Odorants

Question 1

How is the olfactory system a prime example of pharmacology

Answer 1

involves an interaction b/t chemical substances and tissues

Question 2

Dual requirement of the olfactory system:

Answer 2

• Recognizing and consciously distinguishing a very wide variety of odorants.
• Initiating subconscious responses to pheromones

Question 3

Olfactory sensory neurons are found in the

Answer 3

olfactory epithelium

Question 4

Pathway for odours (general structures)

Answer 4

olfactory sensory neurons (in olfactory epithelium) –> main olfactory bulb (MOB) –> olfactory cortex

Question 5

Role of olfactory cortex

Answer 5

conscious perception and emotional and motivational responses via amygdala and hypothalamus

Question 6

Primary olfcatory neurons are….

Answer 6

constantly differentiated from epithelium throughout life

Question 7

Primary olfactory neurons break from the belief that…

Answer 7

neurogenesis doesn’t occur in adults, as the nasal epithelium can differentiate to form primary olfactory neurons in adults

Question 8

Pheromone response pathway

Answer 8

Vomeronasal organ (VNO) –> accessory olfactory bulb (AOB) –> amygdala and hypothalamus –> pheromone responses (work primarily through IP3 system)

Question 9

The nomeronasal organ is ___ in animals where pheromones play a larger role

Answer 9

bigger

Question 10

Specific pathway (of cell types) of odours

Answer 10

OSNs –> glomeruli –> mitral cells –> cortex

Question 11

Ordorant receptors properties

Answer 11

• have 7-transmembrane domaines (in olfactory G-protein–Galpha olfactory)
• 1% genomic
• ~1000 genes code for ORs
• ORs have diverse structures

Question 12

Pheramone receptors props

Answer 12

V1R and V2R
~185 types identified
also 7-TM (like odorant receptors)

Question 13

All odorants evoke…

Answer 13

the same specific effect i.e. depolarization of olfactory sensory neurons (ONS)

Question 14

Individual ORs recognize ___ ordorants therefore are relatively _______ (selective/non-selective)

Answer 14

Can recognize MULTIPLE ordorants

NON selective

Question 15

Each OSN expresses ___ type(s) of OR

Answer 15

ONLY 1 type;

BUT note that that one OR can recognize many different odorants

Question 16

Information from receptors to brain–chemical signalling pathway

Answer 16

G-alpha-olf –> adenylyl cyclase III–> increases cAMP –> opens cyclic nucleotide gated cation channels –> depolarization

Question 17

Each OSN has

Answer 17

a single axon going to the olfactory bulb

Question 18

___ OSN axons go to each glomerulus

Answer 18

several thousands

Question 19

OSN to glomerulus to mitral cell ratios

Answer 19

All axons of OSN expressing a given odorant receptor

converge on the same glomerus –> one mitral cell

Question 20

What is the likely cause of the high sensitivity of the olfactory system

Answer 20

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

Question 21

OR selectivity

Answer 21

not super selective, electrophysiological response to many compounds
less strong = less selective for that compound
More strong = the specific compounds of that OR

Question 22

OR family used in a combinatorial function to encode identities of different odors because

Answer 22

• individual ORs recognize multiple odorants
• individual odorants recognized by multiple receptors
• different odorants detected by unique combinations of OR’s
define ordorants in combo

Question 23

What allows for the wide variety of orders perceived–thought experiment

Answer 23

• 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

Question 24

Each smell has a…

Answer 24

distinct Spatial Representation in Olfactory Bulb that is projected to Olfactory Cortex
different pattern = different smell

Question 25

Central processing of odours–in glomeruli

Answer 25

• 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)

Question 26

what aspect of the olfactory system mimics the visual system

Answer 26

the olfactory system dissects components of an odor and reassembles it in olfactory cortex, similar to visual
system

Question 27

How do we get odor preception in short:

Answer 27

• 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

Question 28

Complex ordors usually perceived as distinct ______

Answer 28

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