Ch. 8 Chemical Senses

Front 1

Gustation and Olfaction

Back 1

Taste and Smell. Detect environmental chemicals. Both work together to perceive flavor.

Front 2

Chemoreceptors

Back 2

Chemically sensitive cells distributed all over the body.

Front 3

What are taste preferences based on?

Back 3

-innate preference for sweetness, satisfied by mother's milk.
-innate rejection for bitterness (poisons)

Front 4

Can our instincts be modified?

Back 4

Experience can strongly modify our instincts:
1. We can tolerate or enjoy bitter coffee
2. Our body detects a deficiency of nutrients and develop an appetite for them.(Salty cravings)

Front 5

What are the five tastes?

Back 5

Salty, sweet, sour, bitter and "umami"- delicious. Savory taste of amino acid glutamate- MSG.

Front 6

Gustation and Olfaction

Back 6

Taste and Smell. Detect environmental chemicals. Both work together to perceive flavor.

Front 7

Chemoreceptors

Back 7

Chemically sensitive cells distributed all over the body.

Front 8

What are taste preferences based on?

Back 8

-innate preference for sweetness, satisfied by mother's milk.
-innate rejection for bitterness (poisons)

Front 9

Can our instincts be modified?

Back 9

Experience can strongly modify our instincts:
1. We can tolerate or enjoy bitter coffee
2. Our body detects a deficiency of nutrients and develop an appetite for them.(Salty cravings)

Front 10

What are the five tastes?

Back 10

Salty, sweet, sour, bitter and "umami"- delicious. Savory taste of amino acid glutamate- MSG.

Front 11

What is the chemistry behind taste?

Back 11

Sour- caused by acids
Salts- caused by ionic salts
Sweet- comes from fructose/sucrose, proteins-monellin, artificial sweeteners- saccharin, aspartame. SUGARS least sweet, sweeteners and proteins are 10,000-100,000 sweeter.
Bitter- K+ and Mg+2 caffeine, quinine.

Front 12

How do we perceive chocolate, strawberries, BBQ sauce?

Back 12

1) Combination of basic tastes- unique
2) Most foods have a distinctive flavor as a result of taste and smell occuring simltaneously. (without smell of onion=apple)
3) Sensory modalities like texture, temperature and pain sensations (ie hot pepper-capsaicin)

Front 13

What organs are involved in taste?

Back 13

Pharynx, palate, epiglottis, nasal cavity (olfactory receptors)

Front 14

Papillae

Back 14

Form tastebuds having 50-150 taste receptor cells. They have basal cells surrounding taste cells plust gustatory afferent axons.

Front 15

When can you taste a basic taste stimuli?

Back 15

When concentrations reach a threshold most papillae are sensitive to one basic taste.

Front 16

If single taste receptors show small differences in response to iceream/bananas, how can you distinguish differences between two kinds of chocolate?

Back 16

Apical end- near surface of tongue have thin extensions called microvilli- project into taste pore- taste cell is exposed to stimuli.

Front 17

Taste receptor cells are what?

Back 17

Electrical and chemical synapses onto some basal cells; basal cells synapse onto sensory axons forming info-processing circuit within each taste bud.

Front 18

Receptor Potential

Back 18

Voltage shift when taste receptor cell is activated by an appropriate chemical depolarizing the membrane.
calcium entrers cytoplasm releasing transmitter molecules

Front 19

Transduction

Back 19

Sensory receptor cell electrically responds to an environmental stimulus

Front 20

What taste mechanisms are there? And what basic tastes use what?

Back 20

Tastants (taste stimuli)
1. directly pass through ion channels (salt/sour)
2. Bind to and block ion channels (sour)
3. Bind to G-protein-coupled receptors activating second messenger systems opening ion channels (bitter, sweet, umami)

Front 21

What does saltiness come from?

Back 21

Salt is the taste of Na+ (requires high concentration)

Front 22

Salt Mechanism

Back 22

1. Epithelial cells have amiloride(a drug)-blocked Na+-selective channels.
2. always Open, does not respond to voltage.
3. [Na+] increases outside rceptor cell, gradient across the membrane is steeper. Na+ diffuses down its concentration gradient depolarizing the membrane opening voltage-gated sodium releasing NTs into gustatory afferent axon.

Front 23

Sour Mechanism

Back 23

1. Protons go through amiloride-sensitive sodium channels. Proton current depolarizes cell.
2. Protons block K+ channels depolarizing the cell.

high Acidity low pH=sour taste.

Front 24

Bitter Mechanism

Back 24

1) Bitterness is a signal for poison, cannot distinguish between different bitter tastes because 30 bitter receptors per biter taste

1. Bitter tastant activates G-Protein-coupled receptor stimulating phospholipase C increasing IP3.
2. IP3 activates ion channel that allows sodium to enter depolarizing the cell. causing calcium to enter.
3. IP3 can also trigger Ca+2 release from storage sites. TWO SOURCES trigger NT release stimulating gustatory axon.

Front 25

Sweetness

Back 25

T1R2, TIR3 genes required for taste ability. Chemicals bind activating phospholipase C- Second messenger in better system. Connecting to a different gustatory axon than the bitter (no confusion between tastes)

Front 26

Umami

Back 26

T1R3 shared by the sweet and mami receptors. T1R determines whether receptor is sensitive to amino acids/sweet tastants. Mice lack T1R1 unable to taste amino acids.

Umami, sweet, bitter receptors use same second messenger pathways.

Front 27

Central Taste Pathways

Back 27

Facial nerve, glossopharyngeal nerve, vagus nerve- carry primary gustatory axons and bring taste info to brain.

From gustatory nucleus pathways diverge. Cerebral cortex mediates taste.

Front 28

Ventral Posterial Medial Nucleus

Back 28

Path to neocortex via thalamus (portion dealing with sensory information from head) is common for sensry information.

Front 29

Primary Gustatory Cortex

Back 29

VPM taste neurons send axons to this area- ipsilateral to cranial nerves.