C8 - CHAPITRE 12-13 Flashcards
What are the three main domains of olfaction’s function?
Warning, nutrition, and social communication.
What is the role of smell in protecting the body?
It screens air and food, allowing us to hold our breath or stop ingesting harmful substances.
What are microbial threats detected by smell associated with?
The basic emotion of disgust (e.g., mold, spoiled food).
What are non-microbial threats detected by smell associated with?
The basic emotion of fear (e.g., smoke, predator body odor).
How does smell help with food detection?
It helps us detect and identify food sources.
How does smell relate to food expectancy?
It detects violations of flavor expectations (e.g., blue cheese taste in a chocolatine).
How does smell regulate food intake?
It helps us monitor quantity and quality of what we eat.
What role does smell play in breastfeeding?
It contributes to mother-infant bonding and feeding behavior.
In what ways does smell contribute to social communication?
It helps us evaluate partner fitness, perceive emotions, and avoid incest.
Is olfactory social communication conscious or unconscious?
Mostly unconscious.
What are the two types of sensory interactions with the environment?
Physical interactions (e.g., hearing, seeing) and chemical interactions (e.g., smelling, tasting).
In physical senses like hearing and vision, how does the stimulus interact with the sensory cells?
The stimulus source doesn’t directly touch the receptor cells; it transmits energy (like light or sound waves) across a distance.
In chemical senses like smell and taste, how does the stimulus interact with sensory cells?
The chemical stimulus must enter the body and interact directly with receptor cells.
How does vision work as a physical sense?
Photons from a light source hit a surface, reflect, enter the eye, stimulate retinal receptor cells, and produce an action potential.
How does smell work as a chemical sense?
A portion of the odor source enters the nose and interacts with olfactory receptor cells.
How does taste work as a chemical sense?
Gustatory stimuli are dissolved in saliva and interact with taste receptor cells.
Describe the process of hearing as a physical sense.
Sound vibrations from a source (e.g., vocal cords) are transferred through air, vibrate the eardrum, then stimulate inner hair cells, which send action potentials to the brain.
Why are hearing and seeing considered non-contact senses?
Because the stimulus source does not directly touch the sensory receptors (e.g., vocal cords and inner ear, or light and retina).
How far can a light source be and still be perceived?
For example, the sun is 150 billion meters away, yet its light is perceived through photons.
What triggers the perception of smell?
When volatile chemical substances (odorants) interact with olfactory receptor cells in the olfactory epithelium and the signal reaches the olfactory cortex.
Where is the olfactory epithelium located?
In the upper portion of the nasal cavity.
What are odorants?
Volatile organic or some inorganic compounds with certain carbon chain lengths that can evoke smell perceptions.
Give examples of odorants and their associated smells.
Vanillin (4-hydroxy-3-methoxybenzaldehyde) → vanilla
Benzaldehyde → almonds
2-phenyl-ethanol → roses
Hydrogen sulfide (inorganic) → rotten eggs.
Are smells usually caused by single molecules?
No, they are usually caused by mixtures of many odorants.
What is an example of a smell made of many molecules?
Coffee odor contains hundreds of different molecules.
What does the smell of cola mainly consist of?
A mixture of lime, cinnamon, and vanilla.
Why is it difficult to identify individual components in a smell mixture?
Because the sense of smell is synthetic, meaning it integrates all components into a single perception.
What happens when a new odorant is added to a mixture?
It can change the smell of the entire mixture.
When do we tend to notice odors in the air?
Only when the concentration of a given odorant increases rapidly.
What condition must be met for an odorant to evoke a smell sensation?
The odorant must enter the nose.
How does the entrance to the nose compare to a Gothic cathedral?
Like a cathedral with a grand facade and small doors, the nostrils are small relative to the nose’s overall structure.
What divides the nasal cavity?
The nasal septum, which usually is not exactly midline, creating two asymmetrical nasal passages.
What are the turbinates?
Three bony structures on the lateral walls of the nasal cavity (upper, middle, lower) that increase surface area and are covered with respiratory epithelium.
What are the functions of the respiratory epithelium in the nose?
To warm, clean, and humidify the air going to the lungs.
Where is the olfactory epithelium located?
In the uppermost portion of the nasal cavity, stretching from the olfactory cleft to the middle turbinate.
What is orthonasal olfaction?
Smelling from outside the body, where odorants enter through the nostrils (e.g., smelling coffee or flowers).
What is retronasal olfaction?
Smelling from inside the body during eating, where odorants from food in the mouth reach the nasal cavity via the pharynx.
Why is retronasal olfaction important?
It is crucial for flavor perception and allows us to distinguish between different foods like pineapple and apple.
Why does food taste bland when we have a blocked nose?
Because odorants cannot reach the olfactory epithelium, impairing retronasal olfaction, which is responsible for most flavor perception.
What tastes can the tongue detect without involving smell?
Sweet, sour, bitter, salty, and umami.
How can you test the importance of retronasal olfaction?
Pinch your nose while eating a candy or food item. Once you release your nose, the flavor perception increases dramatically.
What distinguishes the olfactory epithelium from respiratory epithelium?
It contains olfactory receptor cells (olfactory sensory neurons) in addition to supporting cells and glands.
What part of the olfactory receptor cell reaches into the nasal cavity?
The dendritic knob and cilia, which are embedded in mucus.
Where are the olfactory receptors located?
On the membranes of the cilia of olfactory receptor neurons.
What happens when an odorant binds to an olfactory receptor?
It triggers an intracellular cascade that leads to depolarization and generates a nerve impulse.
Where is the first cerebral relay station of the olfactory pathway?
The olfactory bulb, specifically in structures called glomeruli.
What forms the olfactory nerve?
The axons of all olfactory receptor cells.
How many functioning olfactory receptors do humans have?
About 300–400 different types.
How does the number of olfactory receptors in humans compare to dogs and mice?
Dogs (~1,000) and mice (~1,200) have more than humans.
How many receptor types does each olfactory receptor neuron express?
Only one type per neuron.
What determines the response of an olfactory receptor?
The physico-chemical properties of the odorant (e.g., functional groups like hydroxy-groups).
What’s an example of a receptor detecting a functional group?
A receptor that responds to hydroxy-groups may detect alcoholic notes in odors.
Are receptor neurons organized in the olfactory epithelium?
No, they are randomly distributed.
How is organization achieved in the olfactory bulb?
Neurons with the same receptor type converge onto the same glomerulus.
How does the brain identify different smells?
By detecting specific patterns of glomerular activation, based on receptor combinations.
Why can we distinguish billions of odors?
Because of the nearly infinite permutations of glomerular activity patterns.
Which cells receive input from olfactory receptor neurons in the glomerulus?
Mitral cells in the olfactory bulb.
What do the axons of mitral cells form?
The olfactory tract.
Where do mitral cell axons terminate?
In the primary olfactory cortex via the olfactory triangle and lateral olfactory stria.
Name the key regions that make up the primary olfactory cortex.
Anterior olfactory nucleus, Olfactory tubercle, Piriform cortex, Entorhinal cortex, Amygdala, Hippocampus.
Which secondary olfactory areas are involved in further processing?
The insular cortex and the orbitofrontal cortex.
What is unique about the lateralization of olfactory information processing?
It is mainly ipsilateral (processed on the same side), unlike other senses.
Does the olfactory pathway involve a mandatory thalamic relay?
No. It bypasses the thalamus, although some connections to the thalamus exist.
How does the olfactory cortex differ from other primary sensory cortices?
It is not exclusively dedicated to olfaction; it also includes structures from the limbic system involved in emotion, learning, memory, and reward.
What is the Proust effect?
A phenomenon where smells evoke vivid and emotional autobiographical memories, often unconsciously.
Which structures in the olfactory pathway contribute to the Proust effect?
The amygdala, hippocampus, and other limbic system components.
Which literary work inspired the naming of the Proust effect?
Marcel Proust’s ‘À la recherche du temps perdu (In Search of Lost Time)’, where the narrator is overwhelmed by memories upon tasting a Madeleine soaked in tea.
What percentage of the population is affected by olfactory disturbances?
Up to 20%.
What are the two main categories of olfactory dysfunction?
Quantitative and qualitative dysfunction.
What percentage of olfactory dysfunctions are congenital?
1%.
What are the main causes of acquired olfactory dysfunction?
Chronic rhino-sinusitis, Viral infections, Traumatic brain injuries (e.g., concussion), Neurodegenerative diseases (e.g., Parkinson’s, Alzheimer’s).
What does quantitative olfactory dysfunction refer to?
A decrease or absence in odor perception.
What is anosmia?
A condition where individuals cannot perceive any odors.
What is the prevalence of anosmia?
Affects up to 5% of the population.
What is hyposmia?
A condition where individuals perceive odors only at higher concentrations.
What is the prevalence of hyposmia?
Affects about 15% of the population.
What does qualitative olfactory dysfunction refer to?
When odors are perceived differently or are perceived in the absence of a stimulus.
What is parosmia?
A condition in which odor qualities are distorted (e.g., vanilla smells like burnt rubber).
What is phantosmia?
A condition in which odors are perceived without an actual odor source, typically unpleasant.
Is parosmia common among individuals with hyposmia?
Yes, it often co-occurs with hyposmia.
Is phantosmia common?
No, it is relatively rare.
What is a key difference between chemical and physical senses?
In chemical senses (smell, taste), stimuli enter the body and interact with receptors. In physical senses (vision, hearing), stimuli interact from a distance.
Where are olfactory receptor cells located?
In the olfactory epithelium in the upper nasal cavity.
Are most smells the result of a single molecule?
No, most are mixtures of many odorant molecules.
What are the two pathways by which odorants can enter the nasal cavity?
Orthonasal olfaction – through the nostrils (external source), Retronasal olfaction – from the mouth during eating/drinking.
What type of olfaction is most important for flavor perception?
Retronasal olfaction.
What is unique about olfactory receptor neuron expression?
Each neuron expresses only one type of receptor.
Where do axons of neurons with the same receptor converge?
In the same glomerulus in the olfactory bulb.
What brain system is involved in central olfactory processing?
The limbic system (emotion, memory, reward).
What taste quality is associated with the warning function?
Bitter taste, which is often linked to potentially toxic substances.
Why are humans particularly sensitive to bitter tastes?
Because bitterness helps us detect toxins, often at nanogram or picogram concentrations.
Who are supertasters?
Individuals who are especially sensitive to bitter compounds and usually dislike foods like bitter chocolate, IPA beer, coffee, or licorice.
What taste qualities signal nutritional content?
Sweet (associated with carbohydrates), Umami (associated with proteins).
What taste qualities help regulate electrolyte balance?
Salty (e.g., sodium intake), Sour (linked to pH and acids).
Why might people crave salty foods like poutine after sweating?
To restore electrolyte balance lost through sweat.
What is gustation?
The sense of taste, based on direct contact between tastants and taste receptor cells.
How does taste differ from smell in terms of stimulus delivery?
Taste: Tastants must be dissolved in saliva, Smell: Odorants must be volatile to reach olfactory receptors.
Why is saliva important for taste perception?
Tastants need to be dissolved in saliva to interact with taste receptors.
What might reduce taste sensitivity?
Radiotherapy, Medication, Nervousness (all can impair saliva production).
How many basic taste qualities does gustation detect?
Five: Sweet, Sour, Salty, Bitter, Umami.
How does taste differ from smell in terms of stimulus delivery?
Taste: Tastants must be dissolved in saliva.
Smell: Odorants must be volatile to reach olfactory receptors.
What causes sour taste?
Acids, due to the presence of free protons (H⁺ ions) – lower pH = more sour.
What causes salty taste?
Salts, especially sodium chloride (NaCl).
What is the most prominent umami tastant?
Monosodium glutamate (MSG), a salt of glutamic acid.
In what types of foods is umami commonly found?
Asian cuisine (e.g., soy sauce, fish sauce), Protein-rich foods like mushrooms, bacon, ham, cheeses.
What types of molecules evoke sweet taste?
Carbohydrates like glucose, fructose, and sucrose, which are plant-derived and caloric.
Why do we need to add several grams of sugar to taste sweetness?
Because humans are relatively insensitive to sweet-tasting carbohydrates.
What are some examples of artificial sweeteners?
Aspartame, saccharin, and stevia — they evoke sweetness without providing calories.
What types of molecules evoke bitter taste?
Alkaloids, chemical compounds typically produced by plants.
Are we more sensitive to bitter or sweet tastants? Why?
We are more sensitive to bitter tastants because many alkaloids have pharmacological or toxic effects.
Why do cats not like chocolate?
Cats lack sweet receptors, so chocolate only tastes bitter to them.
Why is chocolate dangerous for dogs?
It contains theobromine, a compound toxic to dogs, even though they can taste its sweetness.
What are papillae on the tongue?
They are bumps on the tongue’s surface that differ in shape, size, and function.
Which type of papillae is not involved in taste?
Filiform papillae – they are the most numerous, cover most of the tongue, and are involved in somatosensation.
What are the three types of papillae involved in gustation?
Fungiform, foliate, and circumvallate papillae.
Where are fungiform papillae located and what is their shape?
They look like mushrooms, appear reddish, and are scattered on the tongue, but most dense at the tip and sides.
What do foliate papillae look like and where are they found?
They resemble short vertical folds and are located on the posterior sides of the tongue.
What is the shape and location of circumvallate papillae?
They are large, have a truncated cone shape, and are surrounded by a circular depression at the very back of the tongue.
Where are taste buds located?
In the epithelium of the papillae on the tongue.
What is the shape of a taste bud under the microscope?
An onion-like shape.
What is the function of the taste pore at the tip of the taste bud?
It allows saliva and tastants to enter the taste bud and reach the taste receptor cells.
Where are gustatory receptors located on the taste receptor cells?
In the hair-like filaments (microvilli) at the top of the cells.
How is the signal from taste sent to the brain?
Through axons emerging from the bottom section of taste receptor cells.
For which taste qualities is the transduction mechanism understood?
Sweet, bitter, and umami.
What type of receptors are involved in sweet, bitter, and umami taste?
G-protein-coupled receptors (GPCRs).
What does binding to GPCRs trigger in the receptor cell?
An intracellular cascade that leads to depolarization of the cell.
For which taste qualities is the mechanism still uncertain?
Sour and salty.
What is the current hypothesis for sour and salty taste transduction?
That electrolytes may directly interact with the cell membrane, or that specific receptors may be involved.
True or False: Certain tastes can only be perceived in specific regions of the tongue.
False. All five taste qualities can be perceived across the entire tongue, though sensitivity may vary by region.
Which cranial nerve conveys taste from the anterior two-thirds of the tongue?
The chorda tympani, a branch of the facial nerve (Cranial Nerve VII).
Where do the taste fibers from the chorda tympani terminate in the brainstem?
In the solitary nucleus.
What condition can lead to loss of taste in the anterior third of the tongue and why?
Chronic middle ear inflammation, because the chorda tympani passes through the middle ear.
Which cranial nerve conveys taste from the posterior third of the tongue and parts of the palate?
The glossopharyngeal nerve (Cranial Nerve IX).
Which cranial nerve conveys taste from the larynx?
The vagus nerve (Cranial Nerve X).
What is the first central relay station for all taste fibers from the cranial nerves?
The solitary nucleus in the medulla (also called the gustatory nucleus of the solitary tract complex).
After the solitary nucleus, where does taste information travel?
To the thalamus.
Is there a thalamic relay for taste information?
Yes, unlike olfaction, taste information must pass through the thalamus.
Where is the primary gustatory cortex located?
In the anterior insular cortex and the frontal operculum.
What motor region is near the primary gustatory cortex?
The region of the motor cortex that controls tongue and larynx movement (lower part of the precentral gyrus).
What somatosensory region is near the gustatory cortex?
The region of the somatosensory cortex that processes touch from the tongue and larynx (lower part of the postcentral gyrus).
Which structure is considered the ‘flavor cortex’?
The orbitofrontal cortex, because it integrates gustatory and olfactory information.
What is the relationship between the primary gustatory cortex and the orbitofrontal cortex?
The primary gustatory cortex sends strong projections to the orbitofrontal cortex, allowing for flavor integration.
What happens when congruent taste and smell stimuli are combined?
They enhance each other. For example, strawberries + sugar increases both perceived sweetness and strawberry flavor.
What happens when incongruent taste and smell stimuli are combined?
They tend to diminish each other’s intensity.
Give an example of a congruent flavor combination.
Strawberries and sugar or bacon and salt.
Give an example of an incongruent flavor combination.
Strawberries and salt — this does not enhance flavor perception.
What is dysgeusia?
Dysgeusia refers to dysfunction of the sense of taste. It includes both quantitative and qualitative disturbances.
What are the types of quantitative gustatory dysfunctions?
Ageusia (complete lack of taste perception) and hypogeusia (reduced taste perception).
Why are ageusia and hypogeusia relatively rare?
Because 6 different cranial nerves (VII, IX, X, bilaterally) are involved in gustatory processing.
What is the ‘release of inhibition’ phenomenon in taste dysfunction?
If one gustatory nerve is impaired, other sectors of the tongue become more sensitive.
What is parageusia?
A qualitative taste dysfunction where tastes are altered, often described as bitter or metallic.
What are common causes of parageusia?
Medications, radiation therapy, and infections like yeast infection of the oral mucosa.
Why are most subjective taste dysfunctions actually olfactory problems?
Because smell contributes significantly to flavor, and anosmia or parosmia are more common than true taste loss.
Where are gustatory receptor cells located?
In taste buds, mainly on the tongue, but also on the palate and in the larynx.
What are the five basic taste qualities?
Sweet, sour, bitter, salty, and umami.
What is umami?
A taste quality associated with glutamate and protein-rich foods; translated from Japanese as ‘savory’.
Which cranial nerves convey taste information to the brainstem?
Facial (VII via chorda tympani), glossopharyngeal (IX), and vagus (X) nerves.
Where do all gustatory nerve fibers converge in the brainstem?
In the solitary nucleus.
Where is the primary gustatory cortex located?
In the anterior insula and the frontal operculum.
What is the role of the orbitofrontal cortex in taste?
It integrates gustatory and olfactory information and is considered the ‘flavor cortex’.
What is the relationship between congruent/incongruent stimuli in taste?
Congruent stimuli enhance each other (e.g., sugar with strawberries), while incongruent stimuli suppress perception.
