Quiz 4 - Brain Disorders - Olfaction, Taste, & Synesthesia

What is the accuracy and capacity of the human smell?

humans can recognize 10,000 different odors

65% accuracy after one year

women have better sense of smell

Does everybody smell odors in the same way?

NO

What is Olfaction?

the specialized sensory system responsible for the sense of smell

Olfaction bypasses what?

thalamus

Which sensory system bypasses the thalamus and sends signals directly to the cortex?

olfaction

Which sense is unique because its sensory information reaches the cortex without first relaying through the thalamus? bypasses thalamus unlike others

olfaction

What is the correct pathway for olfactory sensory information?

Olfactory receptor neurons → Olfactory bulb → Primary olfactory cortex

Any substance capable of stimulating the sense of smell by binding to an olfactory receptor is called?

odorant molecule

What are the requirements of odorant molecule?

volatile - must evaporate at room temp

at least slightly water soluble - to pass thru mucus layer

at least slightly lipid soluble - to pass through lipid membrane of cilia

ex) vanilla

Where is the olfactory epithelium located?

Upper posterior nasal passages

Approximately how many olfactory receptor cells are found in the olfactory epithelium?

100 million

The olfactory epithelium is best described as:

A small region only a few centimeters wide in the upper posterior nasal passages

What is covered by a mucous layer?

olfactory epithelium

Olfactory System Cell Type: Olfactory receptor neurons (ORNs)

bipolar sensory neurons; primary detector cells

Olfactory System Cell Type: Supporting (sustentacular) cells

support and maintain ORNs

Olfactory System Cell Type: Basal cells

undergo neurogenesis to replace ORNs (~every 40 days)

what sensory neurons in the nasal detect odorants and convert them into electrical signals

Olfactory receptor neurons (ORNs)

Which type of neurons in the adult mammalian brain undergo continuous neurogenesis?

Olfactory receptor neurons

Why can the olfactory nerve partially regenerate if damaged?

because olfactory receptor neurons undergo continuous neurogenesis

Olfactory receptor neurons are one of only ~3 adult mammalian brain structures that:

Undergo continuous neurogenesis

Can the olfactory nerve regenerate if damaged?

YES

What type of neuron are olfactory receptor neurons (ORNs)?

Bipolar neurons derived from the CNS

Which structure of the ORN detects odor molecules?

Cilia projecting from a mucosal knob

ORNs conduct signals slowly because their axons are:

Small and unmyelinated

How does the olfactory system encode different odors?

Each receptor binds multiple odorants; each odorant activates multiple receptors (combinatorial coding)

The thin section of bone that separates the nasal cavity from the brain and contains many small holes through which ORN axons pass to reach the olfactory bulb is called?

cribriform plate

a fractured cribriform plate would cause what?

CSF (Cerebrospinal fluid) leaking into the nose + loss of smell

from one nostril only (unilateral)

head trauma, surgery

The cribriform plate can serve as an entry point for which pathogen that destroys the olfactory bulb and frontal lobe surface?

***holes in the cribriform plate are a weak point as harmful pathogens can enter

Naegleria fowleri

Four Key Steps to Olfaction

Odorants bind to receptors

ORNs are activated

Signals are grouped by receptor type

Signals transmitted to cortex

ORNs travel through cribriform plate to reach olfactory bulb? And olfactory bulb sends information to cortex?

YES

What are the two multi-layered structures located on the ventral surface of the frontal lobes?

olfactory bulbs which are also parts of CNS

Olfactory bulbs contain what?

glomeruli & mitral cells

**these helps to send smell information to the cortex

Olfactory bulbs receive feedback from cortex because?

to modulate sensitivity, filter odors, and refine smell perception based on experience

wants it to re-smell to analyze more closely

1000 ORNs = ? increase sensitivity

1 mitral cell

Name level based on function: Odor identification and concentration; does NOT first pass through thalamus

Primary Olfactory Cortex

Name level based on function: Odor identification; reward value (pleasantness) of an odor

Secondary Olfactory Cortex

Name level based on function: Emotion and memory — ties odors to emotional memories

High-order processing

Blank is the key for olfactory perception:

• odor localization

• odor identification

• odor attention

“nasal ranger” research device to elongated nasal passages to study odor localization

Sniffing

Which cranial nerve provides a second set of sensory endings in the olfactory epithelium, detecting touch, pain, and temperature?

Trigeminal nerve (CN V)

What is true about trigeminal sensations from odorants?

~70% of odorants co-activate both the olfactory and trigeminal nerves

Where is Vomeronasal Organ located?

anterior nasal septum

What detects pheromones (external chemical signals)?

Vomeronasal Organ

may be considered lost/vestigial or integrated into main olfactory bulb

What is complete lack of ability to smell caused by trauma, dementia, nasal spray overuse, smoking, COVID-19 infection, etc.?

Anosmia

What is the decreased sensitivity of odors caused by clogged nasal sinuses from cold and/or nerve damage from trauma / infection?

Hyposmia

What is it called when things smell differently that they should (often unpleasant) due to hormonal changed in pregnancy, clogged sinuses, or nerve damage from trauma/infection?

Dysosmia

What is it called when sense of smell is abnormally acute (heightened) and associated with hormonal changes like pregnancy?

Hyperosmia

What is called “hallunicated smell”? perceiving an odor that is not present

Phantosmia

Phantosmia is a common cause of what?

seizure in temporal love epilepsy (unprovoked seizures)

Congenital Anosmia is present from birth? the person never experienced smell

YES

Congenital Anosmia is associated with what?

Kallmann Syndrome (delayed puberty + anosmia)

Acquired Anosmia is caused by what type of trauma?

deceleration injury (car accident)

Unilateral Anosmia is a type of acquired anosmia?

Yes, damage to one olfactory bulb → only noticeable if nostrils tested separately

What is the chemical sense that detects dissolved substances (tastants) in the mouth called?

taste (gastation)

sensory taste cells are among the…?

shortest lives cells in the body (~250 hours / ~10 days)

Do taste receptors cells regenerate? like skin cells

Yes

A young person’s mouth has approx how many taste buds

10,000

What signals carbohydrates / energy and has receptor mechanism of G-protein coupled receptor?

sweet

What signals sodium / electrolyte balance and has receptor mechanism of ion chemicals?

salty

What signals acidity / spoiled food detection and has receptor mechanism of ion channels?

sour

What signals potential toxins; triggers rejection and has receptor mechanism of G-protein coupled receptor?

bitter

What signals protein / glutamate (savory) and has receptor mechanism of G-protein coupled receptor?

umami

What is correct aka new model for taste map?

all tastes are represented across the entire tongue, some areas do have increased sensitivity

Tongue Anatomy: Fungiform Papillae

mushroom shaped

located mostly at apex (tip) and sides of the tongue

contains taste buds

Which part of the tongue is innervated by facial nerve (CN VII) and is visible as pink dots after blue dye staining

Fungiform Papillae

Do Filiform Papillae contain taste buds?

NO

Tongue Anatomy: Filiform Papillae

thin, long, V-shape cones

most numerous type

function: texture/friction/temperature

not involved in taste

Do Foliate Papillae contain taste buds?

YES

Tongue Anatomy: Foliate Papillae

ridges and groves on posterior lateral margins of tongue

innervated by CN VII (anterior) and CN IX (posterior)

Tongue Anatomy: Circumvallate Papillae

large; located at back on tongue in V-shaped row

contains many taste buds

Circumvallate Papillae in innervated by what nerve and how many per person?

3 - 14 per person Innervated by glossopharyngeal nerve (CN IX)

Molecules bind to what on taste receptor cells?

microvilli

what is microvilli?

microscopic, hair-like projections located on the surface of taste receptor cells within taste buds

fungiform papillae contain them

binding changes what?

receptor potential

Does taste go through thalamus?

Yes

Which cranial nerves carry taste information to the first central relay in the brainstem?

CN X → pharynx/throat

CN VII → anterior tongue

CN IX → posterior tongue

CN VII, CN IX, CN X

What is a a multisensory experience combining taste, smell (including retro-nasal smell through the back of the mouth), texture (S1), and sight called?

flavor

Supertasters have a higher density of what? more taste buds per square centimeter

fungiform papillae

Are Supertasters are more sensitive to umami taste??

No, more sensitive to bitter taste

What is the complete loss of taste called? These people cannot discriminate sweetness, sourness, bitterness, saltiness, or umami

Ageusia

What is the partial loss of taste; taste sensitivity is reduced?

Hypogeusia

What is the distortion or alteration of taste; food tastes abnormal?

Dysgeusia

What results from infection in the brain, nerve damage in the tongue, medication side effects, or vitamin deficiencies?

ageusia

A perceptual phenomenon in which the conscious experience of a stimulus attribute automatically leads to the conscious experience of an additional sensation

***When you consciously notice one part of a stimulus, it automatically makes you experience something extra, even though you didn’t directly sense it.

ex) Seeing a number as red because you always “feel” that number has a color

Synesthesia

1 in 23 to 1 in 200 have it

Is synesthesia genetic?

Yes, there is a strong genetic component — runs in families, diff family members may have diff types

What type of synesthesia is most common and well-studied where specific colors are seen for each letter/number; the trigger points are thus letter or numbers.

Grapheme-Color Synesthesia

What type of synesthesia is triggered by musical tones/sounds and associated with colors; colors are triggered by specific notes. ex) F major is pink sunset etc.

Sound-to-Color Synesthesia (Chromesthesia)

Which type of synesthesia is triggered by words or names which are associated with specific tastes; thought to involve increase connectivity between insula (taste) and temporal lobe (audiotory)

ex) “Derek” tastes like earwax

Lexical-Gustatory

What type of synesthesia is associated with a patient actually feeling the touch they observe?

Mirror-Touch Synesthesia

What type of synesthesia is associated with numbers, letter, days, and months being assigned personalities and/or genders.

ex) 4 is honest ; T are crabbed creatures

Ordinal-Linguistic Personification Synesthesia

What type of synesthesia is associated with numbers arranged in fixed spatial configuration in mind (automatic spatial map of numbers)

Number-Form (Spatial-Sequence) Synesthesia

Which type of synesthete experiences the synesthetic sensation as projected externally into space?

Projector Synesthete

Synesthetes..?

individuals with synesthesia

Which type of synesthete experiences synesthetic sensations as internal mental images “in the mind’s eye”?

Associator synesthete

A key difference between projector and associator synesthetes is:

Projectors perceive sensations externally; associators perceive them internally

Projector Synesthetes refelect changes in what?

early/lower-level sensory cortex

Is associator or projector syesthetes a prevalent/most common form of synthesia?

associator

Associator Synesthetes may refelect changes in?

higher-order associative cortex regions

Synesthesia is primarily considered a developmental condition because:

It results from decreased synaptic pruning during development

What is the consequence of reduced synaptic pruning in synesthetes?

Increased structural connectivity between normally separate brain areas