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olfaction-gustation.md
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Note:
phylogenetically oldest sense.
Phylogenetically oldest sense.
not considered very important in humans compared to other senses, but think about the fantastically strong emotional memories tied to smells— the olfactory system when robustly stimulated can have much influence over the formation of olfactory tied memories through its direct connectivity to the limbic and memory systems of the brain. We’ll learn a bit about this connectivity later.
While it is not considered very important in humans compared to other senses, the olfactory and gustatory systems play a powerful role in influencing the behavior of animals including ourselves. Think about the fantastically strong emotional memories tied to smells— the olfactory system when robustly stimulated can have much influence over the formation of olfactory tied memories through its direct connectivity to the limbic and memory systems of the brain. We’ll learn a bit about this connectivity later.
Mucus membranes of eyes face mouth
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## Human olfactory bulb
<figure style="width:500px; float:left; margin:0 20px"><img src="figs/Neuroscience5e-Fig-15.02-2R_a10bacf.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.2</figcaption></figure>
<figure style="width:500px; float:left; margin:0 20px"><img src="figs/Neuroscience5e-Fig-15.02-2R_a10bacf.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.2; Human brain ~20cm length; rat brain ~3cm length</figcaption></figure>
<div style="width:400px;float:left;font-size:0.7em;">
<div></div>
species | olf bulb surface area (cm<sup>2</sup>)
--- | ---
human | 10
rat | 15
cat | 20
dog | >150
species | olf bulb surface area (cm<sup>2</sup>) | number of olfactory receptor neurons
--- | --- | ---
human | 10 | 1.2x10<sup>7</sup>
rat | 15 | 1.5x10<sup>7</sup>
cat | 20 |
dog | >150 | 1.0x10<sup>9</sup>
</div>
@@ -71,6 +69,22 @@ humans 12 million ORNS
rats 15 million ORNS
dogs 1 billion ORNS
human brain: 20cm long
rat brain: 3cm long
---
## Dogs smell better than humans
<figure><img src="figs/Neuroscience5e-Fig-15.02-1R_copy_cf5395a.jpg" height="200px"><figcaption>Neuroscience 5e Fig. 15.2</figcaption></figure>
<figure><img src="figs/Neuroscience5e-Fig-15.03-0_copy_398483b.jpg" height="200px"><figcaption>Neuroscience 5e Fig. 15.3</figcaption></figure>
Note:
<div><video height=400px controls src="figs/Animation15-01TheOlfactorySystem_OC.mp4"></video><figcaption>Neuroscience 5e Animation 15.1</figcaption></div>
---
## Organization of the human olfactory system
@@ -92,8 +106,7 @@ The flow of olfactory information
## Olfactory perception
* Is not as acute in humans as in a number of other animals
* Less acute in humans because of a smaller variety of functional olfactory receptor proteins, less receptor neuron density, and also a lesser amount of relative cortex used to process information
* Mice have ~1000 olfactory receptor genes, humans several hundred
* Less acute in humans because of less receptor neuron density and also a lesser amount of relative cortex used to process information
Note:
@@ -138,6 +151,12 @@ butyl mercaptan: similar to major constituent of defensive spray in skunk
tert-butyl mercaptan: natural gas additive
D-limolene (citrus): humans can smell at 15 molecules per billion
ozone: 10 molecules per billion
small molecular changes can matter to odorants: D-carvone smells like spearming, L-carvone smells like caraway seeds in rye bread
---
## Combinatorial coding
@@ -205,7 +224,7 @@ Record from a neuron in the AOB, pink area is when mouse is sniffing at face. Y
<div></div>
* Female rodents (mice) grouped together synchronize their estrous cycle upon exposure to pheromones in male mouse urine (‘Whitten effect’). This depends on pheromone receptors and VNO—>AOB connectivity.
* VNO is vestigial in humans: VRs and TRPC2 are pseudogenes
* VNO is vestigial in humans
* Myth: women who live in close proximity synchronize their menstrual cycle (the ‘McClintock effect’, after McClintock, Nature 1971). The current scientific evidence for this effect in human is not strong.
* However there’s some evidence for odorants working as pheromone-like molecules to influence behaviors (attraction, fear) mediated by the main olfactory system
@@ -217,6 +236,8 @@ Human pheromones??
vestigial. VNO anatomy is non-functional in human.
TRPC2 are pseudogenes in human.
myth of mcclintock effect. statistical issues with these studies, no one has reported human estrous cycle synchrony over more than 6-9 months as indeed the original study was on college women at wellsey over the period of one academic calendar year. Windshield wiper, coupled oscillator analogy. Just out of phase.
But other animals…
@@ -311,16 +332,10 @@ Linda Buck and Richard Axel "for their discoveries of odorant receptors and the
## Olfactory receptors
<figure><img src="figs/Neuroscience5e-Fig-15.09-1R_copy_3521e8e.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.9</figcaption></figure>
Note:
---
## Olfactory receptors
<figure><img src="figs/Neuroscience5e-Fig-15.09-2R_copy_fde3d57.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.9</figcaption></figure>
<div style="float:left">
<img src="figs/Neuroscience5e-Fig-15.09-1R_copy_3521e8e.jpg" height="300px"><figcaption>Neuroscience 5e Fig. 15.9</figcaption>
<img src="figs/Neuroscience5e-Fig-15.09-2R_copy_fde3d57.jpg" height="300px"><figcaption>Neuroscience 5e Fig. 15.9</figcaption>
</div>
Note:
@@ -340,6 +355,17 @@ pseudogene
Note:
---
## Olfactory receptor signal transduction
* Binding of odorant to receptor activates a Gα (Called G-olf) that in turn activates adenylyl cyclase
* cAMP gates a Na+/Ca2+ cation channel. Calcium rushes in and activates a Cl- channel. Chloride normally high in-low out in olfactory neurons and thus Cl- leaving also depolarizes cell
Note:
---
## ORN receptor potentials generated in cilia
@@ -363,17 +389,6 @@ blue is all cell nuclei
green for OMP at right
---
## Olfactory receptor signal transduction
* Binding of odorant to receptor activates a Gα (Called G-olf) that in turn activates adenylyl cyclase
* cAMP gates a Na+/Ca2+ cation channel. Calcium rushes in and activates a Cl- channel. Chloride normally high in-low out in olfactory neurons and thus Cl- leaving also depolarizes cell
Note:
---
## Olfactory receptor signal transduction
@@ -422,18 +437,6 @@ Eucalyptol is cineole
Camphor is the smell of turpintine. Aromatic
---
## Dogs smell better than humans
<figure><img src="figs/Neuroscience5e-Fig-15.02-1R_copy_cf5395a.jpg" height="200px"><figcaption>Neuroscience 5e Fig. 15.2</figcaption></figure>
<figure><img src="figs/Neuroscience5e-Fig-15.03-0_copy_398483b.jpg" height="200px"><figcaption>Neuroscience 5e Fig. 15.3</figcaption></figure>
Note:
<div><video height=400px controls src="figs/Animation15-01TheOlfactorySystem_OC.mp4"></video><figcaption>Neuroscience 5e Animation 15.1</figcaption></div>
---
@@ -503,7 +506,7 @@ Subtle changes in a molecules structure can be detected by different receptors
Note:
* fig origin unknown. No find through image search
* todo
---
@@ -705,17 +708,6 @@ Composite fMRI image showing different locations of activation in insular cortex
Note:
---
## Transduction mechanisms in a generic taste cell
<figure><img src="figs/Neuroscience5e-Fig-15.20-0_505080d.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.20</figcaption></figure>
Note:
---
## Taste receptors
@@ -729,6 +721,27 @@ Note:
Note:
---
## Transduction mechanisms in a generic taste cell
<figure><img src="figs/Neuroscience5e-Fig-15.20-0_505080d.jpg" height="500px"><figcaption>Neuroscience 5e Fig. 15.20</figcaption></figure>
Note:
amiloride sensstive ant channenels for salt
h+ sens trip channel for sour
T1R2-T1R3 g protein recept for sweet
T1R1T1R3 g proteain recep for umami with trpM5 IP3 Ca2+ channels
T2R gprotein for bitter with TRPM5 ca2+ channel
---
## Taste receptors