Week 6: Chemical Senses

Question 1

List the basic tastes.

Answer 1

Umami
Sweetness
Bitterness 
Saltiness 
Sourness

Question 2

Describe the basic structure of a taste bud

Answer 2

Taste buds consist of an apical end (which is in the environment), microvilli with tight junctions between (which protects the concentration of exracellular fluids) in the taste pore. Taste cells fit behind the taste pore, with basal cells behind that. Gustatory afferent axons adjoin with a synapse to the taste cells.

Question 3

Which of the following is NOT a chemical sense?

a. Vestibular
b. Gustation
c. Olfaction
d. Chemoreceptors

Answer 3

a. Vestibular

Question 4

Umami receptors respond to:

a. short-chain carbohydrates
b. monosodium glutamate
c. Na+
d. H+

Answer 4

b. monosodium glutamate

Question 5

Taste stimuli interact with apical membrane by (select all that apply):

a. releasing neurotransmitters
b. showing highly specific ligand binding patterns
c. binding to specific membrane receptors
d. directly modulating ion channels

Answer 5

c. binding to specific membrane receptors

d. directly modulating ion channels

Question 6

Describe the transduction mechanism for sour tastants

Answer 6

H+ ions either diffuse
through amiloride sensitive
Na+ channels or act directly
on K+ channels which close:
Depolarization opens
voltage gated Ca++ channels

Other mechanisms may exist also

Question 7

List the nerves involved in central taste pathways.

Answer 7

• Cranial nerves VII, IX and X

Question 8

Ions like K+ and Mg2+, quinine, and caffeine correspond with:

a. Umami
b. Sweetness
c. Bitterness
d. Saltiness
e. Sourness

Answer 8

c. Bitterness

Question 9

True/false: Individual taste receptor cells are specific to a single tastant

Answer 9

FALSE

Individual taste receptor cells are mostly tuned to
a single tastant, but many are not specific (e.g. sour and salt)

Question 10

Where does the gustatory nucleus project to in the Central taste pathway?

Answer 10

The VPM of the thalamus, which relays the info to the gustatory cortex.

Question 11

Taste stimuli are received by a receptor ion channel, which causes:

a. Transmitter release
b. Hyperpolarization
c. Dark currents
d. Conductance change

Answer 11

d. Conductance change

Question 12

H+ corresponds with:

a. Umami
b. Sweetness
c. Bitterness
d. Saltiness
e. Sourness

Answer 12

e. Sourness

Question 13

Which of the following is NOT a receptor cell in taste buds:

a. Dark cells (D)
b. Light cells (L)
c. Intermediate cells (I)
d. Bright cells (B)

Answer 13

d. Bright cells (B)

Question 14

Umami, bitter and sweet transduction processes usually involve tastants that:

a. Pass directly through ion channels
b. Bind to and block ion channels
c. Bind to G-protein-coupled receptors and activate
second messenger to open ion channels

Answer 14

c. Bind to G-protein-coupled receptors and activate

second messenger to open ion channels

Question 15

True or false: Receptor cells respond to different taste

stimuli and show different responsiveness

Answer 15

TRUE Receptor cells respond to different taste

stimuli and show different responsiveness

Question 16

Which of the following is often a neurotransmitter for taste buds?

a. 5-HT (serotonin)
b. Glutamate
c. GABA
d. Noradrenaline

Answer 16

a. 5-HT (serotonin)

Question 17

Which tastant acts directly
on Na+ ion channels, which are always open, and leads to depolarization which
causes voltage gated
Ca++ channels to open?

a. Umami
b. Sweetness
c. Bitterness
d. Saltiness
e. Sourness

Answer 17

d. Saltiness