BIOL 4380 Lecture Notes - Lecture 10: Piriform Cortex, Orbitofrontal Cortex, Bloodhound
13 May 2018
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• How do we know that the bub innervates all of these structures? From FMRI studies.
The front section is the orbitofrontal cortex, then the pyriform cortex and then the amygdala.
Smells that are pleasant, light up the orbitofrontal cortex, whereas other intense smells will
activate the pyriform cortex and the amygdala. There are no clear topographic maps of olfactory
information in the CNS.
• Odorant perception in mammals:
o Humans have the least ORNs, compared to dogs and even rats.
o The number of ORNs is’t related to the size of the rai. I dogs, the loodhoud has
the greatest number of ORNs. these dogs were bred to sniff!
o On the x axis here, you can see the surface area of the olfactory epithelium which is
proportional to the number of ORNs.
• Despite the fact that humans have so few ORNs compared to bloodhounds, we are
capable of smelling things surprisingly well. Humans can track smells over long distances, just
like dogs. They are ee apale of learig ho to trak sets, if they’re traied. After only 5
days of training, the speed with which a human can track a scent, increases by 3-5 fold and the
mean deviation from the track decreases (both dogs and humans, would track using a jagged
trajectory. Why is this type of path used by an animal? An animal uses the concentration of
set as a ue to figure to the diretio. Whe the aial goes aay fro the soure, it’ll go
back to the source.
• There are a couple of chemicals which humans are amazingly sensitive to: ozone and D-
lioee. We’re apable of detecting ozone at about 10 molecules in a billion. Why is this so,
evolutionarily? Ozon is extremely poisonous in high concentrations. D-limonene we can detect
tie as uh → itruses.
• Chemical indole smells floral and smells putrid at high concentrations. A molecule that is
basically identical to its mirror image: L-carvone (smells like caraway), D-carvone (spearmint).
• Depending on whether the smell is pleasant or unpleasant, the orbitocortex lights up for
pleasant smells.
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Document Summary
The front section is the orbitofrontal cortex, then the pyriform cortex and then the amygdala. Smells that are pleasant, light up the orbitofrontal cortex, whereas other intense smells will activate the pyriform cortex and the amygdala. There are no clear topographic maps of olfactory information in the cns. Humans have the least orns, compared to dogs and even rats. The number of orns is(cid:374)"t related to the size of the (cid:271)rai(cid:374). I(cid:374) dogs, the (cid:271)loodhou(cid:374)d has the greatest number of orns. these dogs were bred to sniff! On the x axis here, you can see the surface area of the olfactory epithelium which is proportional to the number of orns. Despite the fact that humans have so few orns compared to bloodhounds, we are capable of smelling things surprisingly well. Humans can track smells over long distances, just like dogs. They are e(cid:448)e(cid:374) (cid:272)apa(cid:271)le of lear(cid:374)i(cid:374)g ho(cid:449) to tra(cid:272)k s(cid:272)e(cid:374)ts, if they"re trai(cid:374)ed.
