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olfaction-gustation.md
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## The chemical senses
* Chemical Senses
* Olfaction
* Taste
* Trigeminal chemosensory
* Irritant system
* smell (olfaction)
* phermones (vomeronasal)
* taste (gustation)
Note:
@@ -16,16 +14,16 @@ Mucus membranes of eyes face mouth
---
## Olfaction
## Olfactory system
* The olfactory system detects airborne molecules called odorants.
* Provides information about food, self, others, animals, plants, etc.
* Influence feeding behaviors, social interactions, and even reproduction.
* Processes information about the identity, concentration, and quality of a wide range of chemical stimuli.
* Detects airborne molecules called **odorants**
* Influences feeding behaviors, social interactions, and even reproduction
* Provides information about the identity, concentration, and quality of a wide range of chemical stimuli
Note:
* Provides information about food, self, others, animals, plants, etc.
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@@ -34,11 +32,11 @@ Note:
<div style="font-size:0.8em;">
<div></div>
* Starts in the nose, odorants bind to specific receptors found in the olfactory epithelium
* Olfactory epithelium projects to neurons in the ipsilateral olfactory bulb, which in turn sends projections contra and ipsi to the piriform cortex in the temporal lobe and other forebrain structures
* Piriform cortex is only 3-layered (sometimes called the archicortex), and is considered phylogenetically older than the neocortex
* Odorants bind to specific receptors on olfactory receptor neurons (ORNs) found in the dorsal epithelium of the nose
* ORNs project to the ipsilateral olfactory bulb, which in turn sends projections **directly to the cerebral cortex**, including the pyriform cortex, amygdala, and entorhinal cortex in the temporal lobe
* Pyriform and entorhinal cortex and amygdala is part of archicortex– phylogenetically older (and more simply layered) than the neocortex (6 layers)
* Unique among senses in that it does not include a thalamic relay between primary receptors and the cerebral cortex
* Piriform cortex relays information via the thalamus to the associational cortex to initiate motor, visceral, and emotional reactions to olfactory stimuli
* Pyriform cortex relays information via the thalamus to the associational cortex to initiate motor, visceral, and emotional reactions to olfactory stimuli
</div>
@@ -50,21 +48,28 @@ Note:
## Human olfactory bulb
<figure><img src="figs/Neuroscience5e-Fig-15.02-2R_a10bacf.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.2</figcaption></figure>
Note:
<!-- ## Rodent brain -->
---
## The flow of olfactory information
<div><img src="figs/nobelprize-org-2004-OR_7541302.png" height="400px"><figcaption>[nobelprize.org, 2004](http://www.nobelprize.org/nobel_prizes/medicine/laureates/2004/press.html)</figcaption></div>
<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>
<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
</div>
Note:
humans 12 million ORNS
rats 15 million ORNS
dogs 1 billion ORNS
---
@@ -75,6 +80,12 @@ Note:
Note:
The flow of olfactory information
<div><img src="figs/nobelprize-org-2004-OR_7541302.png" height="400px"><figcaption>[nobelprize.org, 2004](http://www.nobelprize.org/nobel_prizes/medicine/laureates/2004/press.html)</figcaption></div>
---
@@ -86,15 +97,12 @@ Note:
Note:
---
## Fun olfaction factoids
Fun olfaction factoids:
* Odors can be detected at very low concentrations (bell peppers 0.01 nM)
* Small changes in molecular structure can change perception
* Anosmics are people who cannot smell specific odors. 1/100 people cannot smell skunk, 1/10 hydrogen cyanide
Note:
---
@@ -149,11 +157,16 @@ alphabet
## The vomeronasal organ
<div style="font-size:0.8em;">
<div></div>
* Many species have a specialized structure that recognizes species-specific odorants called pheromones that play important roles in innate social, reproductive, and parenting behaviors
* The vomeronasal organ (VNO) projects to the accessory olfactory bulb, which in turn projects to the hypothalamus
* The VNO is absent or not very prominent in primates (including humans) and there is debate as to whether humans detect pheromones
* In animals a lesion in the main olfactory projection leaves reproductive behaviors intact, however lesions of the VNO projection severely compromises sexual selection and dominance hierarchies
</div>
Note:
rudimentary VNO found in 8% of adults. And VNO projects to special region of ob called accessory olfactory bulb which is also largely absent in primates.
@@ -178,26 +191,26 @@ Stowers, L.; Holy, T. E.; Meister, M.; Dulac, C.; Koentges, G. (2002). "Loss of
Note:
---
## Mouse pheromones
Record from a neuron in the AOB, pink area is when mouse is sniffing at face. Yellow are is when sniffing genitals.
<div><img src="figs/image1_9b348ce.png" height="400px"><figcaption>[Lou and Katz Science 2003](http://www.sciencemag.org/cgi/content/full/299/5610/1196/DC1)</figcaption></div>
Note:
---
## Human pheromones?
<div style="font-size:0.8em;">
<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
* 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
</div>
Note:
Human pheromones??
@@ -286,7 +299,7 @@ Humans have 23 pairs of chromosomes, while rats have 21 and mice have 20.
* Discovered by Linda Buck and Richard Axel. Shared nobel prize in 2004
* They found that olfactory receptors comprise a large GPCR gene family (~1000 olfactory receptors)
* Each olfactory neuron expresses a single olfactory receptor (even inactivates one copy of each allele)
* Each olfactory neuron expresses a single olfactory receptor
* Each receptor can bind to multiple odorants
* Each neuron that expresses a given receptor targets to the same glomeruli in the olfactory bulb
@@ -315,9 +328,8 @@ red arrows indicate intron locations of splice sites in other animals. Mammalian
largest single known gene family in all mammals. Representing 3-5% of genome. Perhaps 60% of these 950 OR genes are not transcribed in humans and chimps rendering them pseudogenes, vs 15-20% in mice and dogs.
pseudogene
: sequence of DNA containing a promoter and transcription initiation site, but due to sequence changes the DNA cannot be transcribed into a stable mRNA or the transcript cannot be translated into a protein.
pseudogene
: sequence of DNA containing a promoter and transcription initiation site, but due to sequence changes the DNA cannot be transcribed into a stable mRNA or the transcript cannot be translated into a protein
---
@@ -337,11 +349,7 @@ Note:
Note:
---
## ORNs are continuously generated from basal cells
ORNs are continuously generated from basal cells
* Turnover of 6-8 weeks in rodents
* Susceptible to pollutants, allergens...
@@ -349,9 +357,6 @@ Note:
<figure><img src="figs/Neuroscience5e-Fig-15.07-3R_copy_d15b3aa.jpg" height="200px"><figcaption>Neuroscience 5e Fig. 15.7</figcaption></figure>
Note:
basal cells and progeny in labeled in red
blue is all cell nuclei
@@ -427,16 +432,9 @@ Camphor is the smell of turpintine. Aromatic
Note:
---
## Olfactory system summary video
<div><video height=400px controls src="figs/Animation15-01TheOlfactorySystem.mp4"></video><figcaption>Neuroscience 5e Animation 15.1</figcaption></div>
Note:
---
## The olfactory bulb
@@ -452,15 +450,18 @@ ORNs that carry same olfactory receptors converge upon same glomeruli (Mombaerts
---
## Olfactory receptors are localized into discreet areas
## Localization preserved in the olfactory bulb
<div><img src="figs/image4_e4638ef.jpg" height="400px"><figcaption>Luo, Principals of Neurobiology</figcaption></div>
Note:
Olfactory receptors are localized into discreet areas
<div><img src="figs/image3_7693919.jpg" height="200px"><figcaption></figcaption></div>
<figure><figcaption class="big">olfactory cilia, all ORNs, I7 ORNs, M71 ORNs</figcaption><img src="figs/Neuroscience5e-Fig-15.10-0_copy_3bcd339.jpg" height="200px"><figcaption>Neuroscience Fig. 15.10</figcaption></figure>
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omp (green all ORNs). Adenylyl cyclase II (red) limited to olfactory cilia
all ORNs
@@ -470,21 +471,8 @@ I7 ORNs
M71 ORNs
---
## Localization preserved in the olfactory bulb
<div><img src="figs/image4_e4638ef.jpg" height="400px"><figcaption></figcaption></div>
Note:
* fig from luo principals of neurobiology?
---
## Subtle changes in a molecules structure can be detected by different receptors
<!--
Subtle changes in a molecules structure can be detected by different receptors
* Johnson, Woo, Hingco, Pham and Leon (1999) J. Comp. Neurol. 409:529
* n-amyl acetate, (control)
@@ -495,13 +483,11 @@ Note:
* Hexanoic acid, (6)COOH
Note:
* acid series of similar structures
* 2-deoxyglucose activation patterns in the rat olfactory bulb in response to an aliphatic acid series
* Johnson, Woo, Hingco, Pham and Leon (1999) J. Comp. Neurol. 409:529
* Johnson, Woo, Hingco, Pham and Leon (1999) J. Comp. Neurol. 409:529 -->
---
@@ -596,24 +582,18 @@ pathways
* Solitary nuclear complext to nucleus ambiguous to salivary glands
* Other somatosensory to parabrachial nuclei
---
## Cortical projections of gustatory pathway
Cortical projections of gustatory pathway
<figure><img src="figs/gustatorycentralpathways_2d4c5ae_copy_2f00775.jpg" height="400px"><figcaption></figcaption></figure>
Note:
* fig origin unknown.
From the VPM projections reach the gustatory cortex: anterior insular cortex and frontal operculum.
Information derived from different areas of the tongue is spatially segregated in the n. of the solitary tract, the thalamus, and the cortex. (Still true?)
---
## Gustatory cortex
Gustatory cortex
* Primary somatosensorycortex (Postcentral gyrus)
* Gustatory Cortex (frontal operculum andanterior insular cortex)
@@ -625,9 +605,6 @@ Information derived from different areas of the tongue is spatially segregated i
<div><img src="figs/gustatorycortex_52762a1_copy_ffa872c.jpg" height="100px"><figcaption></figcaption></div>
<div><img src="figs/gustatorycortexscheme_0fbbbe3_copy_d0e2238.jpg" height="100px"><figcaption></figcaption></div>
Note:
* fig origin unknown.
Note that the gustatory cortex is very close to the tongue area on the somatosensory cortex!
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* Taste receptors are organized in taste buds
* Taste buds contain between 30-100 taste cells
* 75% of all taste buds are found in papillae
* 3-types: fungiform (25%, localized in anterior tongue), circumvallate (50%, rear of tongue) and foliate (25%, posterolateral edge)
* There is great variability in the human population with respect to the number of taste buds
Note:
---
* 3-types: fungiform (25%, localized in anterior tongue), circumvallate (50%, rear of tongue) and foliate (25%, posterolateral edge)
## Tongue anatomy
Tongue anatomy
<figure><img src="figs/Neuroscience5e-Fig-15.18-1R_495eb15.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.18</figcaption></figure>
Note:
Types of papillae:
Circumvallatepapillae
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## Transduction mechanisms in a generic taste cell
<figure><img src="figs/Neuroscience5e-Fig-15.20-0_505080d.jpg" height="300px"><figcaption>Neuroscience 5e Fig. 15.20</figcaption></figure>
<figure><img src="figs/Neuroscience5e-Fig-15.20-0_505080d.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.20</figcaption></figure>
Note:
@@ -763,16 +738,10 @@ Note:
Note:
---
## Taste coding specificity and segregated representation
Taste coding specificity and segregated representation
<figure><img src="figs/Neuroscience5e-Fig-15.22-0_copy_8088d1f.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.22</figcaption></figure>
Note:
sweet a.a. and bitter receptors are expressed in diff subsets of taste cells.
gene from the TRPM5 channel is inactivated in ko mice and behavioral responses measured with taste preference test. Mouse gets two drinking spouts (one with water and one with tastant and relative frequency of licking is measured).
@@ -851,6 +820,3 @@ Note:
Note:
The orbital frontal cortex (OFC) receives inputs from vision, olfaction, and touch, as shown. It is the first area where signals from the taste and smell systems meet. (info based on E. T. Rolls (2000). The orbitofrontal cortex and reward. Cerebral Cortex, 10, 284-294, Fig. 2.)
---