4. Olfaction

Question 1

What are Odors?
• Mixture of molecules (odorants)
• Volatile molecules- ____, aldehydes, ____
• Natural odors contain hundreds of odorants
• Smell of particular molecules differ depending on ____

Answer 1

acids
ketones
concentration

Question 2

Role of olfaction

• Locating ____
• Marking territory
• ____
• Detecting predators and threats
• ____
• Role in taste and flavor

Answer 2

food
reproductions
suckling

Question 3

Anatomy

• Coronal section of your face going through your nose and orbits.
• In humans you have your nasal septum in the middle, then you have your superior, middle,
and inferior turbinates.
• You have nasal mucosa that covers all of these areas, and as you probably know these are ____ epithelium that humidifies and warms that air as you breathe it in.
• The point of the turbinates/conchae is to create some ____ and allow it to get to your olfactory nerve.

Answer 3

ciliated respiratory

air turbulence

Question 4

Anatomy

• A closer view of that in a CT scan. Anytime you see a CT scan you should always describe the view. This is a coronal view of a bone window CT scan.
• These are CT scans of a deer and lemur that really show the ____ of their nasal turbinates and a large part of why other animals can smell a lot better than us.
• They have a lot more ____ to be able to detect odorants.

Answer 4

complexity

surface area

Question 5

Olfactory pathway

• In terms of anatomy you should know its part of your olfactory nerve, then it goes to your olfactory ____, ____, and then back to your brain in the olfactory ____.

Answer 5

bulb
tract
cortex

Question 6

Anatomy

• More anatomy. The olfactory nerve and bulb rests in the ____ portion of your anterior cranial fossa.
• This is the area at the very top of your nasal cavity where you have your sense of smell.
• If you think about when you are actually trying to smell something what do you tend to do? You sniffle, sniff it up into your nose, you try to create more turbulence and concentrate the
odorants to go up into your nasal cavity up into this region so that you can smell it a little bit better.

Answer 6

anterior

Question 7

Anatomy

• Again, just another close up in terms of the olfactory bulb and the sensory neurons that are traveling through your ____, and innervating basically the ____ portion of your nasal mucosa.

Answer 7

cribiform plate

superior

Question 8

Anatomy

• Just a picture of the olfactory bulb and tract as it goes on the ____ surface of your brain.

Answer 8

ventral

Question 9

Anatomy

• Just a picture of different regions in your brain that are pretty important for the sense of smell. The olfactory cortex is primarily made up of your ____ cortex, your ____ cortex, as well as your ____ gyrus is important as well.

Answer 9

primary olfactory
piriform
parahippocampal

Question 10

How are odors detected?

• How are odors detected? You guys should know that as I said its about a 3 cm by 3 cm region on the ____ portion of your nasal mucosa where these cells reside.
• These are olfactory sensory neurons, they are your typical ____ cells with an axon and a dendrite. Basically each of these bipolar cells has about 5-20 cilia on each of the dendrites.

• You can see here this is basically mucous that lines your respiratory epithelium. That is created by ____ cells and ____ glands that secrete a mucous onto your mucosa.

• Each particular olfactory sensory neuron detects one molecule of an odorant or one particular type of odorant. These cells turnover pretty quickly and they are replaced every ____ weeks and they are preformed from ____ cells, which are like your epidermis.
• These olfactory sensory neurons come through the cribriform plate and the axons then come up to your olfactory bulb and synapse there.

Answer 10

superior
bipolar
goblet
bowman
6-8
basal

Question 11

G protein-coupled receptors

• These particular odorants they bind to the olfactory sensory neurons by your typical g-protein coupled receptors that you have learned about.
• Causes transformational changes, release of ____ that then causes the sodium calcium channels and chloride channels to ____, causes nerve depolarization, propagation of action potentials, and transference of basically neural understanding or whatever.
• Its basically pretty much how most nerve function works and propagates through your system.

Answer 11

cAMP

open

Question 12

Olfactory Sensory Neuron

• As he said before, each olfactory sensory neuron detects ____ type of odorant.
• Say these odorants are colors. So there’s a “red” odor and basically all of these here that are red all sense that one particular molecule.
• Whats interesting is that each of those axons project onto one particular ____ on the
olfactory bulb. So all the red odors project to a particular part of the olfactory bulb around these particular glomeruli. The blue ones go to the blue glomeruli.
• Thats where they then synapse with your mitral and tuften cells (???) and then that information gets pass along further into your brain. As we said before most odors are made up different types of molecules – and numerous hundreds of molecules and types of molecules – so it basically creates like a ____ map on these olfactory bulb that your brain senses and then can identity pretty much a particular type of odor.
• For humans you can based upon these types of patterns and whatnot we can typically sense around 10,000 different types of odors on average.

Answer 12

glomeruli

spatial

Question 13

Olfactory bulb

This is your olfactory epithelium (He starts with left picture I assume). The axons going down to those particular glomeruli, the blue ones the red ones the green ones.
• And then you have your second order neurons that are your ____ and ____ cell layers that basically then their axons form and coalesce and become the olfactory ____ that goes back to the brain.

• There are lots of different types of cells that help to support this whole system. Some of these cells are inhibitory like ____ cells (?), granules cells, and inhibition of this is also very important because you don’t necessary want to be overstimulated by every single molecule or sense of smell.
• So pretty much only the ____ senses of smell and nerve propagation are able to pass through to your brain for perception.

• (Right picture I believe) This is just a cross section of all of this. This is your epithelium and then you have your glomerular layer here, and then basically it just correlates to the different layers that are on this side here as well (left image).

Answer 13

mitral
tufted
tract

para-follicular
smaller

Question 14

Olfactory Tract

• Bundle of axons from ____ and ____ cells from the olfactory bulb
• The olfactory tract is basically the bundle of axons from your mitral and tufted cells that go from the olfactory bulb and then synapse in the sensory portions of your brain.

Answer 14

mitral

tufted

Question 15

Olfactory pathway and cortex

• This slide is busy but shows the same thing. The different areas of your brain that sense olfaction.
• These ____ and ____ cells become the tract (orange dot).
• They go to different areas of your brain: olfactory ____, ____ cortex, ____ too.

• There’s this vomeronasal organ (circled) that is not particularly developed in humans but more
so in animals that goes towards your amygdala, that has a lot to do with your ____ drive and sense of emotions as well. So perhaps that’s why ____ don’t work as well as in humans as they do in other animals.

Answer 15

mitral
tufted

tubercle
piriform
amygdala

sex
pheromones

Question 16

Olfactory Cortex

• The mitral/tufted cells going to different portions of your brain.
• The primary olfactory cortex is mostly your olfactory ____. This pathway is not particularly
well understood. The brain is poorly understood in general. Smell is not well understood.
• They just kind of know that these are the particular regions that are involved with smell based upon ____.

• Its interesting that the olfactory cortex– there’s also an understanding of higher ____ that also impact your understanding and your sense of smell. There are some study’s that show if you’re smelling a strawberry and if you are seeing a picture of something that is red then you smell it stronger than if you were not seeing red.
• Theres a lot of interplay between all the sensations that you have and your perception and understanding of that particular odor or smell.

Answer 16

tubercle
fMRI’s
cortices

Question 17

Piriform Cortex
• Different from all other sensory cortex. Receives information from 2nd order neurons (mitral and tufted cells), not from the ____.
• Non-____, unlike the olfactory bulb
• Anterior and Posterior Piriform Cortex
o Odor ____, constancy, and categorization

• The piriform cortex receives information from the mitral and tufted cells. Most sensory nerves – second order neurons synapse onto your thalamus, which is kind of like your relay center for most sensation.
• But for smell for whatever reason most of that doesn’t happen and the second order neuron binds ____ to your cortex.
• The piriform cortex is thought to have odor identity, constantsy, categorization where you are able to identify specific odors, make and have an understanding of differences between odors and identify them.

Answer 17

thalamus
topographic
identity

directly

Question 18

• Another important part of this process is the synapses with your amygdala. The amygdala does have a lot to do with ____ emotions and memory, which is important in terms of smell. If you guys know what things smell good and what things smell bad and then you react to them.
• Its important for animals to know that this particular odor is associated with something that is trying to eat me.
• Thats all he said.

Answer 18

remembering

Question 19

Orbitofrontal Cortex

• Mediates ____ perception of odor
• Integrates smell and taste to create ____

• Orbitofrontal cortex is in this particular area (arrow) and mediates your conscious perception of odor, and integrates smell and taste allows you to understand it a little bit better.

Answer 19

conscious

flavor

Question 20

Odor Adaptation/Fatigue

• Inability to smell an odor after ____ exposure
• Necessary to prevent sensory ____
• Decreased response to a ____ stimulus
• At level of olfactory neuron, ____ represses opening of cation channels, inactivates adenylyl cyclase, and allows ____ of cAMP
• Odor adaptation and fatigue. You know when you walk into a room that smells really bad – if you stand in that room that smell kinda goes away after a while, or at least your brain doesn’t really sense it after prolonged exposure. This is the explanation for that.
• Its to prevent sensory overload. At the level of the neuron there are some repressing of these channels and do not allow continuous neural propagation of those odors.

Answer 20

prolonged
overload
constant
Ca2+/calmodulin-dependent protein kinase II
breakdown

Question 21

• Whole point of the jelly bean thing is to show how important smell is to your ____. He gave out jelly beans and had people pinch their nose to see the change of effect. Its hard to tell what flavor of jelly bean it is without smell.

Answer 21

taste