Chapter 13 (Taste)

Question 1

Tastants

Answer 1

molecules that taste receptors “recognize” and respond to by producing neural signals that the brain represents as perceptions of different tastes

• Dissolve in saliva and activate taste receptor cells within taste buds,
• Different detection thresholds

Question 2

Basic tastes

Answer 2

five well-established taste categories- sweet, salty, umami, sour and bitter
*Associated with tastants that fill particular nutritive needs

Question 3

Umami

Answer 3

basic taste evoked by tastants such as MSG and certain amino acids found in meats; it generally signals the presence of protein in food

• Recent addition to basic taste
• Glutamate receptors in the gut may serve the protein signaling function

Question 4

Flavor

Answer 4

total sensory experience evoked by ingesting something; it includes the perception of the basic tastes, the perception of other attributes of tastants such as pleasantness and intensity, and other sensory properties, the most important of which is smell

• Comes both from odorants released by the food before it is placed in the mouth (nasal cavity via the nostrils)
• From the odorants released while the food is in the mouth and being chewed and swallowed (nasal cavity via the retronasal pathway)

Question 5

Taste buds

Answer 5

structures that contain taste receptor cells, within papillae in the mouth

• 3,000-12,000 taste buds on average
• A third of them on soft palate, epiglottis, and upper esophagus
• Two-thirds on the tongue, within papillae

Question 6

Papillae

Answer 6

tiny structures on surfaces in the mouth, mainly on the tongue; three different types of papillae contain taste buds

Question 7

Fungiform papillae

Answer 7

tiny mushroom-shaped structures located along the edges and top of the front two-thirds of the tongue, each fungiform papilla contains 3-5 taste buds on its upper surface

Question 8

Foliate papillae

Answer 8

ridgelike folds of tissue located on the sides of the tongue near the back; a few hundred taste buds are tucked into each fold

Question 9

Circumvallate papillae

Answer 9

mushroom-shaped structures (much larger than fungiform papillae) situated in a row at the back of the tongue; each circumvallate papilla contains 200-700 taste buds around its sides

Question 10

Filiform papillae

Answer 10

don’t contain taste buds, cover much of the tongue’s surface; contain somatosensory receptors thought to provide information about the texture of food
*Most common

Question 11

Taste receptor cells (TRCs)

Answer 11

elongated neurons with cilia at their outer ends and without axons, packed within taste buds, that transduce tastants into neural signals

• Each TRC lives for only a week or so and is then replaced
• New TRCs develop from basal cells in the taste buds
• The cilia of the TRCs project into a taste pore (opening onto the surface of the tongue) at the top of the taste bud, where the cilia come into contact with tastant molecules dissolved in saliva

Question 12

Receptor cells

Answer 12

type of taste receptor cells containing receptors that initiate transduction of sweet, umami, and bitter tastants

• Each receptor cell contains only a single category of receptors on its cilia
• Do not have synapses with cranial nerve fibers

Question 13

Presynaptic cells

Answer 13

a type of taste receptor cells in which the receptors take the form of ion channels where transduction of salty and sour tastants is initiate
* Inner ends of presynaptic cells release neurotransmitters into synapses with cranial nerve fibers that send taste signals to the brain

Question 14

Cell-to-cell signaling

Answer 14

signals from receptor cells to presynaptic cells, causing the presynaptic cells to release neurotransmitters in a way that carries information about sweet, umami, and bitter tastes.

Question 15

Labeled-line model

Answer 15

each cranial nerve fiber carries signals with information about just one of the five taste qualities, and that the cortical neurons on the receiving end of these signals also respond only to information about a single type of tastant.
* There is a single “labeled line” from the specialized TRCs in taste buds to correspondingly specialized cranial nerve fibers to correspondingly specialized cortical neurons.

Question 16

Across-fiber pattern model

Answer 16

cranial nerve fibers can carry signals from multiple taste receptor types, and that the cortical neurons receiving these signals are broadly tuned to respond to signals carrying information about multiple types of tastants.
*cranial nerve fibers carry information about differences in taste quality based on the relative activity of a few different types of receptors (TIR1-TIR3, TIR2-TIR3, T2R2, and 3 different ion channels)

Question 17

Facial nerve (Cranial nerve VII)

Answer 17

innervates the front two-thirds of the tongue and the soft palate

Question 18

Glossopharyngeal nerve (Cranial nerve IX)

Answer 18

innervates the back one-third of the tongue

Question 19

Vagus nerve (Cranial nerve X)

Answer 19

innervates the epiglottis and the upper esophagus

Question 20

Primary taste cortex

Answer 20

first cortical areas to receive taste signals, consisting of the anterior insular cortex and the frontal operculum
*taste qualities; identify tastants

Question 21

Orbitofrontal cortex (OFC)

Answer 21

Respond strongly- indicating high reward value- only when the animal is hungry.

• Motivate organisms to eat when they’re hungry
• Pleasantness of eating flavorful foods
• Receives signals not only from the primary taste cortex but also from many other sensory modalities
• Flavor, reward value

Question 22

eNose

Answer 22

electronic nose; capable of detecting and identifying odorants, localizing their source, and even tracking odor plumes

• Sampling the chemical composition of the air in environments
• Helping diagnose diseases that often produce characteristic odors in concentrations too low for the human nose to detect and identify
• Detecting drugs or explosives
• Monitoring foods for freshness and possible contamination

Question 23

Orthonasal and retronasal

Answer 23

From the front of the nose and from the back of the nose

• odors have different significance if they come from the mouth or from the outside world.
• Outside the world or inside your mouth

Question 24

Super tasters

Answer 24

Experience heightened taste sensations to a broad range of tastes

• Higher density of fungiform papillae on the tongue and presumably, higher density of taste receptors
• 35% women; 15% men
• Intense sensations of oral burn, oral touch, retronasal olfaction, intense flavor (by trigeminal somatosensory nerve)