Olfaction* Flashcards
Types of chemoreception?
Olfaction and gustation
Links between taste and smell - processing? regulation?
Both are associated with memory and emotion
Reduced taste without smell, as there is a crossover in the processing of the senses
Taste and smell can also regulate GI secretion
Process of olfaction - nose to brain?
Odorant molecules enter the nose and then become dissolved in the nasal mucus, which is transmitted to the olfactory neurons and terminating in the olfactory bulb. output from the olfactory bulb projects via olfactory tracts to both ipsi- and contralateral regions of the olfactory cortex
Olfactory neuron activation?
Odorant molecules bind to the cilia of the olfactory neurons, this leads to a transduction process via g-prot 2nd messenger
7 different smell categories?
peppermint, musk, floral, ethereal, pungent, putrid and camphoraceous
Reason for why you can localise smell?
Olfactory pathways from the nose project directly to cortex. Bi-directional projections (nostrils) give rise to smell localisation.
Structure of an olfactory receptive neurone?
Soma
Dendrite
Knob
Cilia
Signal transduction of an activated olfactory neurone?
Odorant molecule binds to the odorant receptor leading to gprot activation and activation of AC, which catalyses cAMP. cAMP act Ca chs leading to Ca and Na influx and depol. Depol leads to Cl act, letting Cl out of the cell.
However, there is a feedback system to return back to mem potential. Ca binds calmodulin reducing affinity of Ca ch for cAMP, and activates CaM kinase phosphorylation AC and reducing cAMP production.
Na/Ca exchanger to remove Ca from cell, relieving the stim effect on the Cl ch and allowing Cl to return to normal.
Special characteristic of the olfactory receptive neurone? + lateral inhibition
Each ORN only express the same odorant receptor
Binding leads to AP and propagation to olfactory bulb
Each different ORN receptor type segregate from other types and become a glomeruli-like branching system
Stimulated glomeruli and mitral cells can laterally inhibit adjacent through periglomerular and granule cells
Convergence of olfactory signals - differentiation? sharpening of the odour code?
Achieved by lateral inhibition of more weakly activated glomeruli
Dampening the mitral cells of adj glomeruli
Stronger glomeruli have synchronised firing of mitral cells, leading to summation in the olfactory cortex (receive more inputs
Called the sharpening of the odour code
How is topography achieved - olfactory bulb? inhibitory ligands? axons?
Gradient of inhibitory axon guidance ligands are often established in the olfactory bulb
Extent of incoming axons invaded the bulb depends on the axon’s sensitivity to the inhibitory ligands (receptor number)
Axons with less receptors pass further into the bulb
Topography is achieved by axons originating from the same area managing to project to complementary positions in the target.
Vomeronasal organ - pheromones?
Ephrins
Topographical system may underlie the accurate olfactory axon projections to the olfactory bulbs.
Plasticity of olfaction - loss of smells?
Activated odorant circuits complete out inactive ones
Loss of a channel in the ORN
Still project, but can’t be stimulated
Inactive ORNs were eliminated and leaving only the active ORNs
If you don’t use it, you’ll lose it
Taste sensation and the brain?
Taste is linked to memory and moods due to dynamic sensory processing in the brain.
Parabrachial and nucleus of the solitary tract in brainstem
