34- Anatomy of the Nose (4.17.26)

Anatomy of the Nose

4.17.26

Slido

Announcements

• Exam 3 due next Wed 4/22 at 11:59 pm

• Additional Zoom lecture available for content from last Monday (4/13)

What was the last thing you intentionally smelled?

Anatomy of the Nose

https://youtu.be/0xcLbPkzN9w?si=WDViUO94I3ILSgPs

Pathways of the Nasal Cavity

Orthonasal pathway: odorant molecules enter the nasal cavity through the nostrils Retronasal pathway: odorant molecules enter from the oral cavity through the pharynx

Pathways of the Nasal Cavity

Turbinates: bony convolutions that disperse air evenly throughout the nasal cavity

Olfactory Receptor Neurons (ORNs)

Olfactory receptor neurons (ORNs) are found in the olfactory epithelium

• ORNs have olfactory receptors that respond to odorant molecules in the air
• Each ORN dies after a few weeks and is replaced by a new cell
• Basal cells become the new ORNs

Olfactory Receptor Neurons (ORNs)

• Olfactory receptor neurons (ORNs) have hair-like cilia that project into the mucus layer

• Each ORN has only one type of receptor

• Each cilium has multiple receptors for a particular type of odorant molecule to bind to

Olfactory Transduction

How olfactory transduction occurs:

• Binding to receptors in the cilia opens ion channels that allow sodium & calcium to enter

• If enough ion channels are open at a particular moment in time, voltage-gated channels open and the ORN fires an action potential

Mitral & Tufted Cells

• mitral & tufted cells serve as relay neurons within the glomeruli in the olfactory bulb

• their axons form the olfactory tract (carries neural signals from the olfactory bulb to higher areas of the brain)

Glomeruli

• glomeruli: where the olfactory receptory neurons (ORNs) meet the mitral cells and tufted cells

Bowman's glands

• Bowman's glands secrete mucus to catch odorants

• mucus also blocks irritants and microorganisms from penetrating the central nervous system

• mucus is swallowed & regenerated every 10 min

Neural Code for Odor Discrimination

A given olfactory receptor neuron (ORN) will respond to a range of different odorant molecules, but to varying degrees based on fit/preference

Neural Code for Odor Discrimination

Which combination of ORNs are active, and how strong that activity is, provides a population code for a wide range of odors

Here, the mouse would perceive these odors as distinct (but all foul-smelling)

Neural Code for Odor Discrimination

• You can get a different pattern of population responses from the same odor at different concentrations.

• “Chemotopic” organization: organized according to the chemical odorants being detected

Thank you so much for listening!

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Next class: Finishing up the olfactory system