) From presynaptic cells via <b>serotonin</b>
