Olfaction (Prof. Shaefer) Flashcards
What is the sense of smell ?
Why is it useful ?
Smell is the analysis of the chemical environment. This info is often useful to guide behaviour.
What makes small a special sense ?
We often have a hard time finding the words describing (or we don’t really know what we’re saying, e.g. “A brilliant composition, expressing NRG, light and virility, w/ the warmth of exotic woods.”)
Above all, smells evoke feelings, memories and behaviors.
What are pheromones ?
Pheromones are chemical substances produced and released into the environment by an animal, especially a mammal or an insect, affecting the behaviour or physiology of others of its species.
How does smell influence learnt and innate behaviors ?
It is useful to tell us if food is good or toxic, recognizing if a predator is approaching e.g. TTX (fox smell) scares miss/rats away.
It is also used for communication (pheromones between insects?).
Are natural scents more often uni- or multi-molecular ?
Multi-molecular e.g. the jasmine flower that releases 100s of odorant molecules.
How easily are mice trained to like/dislike certain odors ?
Pretty easily.
How do we often perceive smells in the environment ?
What do we make of this stimulus ?
Smell often comes w/ a great variety of odorants (many of which occur in complex pictures) and are often in the presence of background odors.
These stimuli have an impact on our innate and learnt behavior (some smells are naturally repelling, while we must learn that others imply danger or pleasure).
Our olfactory system uses these stimuli for scene segmentation, object recognition and learns to analyze some of these in great detail.
What are the various chemosensory system and what are they involved in ?
Main olfactory epithelium (MOE): mainly general odors, contains the olfactory sensory neurons (OSNs)
Gruenberg Ganglion: alarm/cold ?
Vomeronasal organ: mainly pheromones (perhaps some aspects of taste)
Septal organ: general odors/unclear
Where does the olfactory bulb (OB) project to ?
Mainly the amygdala, the hypocampal formation, the piriform cortex and the hypothalamus.
What is olfactory transduction and where does it happen
Olfactory transaction is the process whereby the chemical signal (odorant) is converted into a electrical signal (receptor potential). This happens in the olfactory cilia of the OSN in the MOE.
What are the steps of olfactory transduction ?
- The odorant molecule binds to the olfactory receptor GPCR
- Golf (the G-protoein associated w/ the receptor) dissociates, is dephosphorylated to G(alpha*) and activates adenylate cyclase
- ACIII* (adenylate cyclase type III) hydrolyses ATP to produces cAMP
- cAMP binds to CNGC (a cycle nucleotide gated Na+ and Ca2+ channel) and Na+ and Ca2+ enter the cell (depolarization)
- Ca2+ binds to CaCC (Ca2+ activated Cl- channel) and Cl- flow out of the cell (further depolarization).
How many functional odor receptor genes do humans have ?
What about mice ?
Humans have around 350 fctal receptor genes.
Mice have about 1000.
What is anosmia ?
Anosmia is the loss of the sense of smell. It is usually caused by a nasal condition or brain injury, but some people are born without a sense of smell (congenital anosmia). This is due to the lack of specific receptors.
How does the OR7DR (Olfactory Receptor type 7D4) show the diversity of the olfactory system ?
Subte changes in the OR7D4 GPCR can change the affinity of an animal for the molecules of androsterone and androstadienone.
RT (ArgThr) = more intensive “smell experience”
WM (TrpMet) = less offensive smell
Where do OSN converge in the OB ?
How is this organized ?
OSN converge to discrete glumuerli in the OB.
OSNs expressing the same genes, and thus w/ the same receptors, converge on a unique glomerulus.
