3. Taste

Question 1

What is Taste?

Background
• All life forms need energy to survive. In order to obtain the essential energy and resources necessary for life, humans must consume food.
• If there was no indulgent satisfaction from our eating habits, food consumption would be a tedious task that required a lot of effort.
• The ____ pleasure of eating compensates for this hard work. This pleasure never subsides, and is experienced whenever we eat. Unlike other stimulants, eating food is an easy way to receive instant, constant and satisfying gratification.

Answer 1

emotional

Question 2

What is Taste?
Background
• If we define taste only as a gustatory sense through the biochemistry in our mouth, there are five basic taste elements: ____, saltiness, ____, bitterness, and ____ (savory).
• However, can we describe all the characteristic tastes of thousands of cuisines with the combinations of only these five basic tastes? – Of course not.
• The characteristic taste of a food is a result of a combination of these five elements combined with many other aspects of the food: Taste is complex.

Answer 2

sweetness
sourness
umami

Question 3

What is Taste?

Background
• The unique tastes (flavors) of food are in part created by combinations of thousands of volatile odorants transferred to the nasal cavity when we eat food - consequently a food may ‘taste different’ in patients suffering from nasal congestion.
• ____ nerve stimulation (texture, temperature, etc.) also contributes to the overall flavors of food.

Answer 3

trigeminal

Question 4

Taste
• The conclusions of this taste map were ____, being based on experiments with a small number of research subjects.
• Recent studies have verified that humans can identify all taste chemicals from all ____ of the tongue.
• The taste map episode is a great example of how difficult it is to eradicate stereotypes, even in scientific fields.

Answer 4

premature

regions

Question 5

• He concluded that there is a fifth basic taste: Umami and he later found the mysterious molecule was ____.

Answer 5

glutamic acid

Question 6

Taste
• Glutamic acid is a common amino acid that is a component of proteins.
• When glutamic acid is polymerized to a peptide along with other common amino acids, it loses its taste due to the ____ molecular weight.
• When the tasteless protein is ____ to release free amino acids through the process of fermentation or cooking, we can taste the glutamic acid.

Answer 6

increased

hydrolyzed

Question 7

Taste
• In addition to glutamic acid, other chemical compounds have been identified that exhibit umami.
• ____, a nucleotide seasoning component, was discovered from katsuobushi (dried skipjack tuna flake) in 1913, and guanylic acid was isolated from shiitake mushroom in 1957.
• Since 1985 umami has been accepted as the fifth basic taste.
• Scientists found the umami receptor in the taste buds of mice in 1997 and in the human tongue in 2000.

Answer 7

inosinic acid

Question 8

Why do we Taste?

Sweet
• Living organisms require sugars for the storage of chemical energy. Biochemical energy for cellular activities is obtained from ____ (adenosine triphosphate), which is produced by hydrolysis of ____ (carbohydrates).
• The brain responds with pleasure when we find sugars with our sweet taste receptors. Sensing sweetness indicates that the food will help with our demand for energy.
• There are ____-carbohydrate molecules that trigger the sweet receptor, and these have led to the development of artificial sweeteners.

Answer 8

ATP
sugars
non

Question 9

Why do we Taste?

Sour
• For newborn babies, sour foods are naturally ____. Sourness can be enjoyed after learning, but they are not naturally enjoyable as sweetness or umami are.
• Sensing the presence of acid is used to alert us to the ____ condition of the food.
• Sour taste can signal under-ripe fruit, rotten meat and other spoiled foods which can be ____ to the body.

Answer 9

rejected
unhealthy
dangerous

Question 10

Why do we Taste?

Salt
• The detection of salt is important to many organisms as it serves a critical role in ion and ____ homeostasis in the body.
• Because of this, salt elicits a ____ taste in most humans.

Answer 10

water

pleasant

Question 11

Why do we Taste?

Bitter
• The bitter taste is almost universally ____ to humans. This is because many ____ organic molecules which can poison humans taste bitter.

Answer 11

unpleasant

nitrogenous

Question 12

Why do we Taste?

Umami (savory)
• Proteins are essential biochemical substances and humans must ingest proteins in their diet.
• Proteins are ____: This is because any polypeptide with more than ten amino acids is too big to bind with the binding site of the amino acid taste receptors.
• ____ amino acids do possess taste, even at very low levels of concentration.
• The umami taste is generally a ____ and encourages the intake of peptides and protein.

Answer 12

tasteless
free
pleasurable

Question 13

Taste

Background
• Both smell and taste receptors are ____ that are stimulated by molecules in solution in mucus in the nose and saliva in the mouth.
• Because stimuli arrive from an external source, they are also classified as ____.
• The sensations of smell and taste allow individuals to distinguish between estimates of up to 30 million compounds that are present in food, predators, and mates and to convert the information received into appropriate behaviors.

Answer 13

chemoreceptors

exteroceptors

Question 14

Taste

Background
• Taste is critical for identifying substances in foods and beverages, such as sugars and poisonous alkaloids, that promote or disrupt homeostasis.
• In the oral cavity, the taste receptor cells are located within ____, mostly on protuberances called ____.
• Like olfactory receptor cells, taste receptor cells periodically die and become ____.

Answer 14

taste buds
papillae
replaced

Question 15

Taste

Taste buds
• There are approximately 10,000 taste buds in the oral cavity, which are ____ bodies measuring 50–70 μm.
• There are four morphologically distinct types of cells within each taste bud: ____ cells, dark cells, ____ cells, and intermediate cells. The latter three cell types are also referred to as Type ____ taste cells.
• These taste cells are the ____ neurons that respond to taste stimuli or tastants.
• Each taste bud has between 50 and 100 taste cells.

Answer 15

ovoid
basal
light
I, II and III
sensory

Question 16

Taste

Taste buds
• The apical ends of taste cells have microvilli that project into the taste pore, a small opening on the dorsal surface of the tongue where tastes cells are exposed to the oral contents.
• Each taste bud is innervated by about 50 nerve fibers, and each nerve fiber receives input from an average of ____ taste buds.
• The basal cells arise from the ____ cells surrounding the taste bud. They differentiate into new taste cells, and the old cells are continuously replaced with a half-time of ____ days.

Answer 16

five
epithelial
10

Question 17

Taste

Taste buds
• In humans, the taste buds are located in the mucosa of the ____, palate, pharynx, and in the walls of papillae of the tongue.
• The circumvallate papillae are prominent structures arranged in a ____ on the back of the tongue.
• The foliate papillae are on the ____ edge of the tongue.
• The fungiform papillae are rounded structures most numerous near the ____ of the tongue.

Answer 17

epiglottis
V
posterior
tip

Question 18

Taste

Taste buds
• Taste buds on the anterior two-thirds of the tongue are innervated by the ____ branch of the ____ nerve.
• Taste buds on the posterior one-third of the tongue are innervated by the ____ branch of the ____l nerve.
• Taste buds in the pharynx are innervated by the ____ nerve.

Answer 18

chorda tympani
facial
lingual
glossopharyngeal
vagus

Question 19

Taste

Taste buds
• Each fungiform papilla has up to ____ taste buds, mostly located at the ____ of the papilla.

Answer 19

five

top

Question 20

Taste

Taste Buds
• Each circumvallate and foliate papilla contain up to 100 taste buds, mostly located along the ____ of the papillae.

Answer 20

sides

Question 21

Taste

Taste buds
• Keep in mind: ____ papilla do not have taste buds.

Answer 21

filliform

Question 22

Taste

Taste buds
• The von Ebner glands (also known as gustatory glands or serous glands) secrete saliva into the cleft around the ____ and ____ papillae.
• Secretions from these glands may function to ____ the mouth to prepare the taste receptors for a new stimulant.

Answer 22

circumvallate
foliate
cleanse

Question 23

Taste

Taste transduction
• It has become clear that individual taste qualities or even individual taste compounds use ____ transduction mechanisms.
• In general, taste transduction is initiated when soluble chemicals diffuse through the contents of the taste pore and interact with receptors located on the exposed apical microvilli of the taste cells.

Answer 23

several

Question 24

Taste

Taste transduction
• The interaction of the chemical stimulus with the taste cell receptor results in depolarization of the taste cell microvilli.
• Depolarizing potentials of sufficient magnitude result in action potential generation within taste cells, which in turn produce an increase in intracellular ____, either by the release of calcium from ____ stores or by the activation of voltage-gated ____ channels located in the basolateral membrane of taste cells.

Answer 24

calcium
internal
calcium

Question 25

Taste

Taste transduction
• This calcium release results in a release of chemical transmitters at the ____ synapse, which in turn leads to an action potential in the afferent fiber.

Answer 25

afferent

Question 26

Taste

Tastant - sweet
• The sweet taste is ____ caused by any single
class of chemicals.
• Some of the types of chemicals that cause this taste include ____, glycols, alcohols, ____, ketones, amides, esters, some amino acids, some small proteins, sulfonic acids, halogenated acids, and inorganic salts of lead and beryllium.

Answer 26

not
sugars
aldehydes

Question 27

Taste

Tastant - sweet
• The reason why artificial sweeteners are ____ than sucrose is because the forces binding them to the receptors are ____.
• These stronger binding forces last ____ so artificial sweeteners such as saccharine and aspartame score much higher on the sweetness index, even for much smaller amounts.

Answer 27

sweeter
stronger
longer

Question 28

Taste
• At room temperature, the average values for the relative sweetness are: ____ (120), sucrose (100), glucose (64), galactose (50), maltose (43), and ____ (33).
• For artificial sweeteners: ____ (50,000), aspartame (20,000), and ____ (25,000).

Answer 28

fructose
lactose
saccharine
stevioside

Question 29

Taste

Tastant - sweet
• Different kinds of sugar can provide different types of sweetness.
• The sweetness of sucrose lasts a ____ time but it takes some time to bind to the receptors and to initiate the neuro-signal.
• The sweetness of fructose is recognized ____ and at a greater magnitude but the taste also disappears very ____.
• The sweetness of maltose syrup is sensed ____ and faintly but it persists for a ____ time.

Answer 29

long
quickly
fast
slowly
longer

Question 30

Taste

Tastant - sweet
• The binding forces of sugar molecules to the sweet taste receptors of humans vary depending on their structural status.
• At refrigeration temperature, the relative sweetness of ____ is nearly double that of sucrose.
• Therefore, in cold drinks, half the amount of fructose can exhibit the same magnitude of sweetness as that of sucrose, but with less ____. This is why high fructose corn syrup is widely used for cold beverages and sucrose is commonly used in coffee or tea

Answer 30

fructose

calories

Question 31

Taste

Tastant - sour
• The sour taste is caused by ____ (by the hydrogen ion concentration) and the intensity of this taste sensation is approximately proportional to the logarithm of the ____ ion concentration.
• In addition, different types acids result in different sour tastes.
• The tongue detects the sourness of ____ acid and tartaric acid quickly, but that of ____ acid, lactic acid, and fumaric acid more slowly.

Answer 31

acids
hydrogen
citric
malic

Question 32

Taste

Tastant - salt

• The salty taste is elicited by ionized salts, mainly by the ____ ion concentration.
  
  • The quality of the taste varies somewhat from one salt to another because some salts elicit other taste sensations in addition to saltiness. The ____ of the salts are mainly responsible for the salty taste, but the ____ also contribute to a lesser extent.

Answer 32

sodium
cations
anions

Question 33

Taste

Tastant - bitter
• The bitter taste, like the sweet taste, is ____ caused
by any single type of chemical agent.
• Two particular classes of substances are especially likely to cause bitter taste sensations:
(1) ____-chain organic substances that contain ____
(2) ____

Answer 33

not
long
nitrogen
alkaloids

Question 34

Taste

Tastant – Umami (savory) acids.
• The umami taste is produced by ____ acidic amino
• Acidic amino acids, such as glutamic acid and aspartic acid, dissolve easily in ____, and produce the umami taste.
• The glutamic acid molecule is a little longer and has a umami level that is ____ times stronger than aspartic acid.
• Not all amino acids produce the umami taste: Low water soluble amino acids taste ____; low molecular weight or highly water soluble amino acids taste ____.

Answer 34

free
water
three
bitter
sweet

Question 35

Taste

Tastant - umami (savory)
• ____, milk, cheese, yogurt, and every other product derived from cows contain high concentrations of glutamic acid.
• ____ and other seafoods contain high levels of glutamic acid regardless of whether they are ____ or saltwater.
• ____ products such as bean sprouts, tofu, soy sauce, soy paste, and soy milk contain high levels of glutamic acid and high concentrations can also be found in various flour based products such as ____ and noodles.

Answer 35

beef
fish
soybean
breads

Question 36

Taste

Tastant - umami (savory)
• Many cooking methods are designed to release glutamic acid and enhance the umami taste.
• When meats are cooked, glutamic acid is produced from proteins. For example, the concentration of free glutamic acid increases when meat is aged to produce hams.
• ____, a highly water soluble sodium salt of glutamic acid, is often used in asian cooking to enhance umami.

Answer 36

monosodium glutamate (MSG)

Question 37

Taste

Tastant - umami (savory)

• MSG: is it toxic?
  When glutamic acid is purified, it forms ____ that cannot dissolve in water. To make the glutamic acid soluble, ____ ions are added.
  Once it has dissolved in water, it forms the same natural glutamic acid with free sodium salts.
  The FDA recognizes it as safe but due to reported adverse reactions – ____, nausea, weakness – they require that it is listed on the label.

Answer 37

crystals
sodium
headaches

Question 38

Taste

Tastant - umami (savory)
• In addition to glutamic acid, some ____ acids have umami.
• The most common umami tasting nucleic acids are ____ acid and ____ acid.

Answer 38

nucleic
5-inosinic
5-guanylic

Question 39

Taste

Receptors
• The receptors for the five modalities of taste include two major types of receptors: ____-gated channels (ionotropic receptors) and ____- coupled receptors (metabotropic receptors).

• ____ tastes are triggered by activation of ionotropic receptors.
• ____ tastes are triggered by activation of metabotropic receptors.

Answer 39

ligand
g-protein

salt and sour

sweet, bitter, and umami

Question 40

Taste

Receptors
• ____ sensations are mediated through the epithelial sodium channel when Na+ crosses the channel.
• ____ sensations are mediated through ion channels with the movement of H+.
• ____ sensations arise from a small family of three G- protein-coupled receptors termed T1R1, T1R2, and T1R3.
• ____ sensations arise from the G-protein coupled receptor mGluR4.
• ____ is mediated by the T2R receptors, a family of ~30 G-protein-coupled receptors.

Answer 40

salt
sour
sweet
umami
bitter

Question 41

Taste

Taste Pathways
• The sensory nerve fibers from the taste buds on the anterior two-thirds of the tongue travel in the ____ branch of the ____ nerve.
• The sensory nerve fibers from the posterior third of the tongue reach the ____ via the ____ nerve.
• The fibers from areas other than the tongue (eg, pharynx) reach the brain stem via the ____ nerve.

Answer 41

chorda tympani
facial
brainstem
glossopharyngeal
vagus

Question 42

Taste

Taste Pathways
• The taste fibers in these three nerves unite in the ____ in the medulla oblongata.
• From there, axons of second-order neurons ascend in the ____ medial lemniscus and project directly to the ____ of the thalamus.
• Unlike other ascending sensory pathways of the solitariothalamic tract – taste is ____.

Answer 42

nucleus solitarius
ipsilateral
ventral posteromedial nucleus (VPN)
uncrossed

Question 43

Taste

Taste Reflexes
• From the solitary tract, many taste signals are transmitted within the brain stem itself directly into the ____, and these areas transmit signals to the submandibular, sublingual, and parotid glands to help control the secretion of saliva during the ingestion and digestion of food.

Answer 43

superior and inferior salivatory nuclei

Question 44

Taste

Taste Pathways
• From the thalamus, third-order neurons are transmitted to the lower tip of the ____ in the parietal cerebral cortex , where it curls deep into the sylvian fissure , and into the adjacent ____ area.
• This region is rostral to the face area of the ____, which is likely the area that mediates conscious perception of taste and taste discrimination.

Answer 44

postcentral gyrus
opercular insular
postcentral gyrus

Question 45

Taste

Taste preference
• Taste preference can change in accord with the body’s need for certain specific substances.
• For example: Adrenalectomized, salt-depleted animals automatically select drinking water with a high concentration of ____ in preference to pure water and calcium-depleted parathyroidectomized animals automatically choose drinking water with a high concentration of ____.
• Taste preference is likely from a mechanism located in the central nervous system, although the receptors often become sensitized in favor of a needed nutrient.

Answer 45

sodium chloride

calcium chloride

Question 46

Taste

Taste intensity and thresholds
• The ability of humans to discriminate differences in the intensity of tastes, such as intensity discrimination in olfaction, is relatively ____.
• A ____% change in the concentration of the substance being tasted is necessary before an intensity difference can be detected.
• Taste threshold refers to the minimum concentration at which a substance can be perceived.
• ____ taste is much more sensitive, which would be expected, because this sensation provides an important protective function against many dangerous toxins in food.

Answer 46

crude
30
bitter

Question 47

Taste

Taste variations
• Research from the Monell Chemical Senses Research Center revealed that each individual has different gustatory receptor genes that perceive bitterness, and, consequently, carries their own distinctive set of taste receptors, which gives them ____ perceptions.
• People with the most sensitive receptors are 100–1000 times more sensitive to bitterness than the type of people with less sensitive receptors (Bufe et al., 2005).
• It seems that everyone may have their own world of taste.

Answer 47

unique

Question 48

Taste

Miraculin
• A taste-modifier protein, miraculin, has been discovered in a plant. When applied to the tongue, this protein makes ____ taste ____.

Answer 48

acids

sweet

Question 49

Disturbances of Taste

Loss of taste
• The complete loss of taste (____) is ____ encountered, in part because of the large numbers of nerves that relay taste information to the central nervous system. Rarely would a patient have bilateral injury to all the nerves innervating the oropharyngeal region.
• More frequently a patient has ____, decreased taste sensitivity, or ____ (dysgeusia), distortions in the perception of a taste.

Answer 49

ageusia
rarely
hypogeusia
parageusia

Question 50

Disturbances of Taste

Causes
• Most complaints of decreased “taste” function reflect decreased ____ function.
• Impairment of whole mouth gustatory function is rare outside of generalized metabolic disturbances, such as ____, chronic renal failure, end-stage liver disease, thyroid disease, medications, and vitamin and mineral deficiencies.

Answer 50

olfactory

diabetes

Question 51

Disturbances of Taste

Causes
• Taste changes have been documented in the ____ as numbers of taste buds decrease and taste transduction mechanisms become less effective.
• These changes are often accompanied by alterations in ____ habits.
• Taste disturbances are similarly known to occur in patients who receive ____ therapy and chemotherapy and in patients with ____, in whom losses are progressive.

Answer 51

elderly
eating
radiation
diabetes

Question 52

Disturbances of Taste

Taste perception can be altered by:
• ____ invasion of one or more taste nerves
• The release of ____-tasting materials from the nasal and oral cavities secondary to medical conditions and oral appliances (e.g., ____, gingivitis, purulent sialadenitis)
• Transport problems of tastants to the taste buds (e.g., scaring of the ____ surface, mucosal drying, ____ conditions, infections)

Answer 52

viral
foul
rhionsinusitis
lingual
inflammatory

Question 53

Disturbances of Taste
T
aste perception can be altered by:
• Damage to the taste buds (e.g., invasive ____, local trauma)
• Damage to the taste nerves (e.g., ____ damage from Bell palsy, middle ear infections)
• Damage to taste-related central nervous system structures from disorders such as ____, tumors, epilepsy, and stroke.

Answer 53

carcinomas
chorda tympani
multiple sclerosis

Question 54

Disturbances of Taste

Nervous system lesions
• Lesions anywhere along the tract can cause ____ taste deficits.
• An example of a central lesion causing taste deficits is ____ – which can be caused by an embolic stroke to the ____ artery.

Answer 54

ipsilateral
lateral pontine syndrome
anterior inferior cerebellar

Question 55

Disturbances of Taste

Nervous system lesions
• ____ nerve injury after 3rd molar extraction: Taste and sensory dysfunction to ____ of tongue.

Answer 55

lingual

anteiror 2/3

Question 56

Disturbances of Taste

Nervous system lesions
• Unlike CN VII, CN IX is relatively ____ along its path, although iatrogenic interventions can result in CN IX injury (e.g., from ____, bronchoscopy, laryngoscopy, and radiation therapy), and this nerve is not immune to damage from ____, vascular lesions, and infection.
• On rare occasion epilepsy or migraine is associated with a gustatory prodrome or aura, and some tastes may actually trigger ____ or
migraine attacks.

Answer 56

protected
tonsillectomy
tumors
seizures

Question 57

Disturbances of Taste

Medications
• A number of medications have been implicated in taste dysfunction, including ____ agents, antirheumatic drugs, antibiotics, and blood pressure medications.
• ____, a popular antifungal, can produce long-lasting loss of sweet, sour, bitter, and salty taste perception.
• A double-blind study found that ____, a sleep medication, induces a bitter dysgeusia in approxiately two-thirds of individuals tested.

Answer 57

antineoplastic
terbinafine
eszopiclone

Question 58

Disturbances of Taste

Medications
• Alterations in chemosensory function are well- established as a consequence of ____ and chemotherapy for cancer patients.
• Taste thresholds can ____ during chemotherapy and qualitative changes, such as the development of a ____ taste, are frequently reported.

Answer 58

radiation
increase
metallic

Question 59

Disturbances of Taste

Clinical evaluation
• A determination of all the ____ that the patient was taking before and at the time of symptom onset is important, as are comorbid medical conditions potentially associated with taste impairment, such as ____ failure, liver disease, hypothyroidism, diabetes, and dementia.
• Recollection of ____, discharge, nasal obstruction, allergies, and somatic symptoms have potential localizing value.
• Questions related to ____, parkinsonian signs, and seizure should be posed.

Answer 59

mediactions
renal
epistaxis
memory

Question 60

Disturbances of Taste

Clinical evaluation
• Intermittent smell/taste loss usually implies an ____ disorder, such as from rhinosinusitis or other inflammatory problem.
• Sudden smell loss alerts the practitioner to head ____, ischemia, infection, or a psychiatric condition.
• Gradual smell loss can be a marker for the development of a progressive ____ lesion or cumulative ____ effects.

Answer 60

obstructive
trauma
obstructive
drug

Question 61

Disturbances of Taste

Clinical evaluation
• In addition to ____ sensory evaluation, which is key in defining the dysfunction, neurological and otorhinolaryngological examinations, along with appropriate brain and nasosinus imaging, aid in the evaluation of patients with olfactory or gustatory complaints.
• Blood serum tests may be helpful in identifying conditions such as ____, infection, heavy metal exposure, nutritional deficiency (e.g., B6, B12), allergy, and thyroid, liver, and kidney disease.

Answer 61

quantitative

diabetes

Question 62

Disturbances of Taste

Treatment
• Management of chemosensory disorders is condition specific: ____ or surgical interventions are available for most obstructive or inflammatory disorders.
- Candidiasis or other oral infections can be treated with topical ____ and antibiotic treatments.
- Some salty or bitter dysgeusias respond to ____ mouth wash, possibly as a result of its strong positive charge.
- Rhinosinusitis, can be treated with ____ and antibiotics.
- Patients with excessive oral dryness, often benefit from the use of ____, lozenges, or sugarless gum, as well as oral ____ or artificial saliva.

Answer 62

medical
antifungal
chlorohexidine
prednisone
mints
pilocarpine

Question 63

Disturbances of Taste

Treatment
• Medications that induce distortions of smell or taste can often be discontinued, although reversal of the dysfunction may take ____.
• Antioxidants, such as ____ acid, may be effectual in some cases of hyposmia, hypogeusia, dysosmia, dysgeusia, and burning mouth syndrome.
• ____ therapies may improve taste dysfunction secondary to hepatic deficiencies.

Answer 63

alpha-lipoic

zinc and vitamin A

Question 64

Disturbances of Taste

Treatment
• There are reports that some ____ may help some chemosensory disturbances, particularly following head trauma.
• ____ (an acetylcholinesterase inhibitor) has been reported to improve both cognitive and odor identification scores in patients with Alzheimer disease.
• Studies reporting positive effects of ____, acupuncture, and transcranial magnetic stimulation are not convincing and generally lack appropriate control groups.

Answer 64

antiepileptics and antidepressants (amitriptyline)
donepezil
theophylline