Chemical Senses (2)

Question 1

Positive chemotaxis is used to what?

Answer 1

find nutrients or locate a mate,

Question 2

Negative chemotaxis does what?

Answer 2

helps us avoid noxious agents such as rotten smells and food.

Question 3

Our nervous system codes for chemicals in our environment by using what?

Answer 3

Labeled Line and Population Coding.

Question 4

What is Labeled Line?

Answer 4

Each chemical is a preferred stimulus which has its own receptor and circuit.

Question 5

Population Coding (Pattern Coding) is what?

Answer 5

Receptors/circuits not ultimately selective. NS analyzes all chemical responses coming in, compares to pinpoint what chemical stimulus might be.

Question 6

What are the different Taste cell types?

Answer 6

Receptor cells- modified epithelial, 50-150 per taste bud; Supporting cells develop into receptor cells. Basal cells develop into supporting cells.

Question 7

What is the innervation of taste cells?

Answer 7

Afferent n. enter buds, end on receptor cells.
Nerves chem synapse on cell, 1:many or many: 1 receptor:nerve; nerves continually remodel synapses on new receptor cell; Receptors degenerate w/o innervation

Question 8

Most of the tongue is sensitive to all basic tastes. What are the exceptions?

Answer 8

receptor can respond to more than one taste, has a preferred taste at threshold levels; Certain regions are more sensitive to specific basic tastes

Question 9

Receptor potentials of taste receptor cells are generated where?

Answer 9

microvilli and apical membrane by a tastant.

Question 10

What does a tasant do?

Answer 10

moves through ion channels or activates a G

protein.

Question 11

What are the characteristics of a taste receptor potential?

Answer 11

graded, changing (depolarizing or hyperpolarizing) by an appropriate chemical

Question 12

Action potentials in the cell body of taste

receptor cells lead to what?

Answer 12

increased Ca2+ influx thru voltage-gated membrane channels w/ release of Ca2+ from intracellular stores-> NT released-> synaptic potentials in dendrites of sensory nerves;

Question 13

How does salty stimuli act on receptor?

Answer 13

tastant mostly Na+ may pass directly thru ion

channels down its concentration; insensitive to voltage; open at rest; inward current causes the membrane to depolarize.

Question 14

How does sour stimuli act on receptor?

Answer 14

Tastant is H+; permeate channel that mediates the salt taste; inward H+ current, cell depolarizes; H+ ions can bind/block a K+-selective channel. When K+ permeability is decreased, cell depolarizes. 2 processes work together

Question 15

How does bitter stimuli act on receptor?

Answer 15

several mechanisms: Some bitter tastants bind directly to K+-selective channels and block them or can activate GPC 2nd messenger cascades.

Question 16

How does sweet stimuli act on receptor?

Answer 16

Sweet molecules bind specific receptor sites (GPCR), activate cascade of 2nd messenger in certain taste cells.

Question 17

How does umami stimuli act on receptor?

Answer 17

Glutamate activates G-protein-coupled 2nd messenger cascades in certain taste cells; meaty flavor

Question 18

How is intensity of taste coded?

Answer 18

greater the amount of tastant, the faster the

firing rate of afferent fibers

Question 19

What is taste pattern coding?

Answer 19

Each taste cell responds differently to four tastants

Question 20

What is population coding of taste?

Answer 20

responses of 4 taste cells to 4 different tastants; combined in brain to determine
the final taste

Question 21

What other senses are involved in taste sensation?

Answer 21

vision first, tactile, taste, olfaction, Thermal, irritative, kinaesthetic and auditory patterns

Question 22

What other than sensory modalities effects taste perception?

Answer 22

adaptation, memory and conditioning; Taste is acquired;

Question 23

Aguesia results in what?

Answer 23

effects control of feeding and digestion; control of body weight may be difficult

Question 24

At low concentrations of an odor what is the sensation? high concentrations?

Answer 24

smell sensation is unspecific; specific

Question 25

What are the 6 primary smells?

Answer 25

floral, fruit, spicy, resin, burnt, and putrid

Question 26

Olfactory receptors are what in the neural pathway?

Answer 26

primary afferent neuron; both the transducer and encoder of the signal

Question 27

Chemosensory transduction takes place where?

Answer 27

mucus lining the surface

Question 28

What are the characteristics of the olfactory receptor?

Answer 28

short peripheral process extends to surface of mucosa, long central process runs from nasal cavity to olfactory bulb (unmyelinated axons slow AP), turnover every 4-8 weeks

Question 29

What is the role of the supporting cells?

Answer 29

produce mucus; flows constantly replaced every 10 minutes.

Question 30

What is the role of mucus in smell?

Answer 30

Odorants dissolve in mucus b4 receptor, water base with dissolved salts, mucopolysaccharides and odorant-binding proteins.

Question 31

odorant-binding proteins contribute to what?

Answer 31

odorant concentration or removal