Chemical Senses Flashcards
What is flavour?
A combination of smell and taste
Can include texture and other sensory aspects
What is difficult to identify without olfaction?
Foods
How did our gustation adapt?
To test whether food was edible, spoiled, or poisonous
What do salty foods maintain?
Electrolyte balance
What do sour foods do?
Detect vitamins and acids that cold burn tissue
What does sweet food ensure?
Energy reserves and fuel for neurons
What is the purpose of bitter tastes?
To avoid toxins/poisons
What are the qualities of salty stimuli?
in-/organic salts
Cation is the most important
What are the qualities of sour stimuli?
in/organic acids that release H+ ion in solution
What are the qualities of sweet stimuli?
Complex organic molecules: sugar, aspartame
What are the qualities of bitter stimuli?
Varied
Alkaloids
Some nitrogen-containing molecules
What are the qualities of umami stimuli?
Savory
Salts of glutamic acid
Where are salts of glutamic acid found?
Protein-rich foods
Was isolated from seaweed
What is MSG?
Glutamic acid + Na+
There are G protein-coupled receptors for MSG
What are the bumps on the tongue called?
Papillae
Where are taste buds found?
The fungiform = on tip and sides
Foliate = folds along sides of tongue
Circumvallate = flat mounds surrounded by a trench on the back of the tongue
Soft palate
What projects out of the taste pore?
Microvilli.
How does the transduction of taste work?
Sodium penetrates membrane of the receptor = depolarization
Sour substances contain H+ which blocks ion channels
Other substances form bonds with molecules in the membrane causing chemical changes within the cell
What is label-line sensory coding?
Different taste stimuli activate specific fibers
The firing rate represents the intensity
Activity in a few fibre types is all that is needed to code stimuli
What is the problem with label-line sensory coding?
Many substances elicit more than one taste
What is cross-fibre patterning?
There are no specialized receptors for each taste
Taste quality signaled by the pattern of activity in many fibers
Each fiber responds to a variety of substances, but is tuned to respond best to one type of taste
What nerve is made up from nerve fibers from the front and sides of the tongue?
The chorda tympani nerve
What nerve is made up from fibers from the back of the tongue?
The glossopharyngeal nerve
What nerve is made up from fibers from the mouth and throat?
The vagus nerve
What nerve is made up of fibers from the soft palate?
The superficial petrosal nerve
Where do all of the nerves connect to?
The nucleus of the solitary tract in the medulla
What are the pathways in the medulla?
Thalamus => gustatory cortexes in the frontal lobe
Frontal operculum cortex and anterial insula (conscious taste perception) -> orbitofrontal cortex (emotion and reward)
What role does the hypothalamus and the amygdala play in taste?
Aversions, cravings, affect component of taste
What factors affect the taste threshold?
Location = tastes are NOT localized on the tongue
Temperature of substances = greatest sensitivity around 22-40°C
Individual differences (like PTC gene)
What is adaptation-produced potentiation?
Adaptation to one taste increases sensitivity to another
What is cross-adapatation?
Adaptation to one compound reduces sensitivity to another compound
Occurs for salty and sour (common mechanisms?)
Not for sweet and bitter (multiple coding mechanisms?)
What is chemesthesis?
Sensations arising when chemical compounds in foods activate receptor mechanisms for pain, touch or thermal perception
What are some characteristics of capsaicin?
Found in white membrane inside of chili peppers
Soluble in alcohol and vegetable oil
Measured in scoville heat units
How does capsaicin work?
Partly comprised of a vanillin-shaped molecule so will bring to TRPV1 (vanilloid receptor 1) which is a polymodal nociceptor of some C-fibers which is why spice can be painfully hot
Causes an influx of Ca2+ and Na+ into cells, triggers heat signal and inflammation
What is menthol?
Alcohol extracted from peppermint, potent counterirritant
Produces cool sensation, acts on thermoreceptors
How does menthol work?
Acts of TRPM8 protein which is a cold receptor
Menthol inhibits efflux of Ca2+ from cold receptor which causes increased firing
What are odourants?
Molecules of volatile substances
How do perfumers categorize smells?
Top notes, middle notes, base nots
What were Artistotle’s 4 basic categories of odourants?
Pungent, succulent, acid, astringent
What is the odour prism?
Any odour is a combination of qualities on the prism
We need more than 6 categories though
What is a stereochemical theory?
The classification of odours based on the shape of molecules
Certain shaped molecules fit into matching receptor sites
What are the pros for stereochemical theory?
Evidence for categories from different kinds of anosmia = inability to perceive a certain odour
2hat are the cons of stereochemical theory
Contrary evidence
Very similar molecules can have different odours and vice versa
What is in the roof of the nasal cavity?
The olfactory mucosa which contains mucous and olfactory epithelium
What can olfactory stimuli be picked up by?
Olfactory binding proteins in the mucous layer
What do molecules bind to in olfaction?
Olfactory receptors or cilia of olfactory receptors
What are the neural pathways in olfaction?
Olfactory nerve goes to olfactory bulb
One pathway goes to primary olfactory (piriform) cortex in temporal lobe and then to the secondary (orbitofrontal) olfactory cortex
Another goes to the limbic system
Where does olfaction NOT travel through?
The thalamus
What are glomeruli?
Clusters formed from ORN axons/dendrites of the olfactory bulb neurons
What factors affect the threshold for olfaction?
Age
Smoking
Menstrual cycle
Individual differences can be as great as 20x
What are the differences between olfaction in humans and in dogs?
Dogs can detect substances in concentrations 300-10000x lower than humans BUT human olfactory receptors are triggered by one molecule
Dogs = 1 billion ORNs + 100-150 cilia
Humans = 10 million ORNs + 6-8 cilia
What is the effect of COVID on olfaction?
The virus attacks sustentacular cells that support ORNs, causing shedding of the cells of the olfactory epithelium
What is aromachology?
The study of the influence of smells on behaviour, mood and emotion
How does linalool affect stress response in rats?
Caused white blood cell levels to return to normal and changed expression in 115 genes
Odorants can reverse the effects of stress on the immune system
How does inhaling peppermint affect athletes?
Increases performance on running speed, grip strength, number of push ups
Not basketball free throws though
How does cinnamon gum affect athletes?
Increases performance on attention-based, memory, and visual-motor tasks
What is the issue with these specific athletic performance studies?
No control group
How does inhaling neutral sweet smells when hungry affect weight loss?
Causes a mean weight loss of 30 lbs in obese patients
What is the Proust effect?
Certain odourants trigger associated autobiographical memories
What did Schab find about memory and smell?
Participants who were presented a smell while being presented words could recall them better later when the smell was presented again
What are pheromones?
Chemicals secreted by animals transmit information to others of the same species
What are releaser pheromones?
Trigger immediate behavioural response in another animal
What are primer pheromones?
Start long-lasting physiological effects in another animal
What is the Bruce effect?
Female mouse that has just mated will not become pregnant if it smells a strange male mouse
What are pheromones detected by?
The vomeronasal organ in the base of the nasal cavity
What is musk?
Secreted from the abdominal gland of a male musk deer
What is musk similar to?
Human testosterone
What is alpha androstenol?
Secreted in human sweat, mostly by women
A sex attractant for pigs
What might sexual arousal due to smells be due to?
Conditioned response to sexual partner/favourite food
Nostalgic recall
Relaxation of odour
Neurophysiological response
