Perception 212- Chapter 4: Taste & Smell

What taste quality measurement technique is commonly used in beer production?

Rating system. Ratings of taste impressions are plotted on a scale of 0-10, resulting in taste maps used to make comparisons.

When similar compounds elicit more intense sensations of that quality, they are of a (homogenous/heterogenous) mixture.

Homogenous mixture. eg. MSG in salty foods.

What are 3 abnormalities of olfactory function that can occur in humans?

Hyposmia (caused by infection or injury), anosmia (a genetic condition), and specific anosmia.

What is the subject required to do in an 8-cup test?

Identify which 4 of 8 cups contains the stimulus.

Instead of labeled-line coding, how are signals coded?

Individual receptor cells are capable of responding to several taste stimu. through various transduction mechanisms.

How does the human chemosensory function differ from that of other animals?

- Humans do not have a functional vomeronasal organ (a separate organ in the nasal cavity of certain animals, used to detect pheromones). - Sensitivity of smell is way reduced (dogs up to 10,000x more sensitive)

What protein in the olfactory epithelium helps hydrophobic odorants across the mucous layer of the olf. epithelium?

Odorant binding proteins (OBP), which attaches to different kinds of hydrophobic odorants.

The features of an odourant molecule nec. to trigger a neural response are known collectively as the...?

Odotope.

What is used to deliver brief, controlled pulses of air with fixed concentrations of an odorant in olfactory sensitivity experiments?

Olfactometers.

There are 3 types of cells of which the olf. epithelium is composed of. Identify them and briefly explain their function(s).

Olfactory sensory neurons (bipolar neurons that join together to form a nerve bundle which projects to olfactory bulb, and have a lifespan of 30-60 days). Basal Cell: provide source for replacement of dying sensory neurons (<5% cell.pop.) Supporting cell: produces mucous, regulates mucus ionic content.

The Henning Smell Prism is based on which 6 categories?

Putrid, flowery, fruity, spicy, resinous and burnt (but the prism is too simple).

Sourness reduces the percieved taste of...? Why?

Saltiness. Because the hydrogen atoms released from acidic substances compete with sodium channels in microvilli.

What is the detection threshold for the 3-drop test? In general, thresholds are high/low for this technique?

When the subject detects correct drop 3 times in a row. Thresholds are generally high due to small volume.

What technique are the 3-drop test and 8-cup test examples of?

Whole-mouth technique.

What substance is known to trigger umami receptors?

monosodium glutamate (MSG).

From where does the primary olfactory cortex receive direct axonal projections?

the olfactory bulb.

What is the Proust phenomenon?

When certain odors seem to trigger emotional states/memories

What is cross-adaptation?

When sensitivity to one odorant is reduced by exposure to a different one.

What do the terms 'non-tasters, tasters and supertasters' refer to?

25% of people are non-tasters (cannot taste butter substances PTC/PROP.) 75% are able to; tasters. 1/4 of tasters are supertasters (highly sensitive).

How many receptor cells might a single tastebud have?

50-150 receptor cells.

The relationship between DT of taste and temp. shows a what-shaped function?

A U-shaped function.

What is a 'characteristic smell signature'?

A person's distinctive set of odors.

What effect does exaltolide have on women?

A sexually stimulating effect, especially when in going through the menstrual cycle and estrogen affects the mucous layer.

At the functional level, is signal processing consistent with labeled-line method?

Nope. Different odorants produce a characteristic odor image.

How many taste buds do we have, and where are they located?

About 4,600 taste buds. They are found in the roof of the mouth, back of the throat, and tongue.

As you are exposed to an odor for a period of time, your DT for that odor temporarily increases. What is this phenomenon called?

Adaptation.

What are the 3 taste dysfunctions that can occur, and what are the symptoms?

Ageusia (total loss of taste) Hypogeusia (reduced taste sensitivity) Dysgeusia (taste distortions)

Give 2 examples of the importance of smell in humans.

Babies detect odor of mother's breasts and are repulsed by strangers. Mensrual synchrony among women in dorms. This is an example of odors affecting behavior.

Why does adaptation to the flavoring of food not occur?

Because the food in suspected to continual movement on the tongue.

How come both the labelled-line and cross-fiber theories are accepted in olfaction and gustation?

Because there appears to be a precise anatomical relationship between receptor neurons and invidual glomeruli. However, odorant receptors are capable of binding different odorants, and so appears to be multidimensional.

What is the temperature range for highest sensitivity (lowest DT)?

Betwwen body temp. (37 degrees) and room temp. (22 degrees). NOT body temperature.

Recognition thresholds are susceptible to criterion effects. What are criterion effects?

Biases towards certain odorants

How does DT vary for the different taste primaries?

Bitter has lowest DT, then sour, salty and sweet has the highest DT. Exceptions: saccharin has low DT, and urea has high.

Which tastants, when its G-protein is triggered, releases calcium ions which trigger NT release?

Bitter tastants.

True or False: hunger/satiety affects firing of neurons in the PGC.

False. The integration of taste perception modulation by motivational factors occurs in the SGC in the orbitofrontal cortex.

The primary gustatory cortex is located in..?

The insula.

What do VNO neurons not have that olfactory neurons do?

Cilia.

What kind of coding does the following describe: Different taste qualities are distinguished by a pattern of discharges across a large population of fibers.

Cross-fiber coding. (Pfaffman: a certain taste quality is encoded by pattern of firing in a large set of nerve fibers)

What is the bitterest substance known?

Denatonium benzoate.

What is electrogustometry often used for, and what is a disadvantage and advantage of it?

Electrogustometry is often used to obtain taste thresholds and assess taste dysfunction. Disadvantage: limited to salt/sour (ionic channels) Advantage: discrete in terms of space and time, unlike chemicals

True or False: The tongue is divided into discrete regions, each of which processed different taste qualities.

False. All 4 taste qualities are processed by tastebuds throughout the tongue.

True or False: each olf. sensory neuron expresses more than one type of receptor.

False. Each olf. sensory neuron expresses exactly one type of receptor, and produces a signal only when that receptor is stimulated.

True or false: hot/spiciness is a gustatory quality.

False. It is a result of chemical irritation to thermal/nociceptive fibers.

True or false: Pheromonal chemicals are small, volatile chemicals.

False. Pheromonal chemicals are large and generally non-volatile.

True of false: there is one type of tastebud receptor cell.

False. There are 2: light and dark receptor cells that taper toward the pore of the tastebud to interact with microvilli there. Tastants are sense by microvilli and the receptro cells are triggered to release NT.

True or false: cranial nerves only transmit taste signals.

False. These cranial nerves also carry non-taste signals like touch and pain.

List the 3 different kinds of papillae and their general locations.

Fungiform (tip), vallate (contains almost half of taste buds, V-shaped formation at back of tongue), and foliate (back and sides, create deep ridges).

In the olf. bulb, what structures do incoming axons converge onto?

Glomeruli. One OSN projects to one glomerulus, but each glomerulus receives axons from several OSN.

What kind of fiber does receptor cells in the tastebuds synapse with?

Gustatory nerve fiber.

When two qualities mutually suppress each other, and mask each other, they are known as (homogenous/heterogenous) mixtures, eg. sweet and sour lemonade.

Heterogenous.

With the concept of masking in mind, how does the presence of sucrose/citric acid in salt solution affect the threshold for salt?

It raises the threshold for salt x3

What method is used to measure the suprathreshold intensity in olfaction?

Magnitude estimation tasks, where the subject

Receptors in the OSN are metabotropic/ionotropic?

Metabotropic. They have secondary messengers (G-protein->cAMP->opening of ionic channels).

Which Fechnarian methods are used to obtain detection and recognition thresholds in olfaction?

Method of constant stimuli and method of limits, as well as newer methods.

What is a more suitable way to represent taste quality?

Multi-dimensional scaling, where numeric results for similarity of tastes are placed on a geometric space. Several compounds lie outside of the Henning pyramid.

Do compounds representing the four classical taste qualities cross-adapt each other?

No, because there is a separate and independent transduction mechanism for each quality.

Does smoking affect olfactory thresholds?

No.

Which tastants bind to receptors coupled with G-proteins, which then produces cyclic AMP (which in turn act directly on ionic channels to produce depolarization)?

Sweet tastants.

Although taste quality sensation in the tongue is not divided into discrete regions, explain the general chemotopic organization for SENSITIVITY to certain taste primaries.

Sweet/salty: higher sensitivity at tip (facial nerve) Sour/bitter: higher sensitivity near back of tongue (glosso.nerve)

True or False: Stimuli that produce similar tastes have similar patterns of firing.

TRUE :)

True or False: The Weber exponent for for primary taste qualities is <1 (a negatively accelerating function).

TRUE.

What was the assumption behind Henning's 3-sided pyramid?

That all complex tastes arise from a mixture of the 4 primaries.

Primary taste qualities have their own signal transduction mechanisms. What are they and how do they correspond to taste qualities?

The 2 signal transduction mechanisms are ionic channels (code of sour/salty) and receptor-mediated channels (code for sweet/bitter).

In what way is the cross-fiber theory of gustatory processing difficult to reconcile with that of taste primaries?

The coding of separate taste primaries is not maintained in the transmission of neural signals to the brain areas.

What is labeled-line coding in terms of gustation? Is it really the case for gustation?

The concept that each nerve fiber is responsible for transmitting information that is highly specific and restricted to a particular taste quality. This is not true for gustation.

The gustatory nerve fiber carries APs along which 3 cranial nerves?

The facial nerve, the glossopharyngeal nerve, and the vagus nerve.

What are taste hedonics?

The hedonic aspects of taste perception concern the evaluation of foods with regard to its positive or negative appreciation.

What is the first subcortical relay site for gustatory signals, and where is it located?

The nucleus of the solitary tract (NST), which is a collection of neurons located in the brain stem. (also features a general chemotopic organization)

Where does discrimination of odors and smell-taste integration occur in flavor perception?

The orbitofrontal cortex.

Odorants pass through which 2 routes of complex conduits of nasal channels?

The orthonasal route (odorants reach olf. epithelium through nasal passages), and the retronasal route (located in the back of the throat).

Which part of the cortex is considered the main olfactory processor?

The piriform cortex (a 3-layered structure with an extensive network of circuits).

Which part of the cortex is considered the main olfactory processor?

The piriform cortex.

Where do the fibers from the VPMN project to?

The primary gustatory cortex, the first site in the CC where taste signals are processed.

In gustation, the orbitofrontal frontal cortex is also known as?

The secondary gustatory cortex.

What is the second cortical relay site?

The ventral posterior medial nucleus (VPMN). The neurons here are small and densely packed, and responds mostly to sweet/salty.

Noxious chemicals are detected by systems separate from the olfactory system. What kind of reception is involved in the 'common chemical sense'?

Trigeminal chemoreception, where trigeminal nerves give rise to free nerve endings with detect noxious chemicals.

True or False: A single nerve fiber can receive signals from more than one tastebud, and tastebuds can send signals through more than one gustatory fiber.

True.

True or false: each glomerulus serves an independent coding unit.

True.

True or false: taste is a categorical sensory dimension.

True. It is a metathetic sensation.

True or false: There is a direct neural link between the olfactory bulb and the limbic system.

True. There is a direct link between the olf. bulb and the amygdala and hippocampus (trigger/store emotional experiences and memory traces).

Glutamate (also found in proteins) binds specifically with which taste receptors?

Umami receptors.

How do receptor cells in the taste buds act as neurons?

When binded with a tastant molecule, a membrane potential change is produced within the receptor cell, which triggers NT release.