Chapter 8: The Chemical Senses

Question 1

2 chemical senses

Answer 1

1. gustation
2. olfaction

Question 2

5 major tastes: () – common among many different cultures (box 8.1)

Answer 2

Saltiness, sourness, sweetness, bitterness, and umami (MSG)

Question 3

Poisonous substances—often () -> taste senses offer advantage for survival

Answer 3

bitter

Question 4

factors that contribute to distinguishing countless flavors of food

Answer 4

• activation of different combinations of taste receptors
• distinctive smell
• other sensory modalities: texture, temperature

Question 5

Areas of sensitivity on the tongue: sweetness

Answer 5

tip of the tongue

Question 6

Areas of sensitivity on the tongue: bitterness

Answer 6

back of the tongue

Question 7

Areas of sensitivity on the tongue: saltiness and sourness

Answer 7

sides of the tongue

Question 8

small structures on the upper surface of the tongue that give it its characteristic rough texture

Answer 8

papillae

Question 9

3 different shapes of papillae

Answer 9

1. foliate - back part of sides of tongue
2. vallate - back part of tongue
3. fungiform - front and middle part of tongue

Question 10

major origin of taste sense

Answer 10

taste buds

Question 11

taste buds consist of several ()

Answer 11

taste cells

Question 12

taste cells form chemical and electrical synapses with (1) and (2)

Answer 12

1. gustatory afferent axons
2. basal cells

Question 13

() are found at the base of taste buds

Answer 13

basal cells

Question 14

() bring sensory information from the tongue to dorsal root ganglia

Answer 14

gustatory afferent axons

Question 15

sensory neuron don’t have ()

Answer 15

dendrites

Question 16

At the apical ends of taste buds, taste cells form (1) -> together form (2), which directly interacts with chemicals

Answer 16

1. microvilli
2. taste pore

Question 17

Taste receptor cell membrane potential is usually changed by depolarization, which triggers () that are delivered to gustatory ANs

Answer 17

receptor potentials

Question 18

Most taste receptor cells respond primarily to ().

Answer 18

just one of basic tastes

Question 19

taste stimuli

Answer 19

tastants

Question 20

transduction processes for tastants

Answer 20

1. Pass directly through ion channels
2. Bind to and block ion channels
3. Bind to G-protein-coupled receptors and activate second messengers to open ion channels

Question 21

Tastants open or block ion channels to () taste cell membranes

Answer 21

depolarize

Question 22

If sodium arrives to surface of salt-sensitive taste cells, they pass directly through the (1)

Answer 22

1. selective Na+ channels

Question 23

the selective Na+ channels in salt-sensitive taste cells can be blocked by (1), thus they are also called (2)

Answer 23

1. amiloride
2. amiloride-sensitive Na+ channels

Question 24

the NT released by synaptic vessels in salt and sour-sensitive taste cells is (); this binds to gustatory axon terminals to deliver signal to CNS

Answer 24

serotonin

Question 25

(): causative agents of acidity and sourness

Answer 25

Protons

Question 26

Sourness originates from (1)—>(2)

Answer 26

1. high acidity 2. low pH

Question 27

Protons directly penetrate the () (usually open in sour-sensitive taste cell) to cause H+ influx -> depolarization

Answer 27

H+ channel

Question 28

3 tastes that share common mechanism of signal transduction

Answer 28

bitterness, sweetness, umami

Question 29

the 2 families of taste receptor proteins involved in signal transduction for bitterness, sweetness, umami

Answer 29

T1R and T2R

Question 30

receptors involved in bitterness, sweetness, umami are all ()

Answer 30

GPCRs

Question 31

proteins that make up the bitter receptors

Answer 31

homodimer of T2R receptors

Question 32

proteins that make up sweet receptors

Answer 32

heterodimer of T1R2 and T1R3

Question 33

proteins that make up the umami receptors

Answer 33

heterodimer of T1R1 and T1R3

Question 34

ligand of umami receptors

Answer 34

amino acids (proteins)

Question 35

portion of the thalamus that deals with sensory information in the head

Answer 35

ventral posterior medial (VPM) nucleus

Question 36

cranial nerves (VII, IX, and X) carry () and deliver taste info to the brain

Answer 36

primary gustatory axons

Question 37

taste axons of cranial nerves involved in gustation all enter the brain stem, bundle together, and synapse within the ()

Answer 37

gustatory nucleus

Question 38

the VPM is synapsed by neurons of the ()

Answer 38

gustatory nucleus

Question 39

after receiving signals from the gustatory nucleus, the VPM delivers the signal to the () in the medulla

Answer 39

primary gustatory cortex

Question 40

() - loss of taste perception

Answer 40

Ageusia

Question 41

summary of central taste pathways

Answer 41

Cranial nerves—>gustatory nucleus—>primary gustatory cortex (located in cerebral cortex)

Question 42

ageusia can be caused by () in the VPM, thalamus, or gustatory cortex

Answer 42

localized lesions

Question 43

states that individual taste receptor cells for each stimuli

Answer 43

labeled line hypothesis

Question 44

involves coordination of large number of broadly tuned neurons -> convergence of receptor cell input onto afferent axons

Answer 44

population coding

Question 45

Because population coding takes into account information from other neurons, it may explain the contribution of () to one's perception of food

Answer 45

texture, temperature, smell

Question 46

() in response to a taste/food are distinctly different

Answer 46

overall patterns of discharge (APs)

Question 47

how do we distinguish between tastes (salt vs sour, bitter vs sweet vs umami)

Answer 47

each taste cell selectively expresses only 1 class of taste receptor proteins

Question 48

chemicals released by the body that are important signals for reproductive behavior, territorial boundaries, identification of individuals, etc. in animals but have weak role in humans

Answer 48

pheromones

Question 49

major organ for sensing smell

Answer 49

olfactory epithelium

Question 50

3 types of cells in the olfactory epithelium

Answer 50

1. olfactory receptor cells 2. supporting cells 3. basal cells

Question 51

type of cell in olfactory epithelium: sites of transduction; one of the few types of neurons in the nervous system that are regularly replaced throughout life

Answer 51

olfactory receptor cells

Question 52

type of cell in olfactory epithelium: similar to glia; help produce mucus (produces and maintains mucus layer)

Answer 52

supporting cells

Question 53

why are antibodies important in the mucus layer of the olfactory epithelium

Answer 53

because epithelium is directly exposed to outside (viruses, bacteria, etc.)

Question 54

proteins in olfactory epithelium mucus layer that help concentrate odorants in nucleus

Answer 54

odorant-binding proteins

Question 55

bone that allows innervation of olfactory epithelium by olfactory nerve axons

Answer 55

Cribriform plate

Question 56

activate transduction processes in olfactory neurons

Answer 56

odorants

Question 57

inability to smell

Answer 57

anosmia

Question 58

why do humans have a weak sense of smell

Answer 58

Due to small surface area of olfactory epithelium

Question 59

Ways to terminate Olfactory response

Answer 59

1. Odorants diffuse away 2. breakdown of odorants by scavenger enzymes in mucus 3. cAMP in receptor cell may activate other signaling pathways that end transduction process

Question 60

2 unusual features of olfactory signaling

Answer 60

1. receptor binding proteins at the beginning 2. cAMP-gated channels near the end

Question 61

collectively, the olfactory axons constitute the ()

Answer 61

olfactory nerve (cranial nerve I)

Question 62

small clusters of olfactory axons penetrate the cribriform plate then course into the ()

Answer 62

olfactory bulb

Question 63

in olfactory cells, () is unusually high

Answer 63

intracellular [Cl-]

Question 64

Different odorants are recognized by ()

Answer 64

different receptor proteins

Question 65

Increasing evidence indicates that the only second messenger mediating olfactory transduction in vertebrates is ()

Answer 65

cAMP

Question 66

in most cases, only () is expressed in 1 olfactory receptor cell

Answer 66

1 type of receptor protein

Question 67

olfactory receptor proteins belong to the () family

Answer 67

G protein-coupled receptor

Question 68

G protein in olfactory receptor cells

Answer 68

G_olf

Question 69

like taste, olfaction involves a () scheme to distinguish between smells

Answer 69

population-coding

Question 70

Small spherical structures located in the input layer of olfactory bulbs; spherical forms of axon terminals

Answer 70

glomeruli (glomerulus)

Question 71

each glomerulus contains endings of about 25k (1) that converge and terminate on the dendrites of about 100 (2)

Answer 71

1. primary olfactory axons 2. second-order olfactory neurons

Question 72

Each glomerulus receives input from receptor cells of only ()

Answer 72

1 type

Question 73

() -> molecular labeling method used to visualize mapping of receptor cells onto glomeruli

Answer 73

P2::LacZ knock-mouse

Question 74

output axons of the olfactory bulbs connect directly to several targets, most notably the () (located in primitive region of the cerebral cortex) and some of its neighboring structures in the temporal lobes

Answer 74

olfactory cortex

Question 75

Conscious perception of smell may be mediated by the ff path:

Answer 75

olfactory tubercle -> medial dorsal nucleus (of thalamus) -> orbitofrontal cortex

Question 76

orderly arrangement of neurons that correlates with certain features of the environment

Answer 76

sensory map

Question 77

while a particular odor activated many bulb neurons, the neuron's positions form ()

Answer 77

complex but reproducible spatial patterns

Question 78

the most critical feature of each odorant is its ()

Answer 78

chemical structure

Question 79

each distinct odor triggers activity in ()

Answer 79

a different subset of neurons

Question 80

depends on the timing of AP spikes, might encode the quality of odors

Answer 80

temporal coding