Odorants Flashcards
How is the olfactory system a prime example of pharmacology
involves an interaction b/t chemical substances and tissues
Dual requirement of the olfactory system:
- Recognizing and consciously distinguishing a very wide variety of odorants.
- Initiating subconscious responses to pheromones
Olfactory sensory neurons are found in the
olfactory epithelium
Pathway for odours (general structures)
olfactory sensory neurons (in olfactory epithelium) –> main olfactory bulb (MOB) –> olfactory cortex
Role of olfactory cortex
conscious perception and emotional and motivational responses via amygdala and hypothalamus
Primary olfcatory neurons are….
constantly differentiated from epithelium throughout life
Primary olfactory neurons break from the belief that…
neurogenesis doesn’t occur in adults, as the nasal epithelium can differentiate to form primary olfactory neurons in adults
Pheromone response pathway
Vomeronasal organ (VNO) –> accessory olfactory bulb (AOB) –> amygdala and hypothalamus –> pheromone responses (work primarily through IP3 system)
The nomeronasal organ is ___ in animals where pheromones play a larger role
bigger
Specific pathway (of cell types) of odours
OSNs –> glomeruli –> mitral cells –> cortex
Ordorant receptors properties
- have 7-transmembrane domaines (in olfactory G-protein–Galpha olfactory)
- 1% genomic
- ~1000 genes code for ORs
- ORs have diverse structures
Pheramone receptors props
V1R and V2R
~185 types identified
also 7-TM (like odorant receptors)
All odorants evoke…
the same specific effect i.e. depolarization of olfactory sensory neurons (ONS)
Individual ORs recognize ___ ordorants therefore are relatively _______ (selective/non-selective)
Can recognize MULTIPLE ordorants
NON selective
Each OSN expresses ___ type(s) of OR
ONLY 1 type;
BUT note that that one OR can recognize many different odorants
Information from receptors to brain–chemical signalling pathway
G-alpha-olf –> adenylyl cyclase III–> increases cAMP –> opens cyclic nucleotide gated cation channels –> depolarization
Each OSN has
a single axon going to the olfactory bulb
___ OSN axons go to each glomerulus
several thousands
OSN to glomerulus to mitral cell ratios
All axons of OSN expressing a given odorant receptor
converge on the same glomerus –> one mitral cell
What is the likely cause of the high sensitivity of the olfactory system
Because so many OSN axons, all carrying information from the same type of receptor, converge on each
glomerulus –> high sensitivity
therefore few cells firing in response to a few molecules of odorant may be enough to activate a glomerulus
OR selectivity
not super selective, electrophysiological response to many compounds
less strong = less selective for that compound
More strong = the specific compounds of that OR
OR family used in a combinatorial function to encode identities of different odors because
• individual ORs recognize multiple odorants
• individual odorants recognized by multiple receptors
• different odorants detected by unique combinations of OR’s
define ordorants in combo
What allows for the wide variety of orders perceived–thought experiment
- If each odorant were recognized by 3 of the possible 1000 OR’s
- # of possible combinations = 1000^3 = 10^9
- 10^9 different odors could be perceived
I.e. the combo of receptors activated allows for a wide range of orders to be perceived
Each smell has a…
distinct Spatial Representation in Olfactory Bulb that is projected to Olfactory Cortex
different pattern = different smell
Central processing of odours–in glomeruli
• Specific groups of glomeruli in specific places in olfactory bulb activated by various odors –> Spatial representation of each odor in the olfactory bulb –> projected to cortex (where spatial representation is maintained)
what aspect of the olfactory system mimics the visual system
the olfactory system dissects components of an odor and reassembles it in olfactory cortex, similar to visual
system
How do we get odor preception in short:
• Each odorant activates unique set of receptors
• Activates a unique set of glomeruli
• Stimulus reconstructed in olfactory cortex which
determines which glomeruli have been activated
Complex ordors usually perceived as distinct ______
odor objects
the combo of these objects determines what the odorant is
allows you to smell any smell as it is made of of measurable components that you can reassemble
