Lecture 15 of Physiological Psych (Taste/Gustation System)

What are the five basic tastes?

Sweet, salty, sour, bitter, and umami

What is the primary function of the bitter taste?

To detect poisons, as many poisonous things are incredibly bitter

Foods such as cheese, soy sauce, and tomatoes are rich in which of the five basic tastes?

Umami

The perception of ‘flavor’ is a combination of what three main sensory inputs?

Taste, smell, and feel (texture and temperature)

The small projections or ‘bumps’ on the tongue are called __________.

Papillae

Which type of papillae are seen as ridges on the tongue?

Foliate

Which type of papillae are seen as pimples on the tongue?

Vallate

Which type of papillae look like mushrooms on the tongue?

Fungiform

Taste buds are located inside what structures on the tongue?

The papillae

Where on the tongue do you mostly taste sweetness?

Front of tongue

Where on the tongue do you mostly taste sour?

Sides of tongue

Where on the tongue do you mostly taste saltiness?

Most surface area of tongue

Where on the tongue do you mostly taste bitterness?

Back of tongue

Which cells are precursors to taste cells?

Basal cells

Odors from food pass via the ________ into the _________.

Pharynx; nasal cavity 

True or false? Olfactory receptors are located high in the nasal cavity.

True

Approximately how many taste receptor cells are found within a single taste bud?

50-150 taste receptor cells

What is the average lifespan of a taste cell?

Two weeks

Are taste receptor cells considered neurons?

No, they are not neurons, but they synapse onto gustatory afferent axons

The microvilli of taste cells project into the _______ to interact with dissolved chemicals.

Taste pore

What is the term for the change in voltage that occurs when a taste receptor cell is activated?

Receptor potential

Activation of sour and salty taste cells leads to the release of which neurotransmitter?

Serotonin (5-HT)

Activation of sweet, bitter, and umami taste cells leads to the release of which signaling molecule?

ATP

Which tastes involves the general transduction mechanism by which taste stimulants directly pass through ion channels?

Salty and sour

Which taste involves the general transduction mechanism of taste stimulants binding to and blocking ion channels?

Sour

Which tastes involves the general transduction mechanism of taste stimulants bind to GCPRs and activate 2nd messengers to open ion channels?

Bitter, sweet, and umami

True or false? Each taste cell is selectively responsive to different tastants.

True

Some taste cells and gustatory axons are ________ or preferentially activated.

Biased

What type of ion channel is responsible for the transduction of salty tastes?

Amiloride-sensitive sodium channels

Regarding saltiness, this refers to anything close to isotonic or 10-150 mM?

Palatable

Regarding saltiness, this refers to being hypertonic; 200mM or higher?

Aversive

What ion channels are insensitive to voltage and generally stay open?

Amiloride-sensitive sodium channels

What is the first transduction step for saltiness?

Higher Na+ outside taste cell

What is the second transduction step for saltiness?

Na+ flows into cell

What is the third transduction step for saltiness?

Membrane depolarizes

What is the fourth transduction step for saltiness?

VGSC and VGCC open

What is the fifth and last transduction step for saltiness?

Neurotransmitters release onto gustatory axons

At high concentrations (e.g., about 200 mM or higher), NaCl activates which other taste cells, leading to an aversive sensation?

Bitter and sour taste cells

For saltiness, what neurotransmitter is released?

Serotonin 

Low pH, caused by acids dissolving in water and generating protons (H+ ions) leads to the sensation of what?

Sourness

One way H+ ions cause depolarization in sour taste cells is by binding to blocking ______ channels.

Potassium (K+)

The transduction of sweet taste relies on which family of taste receptor proteins or dimers?

T1R2 + T1R3

Which family of taste receptor proteins is responsible for detecting bitter tastes?

The T2R family

The transduction of umami relies on which family of taste receptor proteins or dimers?

T1R1 + T1R3

Humans have about how many different T2R receptors to detect a wide variety of bitter substances?

25

In the shared 2nd messenger pathway for sweet, bitter, and umami, G-protein activation stimulates which enzyme?

Phospholipase C

Stimulation of Phosopholipase C increases the intracellular concentration of what molecule?

Inositol triphosphate 3 (IP3)

In sweet/bitter/umami transduction, what is the dual role of IP3?

It opens a taste cell ion channel for Na+ entry and triggers the release of Ca2+ for internal stores

In the sweet/bitter/umami pathway, the release of intracellular Ca2+ activates a membrane channel to release what molecule onto the gustatory axon?

ATP

While sweet and bitter receptors use the same second messenger pathway, they are perceived differently because they are expressed in different taste cells that connect to _________.

Different gustatory axons

What nerve carries taste information from the anterior two-thirds of the tongue?

The facial nerve (CN VII)

What nerve carries taste information from the posterior one-third of the tongue?

The glossopharyngeal nerve (CN IX)

What nerve carries taste information from the epiglottis?

The vagus nerve (CN X)

Axons from the facial, glossopharyngeal, and vagus nerves all synapse in which nucleus in the medulla?

The gustatory nucleus (located in the nucleus of the Solitary Tract or NTS)

From the gustatory nucleus in the medulla, where does taste information travel next?

To the Ventral Posterior Medial (VPM) nucleus of the thalamus

Where is the final destination for taste information in the cortex?

The gustatory cortex

Damage to the gustatory cortex can lead to _______, the loss of taste perception.

Ageusia

Which part of the brain focuses on starvation or overeating?

Hypothalamus

Which part of the brain focuses on palatability?

Amygdala

If the anterior tongue was damaged, you wouldn’t be able to taste what?

Sweetness

The idea that the responses of a large number of broadly tuned neurons are used to specify the properties of a taste stimulus is called __________.

Population coding

What helps an individual to distingue taste?

Different response patterns with large populations of taste cells