3 - Grover - Chemosensory Function

Question 1

What are the stages to olfactory chemoreceptor depolarization?

Answer 1

1. Odorant bdinging to G_OLF
2. Stimulation of Target (adenylyl cyclase, cAMP increase)
3. cAMP Gated Cation Channels Open (depolarization, inward +)
4. Ca²⁺ Gated Chloride Channels Open (depolarization, outward -)

Question 2

Why is there a Chloride (Cl^-) current in olfactory receptor neurons?

Answer 2

E_Cl is pisitive to threshold

Result is a depolarizing current–chloride flows out gated calcium channels

Question 3

How does olfaction adapt?

Answer 3

Ca²⁺ binds to calmodulin

[Ca²⁺ - Calmodulin] Complex inhibits CNG (cyclic nucleotide gated) Channels

Question 4

CNG Channels

Answer 4

Cyclic Nucleotide Gated Channels

Activated by cAMP in olfactory receptors

Ca²⁺ , Na⁺ enter cell

Inhibited by [Calcium-Calmodulin] Complex

Question 5

How many receptor proteins does each olfactory receptor neuron represent?

Answer 5

One

Each protein is the product of a distinct gene

Question 6

How many odors can humans differentiate?

How can humans differentiate more odors than unique genes?

Answer 6

>20,000

Population Coding

Question 7

Population Coding

Answer 7

Increase number of unique signals differentiated

For a single receptor protein, strength of activation varies depending on odorant

Each odorant leads to a unique activity pattern

Question 8

Frequency Coding (olfactory)

Answer 8

Intensity of an ordor (concentration of odorant molecules) is represented by firing rate

Higher concentration = faster action potential generation

Question 9

Where does axon sorting occur in olfactory?

Why do some smells contain common “features” or connections?

Answer 9

Olfactory Bulb

All receptor neurons innervating on glomerulus contain the same olfactory receptor protein

Question 10

Whre does signal amplification occur (smell)?

Answer 10

Olfactory Bulbs

convergence of many receptor neurons

Question 11

What type of cells are taste receptor cells?

Where are these located?

How are these cells connected to afferent cells?

Answer 11

Epithelial, not neuronal

Contained within taste buds, whuch cluster into papullae on surface of tongue

Connected to gustatory afferent axon by synapse

Question 12

Five Basic Taste Profiles

Answer 12

Salt

Bitter

Sour

Sweet

Umami

Question 13

How many tastes do taste receptor cells respond to?

How is this related to the Gustatory Afferent Axon?

Answer 13

Individuals receptor responds to one basic category of taste

- - -

Gustatory Afferent Axons may innervate multiple receptors, so it may be triggered by multiple basic categories of taste. If it only innervates one, it will only repond to one.

Afferent axons are a messenger, they do not discriminate

Question 14

Salt and Sour Transduction

Answer 14

Ionotropic

Question 15

Sweet, Bitter, Umami Taste Transduction

Answer 15

Metabotropic - G-Protein Coupled

Question 16

What rises if gustatory response is sufficient?

Answer 16

Intracellular calcium rises

transmitter released (serotonin, ATP, Gaba?)

Afferent axon firing rate changes

Question 17

Salt Taste Transduction

Answer 17

1. Epithelial Sodium Channel (ENaC) Leak Channel is voltage sensitive, always open
2. Na+ Influx (depolarization)
3. Voltage-gated Ca²⁺ Channels Open
4. Transmitter release

Amiloride inhibits

Question 18

Sour Taste Transduction

Answer 18

Proton permeable TRP Channel

1. Sour food increase H⁺ concentration outside apical membrane
2. Acid stimulates TRP channel to open (H+ influx, depolarization)
3. Voltage-gated Ca²⁺ Channels Open
4. Neurotransmitter release

Question 19

Sweet Taste Transduction

Answer 19

Bind to G-protein coupled receptor

1. G-Protein Stimulates Phospholipase C (PLC)
2. PLC Catalyzes formation of IP₃
   3a: Ca²⁺ TRP Channel Activated
   3b: Intracellular released of Ca²⁺
3. Neurotransmitter release (calcium dependent)

Question 20

Bitter and Umami Taste Transduction

Answer 20

Same as sweet, but use different G-protein receptors

Bitter = Gustducin