Final (all lectures that weren't covered previously)

Question 1

Why do we taste?

Answer 1

as an organism, need to eat food to survive, so need an ability to detect good from bad food, nutritious from trash food

• natural selection meant that ancestors who were able to do this survived, passed these genes to us
• sweet, sour, salty, bitter, umami

Question 2

sweet

Answer 2

detects carbs, energy-rich foods

Question 3

umami

Answer 3

detects amino acid-rich foods, foods that are high in protein

Question 4

bitter

Answer 4

detects danger

Question 5

salty

Answer 5

detects electrolytes

Question 6

sour

Answer 6

detects unripened or fermented foods

Question 7

taste detection occurs in the …

Answer 7

… taste buds

Question 8

makeup of the tongue

Answer 8

• glossopharyngeal nerve
• chorda tympani nerve
• papillae (circumvallate, foliate, fungiform)

Question 9

glossopharyngeal nerve (IX)

Answer 9

innervates the back of the tongue

Question 10

chorda tympani nerve (VII)

Answer 10

innervates the front and sides of the tongue

Question 11

the nerves of the tongue go from …

Answer 11

… the tongue to the brain

Question 12

circumvallate

Answer 12

papillae at the back of the tongue

Question 13

foliate

Answer 13

a papillae at the back of the tongue (like circumvallate)

• serous gland produces saliva

Question 14

fungiform

Answer 14

papillae at the front of tongue

• there are 1-5 taste buds/fungiform

Question 15

taste buds

Answer 15

clustered in papillae on the tongue

• contain taste pore (at tip of taste bud), taste cell, basal stem cell, and gustatory afferent nerve (that travel to sensory ganglion)
• taste cells exist in taste bud, taste bud exists in papillae

Question 16

taste cells

Answer 16

• die once every 2-3 weeks
• bind to basal stem cells
• has hundreds of taste receptors/cell
• bring info to brain through gustatory afferent nerve, which eventually converge together to form cranial nerves
• produce AP: chemical transmission, excitable (physiologically, very similar to neurons)
• exist in taste bud

Question 17

taste pore

Answer 17

small opening where tastants bind to

• at tip of taste bud

Question 18

each taste modality is mediated by …

Answer 18

… distinct sensory receptors and cells

Question 19

ion channels allow _____ and _____ to come into cell

Answer 19

sodium (for salty) and hydrogen (for sour) to come into cell

Question 20

GPCR mediates _____, _____, and _____

Answer 20

bitter (T2R), sweet (T1R subfamily), umami (T1R subfamily)

Question 21

T1R2/T1R3 receptors

Answer 21

mediate sweet through this complex

• response of T1R2+T1R3 receptor complexes increases the sweeter the food (shown through graph)
• bind to carbohydrates weakly, so need high sugar concentration (lots of carbohydrates binding) to cause a response in these receptors
• purpose is to detect high energy foods, so want to be sensitive to foods w/ high amounts of sugar

Question 22

T1R subfamilies are defined by a …

Answer 22

… large extracellular domain

• this is what binds to amino acids or carbohydrates, since those are large molecules

Question 23

Where are T1R2/T1R3 receptors co-expressed?

Answer 23

primarily on the circumvallate/foliate papillae

• in a pic, co-expression suggests sweet taste receptors
• each taste cell only expresses one kind of receptor, but each taste bud has many dif. kinds of taste cells

Question 24

T1R1/T1R3

Answer 24

mediates umami (recognizes umami tastants)

• shaped very similarly to sweet receptor b/c in same receptor family, also has large extracellular binding domain
• found primarily in fungiform papillae (lots of co-expression here)

Question 25

IMP

Answer 25

a culinary ingredient that people add to food to make it tastier; when added to amino acids, T1R1/T1R3 response increases (requires some amount of AA to be added w/ it)

• umami receptors bind AA, but binds AA more strongly when IMP is also present
• why adding MSG to foods make it taste better

Question 26

expression of T1R receptors on tongue

Answer 26

sweet and umami mediated by T1R receptor subfamilies

• T1R1 + T1R3 found on fungiform
• T1R2 +T1R3 found on circumvallate
• T1R3 part of both sweet and umami

Question 27

dif. organisms express …

Answer 27

… dif. relevant receptor combos which is driven by evolutionary pressures, what do you need to survive

• e.g. pandas don’t express umami receptors b/c they primarily eat bamboo and not meat, cats lack a sweet receptor, bats lack both sweet and umami receptors b/c they only drink blood

Question 28

family of T2Rs

Answer 28

mediates bitter taste

• extremely diverse family, e.g. T2R5 is specialized to one specific bitter compound
• highly sensitive, so even very very small amounts of compounds will cause strong binding (makes sense, b/c you want to be able to detect even tiny amounts of poison)

Question 29

there are _____ bitter receptors

Answer 29

many different, highly specialized

• Why? B/c poisons can exist in multiple types, poisonous compounds are very diverse, so need diverse bitter receptors
• not black-and-white, e.g. coffee is bitter but many people enjoy it

Question 30

taste cells follow _____ to brain

Answer 30

labeled line

• e.g. sweet cells go to sweet region of brain

Question 31

the same taste cell expresses …

Answer 31

… many kinds of T2Rs

• e.g. both T2R7 and T2R3 are expressed in circumvallate

Question 32

there is a genetic diversity of bitter tasters

Answer 32

humans are highly divergent in how able they are to detect certain compounds (e.g. PROP), the presence of certain genes determines how sensitive you are to detect this

Question 33

taste cells express _____ T1R or T2R, but …

Answer 33

EITHER … different taste cells can exist in the same taste bud

• taste cells are never umami AND sweet, or umami AND bitter
• taste cells detect only one kind of taste, but dif. kinds of taste can exist in the same taste bud

Question 34

ENaC

Answer 34

a Na+ ion channel that detects low concentrations of salt

• salty taste is pleasurable, but high concentrations of salt drive bitter and sour taste receptors

Question 35

OTOP1

Answer 35

the sour taste receptor that detects H+ (makes sense b/c it detects acid, which has H+)

• if expressed in a sweet taste cell, sour things would taste sweet

Question 36

it’s the _____ that fundamentally drive the experience of taste

Answer 36

taste cells themselves

• not the receptors that matter, but the cell that the receptor is in
• by expressing dif. receptors in dif. cells, it is only the identity of the cell that matters (individual taste cells, NOT receptors)
• taste is generated in the brain, not in the periphery

Question 37

gustatory system

Answer 37

each cranial nerve that mediates taste goes to its own unique ganglion

• chorda tympani goes to geniculate ganglion
• glossopharyngeal goes to petrosal ganglion
• pharynx goes to nodose ganglion

Question 38

order of gustatory system

Answer 38

• first order goes from taste receptors on tongue to solitary tract (contains the ganglions)
• second order neuron goes from nucleus of solitary tract (gustatory order) to thalamus
• third order goes from thalamus to gustatory cortex in the intersection of anterior insula and frontal operculum

Question 39

there are separate regions of the brain that represent sweet, bitter, sour, etc.

Answer 39

if you stimulate the cortex, can produce sensation of taste in animals, independent of tastants

• e.g. sweet areas of the gustatory cortex is sufficient to drive sweet response, even w/ nothing in the mouth
• shows that taste is an innate behavior, does not need to be learned

Question 40

flavor depends on …

Answer 40

… taste, smell, and touch

• flavor is a multisensory experience, taste is just one aspect of flavor (but a critical one)

Question 41

taste evolved …

Answer 41

… multiple times in parallel

• many animal experience taste differently, e.g. insects have taste receptors all over their body
• receptors bind to random different things
• important point: animals need to be able to detect food for survival