Taste and Smell

Sweetness

Indicates energy-rich nutrients and triggered by sugars (glucose, fructose)

Saltiness

Signals mineral content and triggered mostly by Na+ ions

Sourness

Indicates acidity and often associated with spoiled or bacterial activity

Bitterness

Many bitter compounds are alkaloids found in poisonous plants and the body is highly sensitive which leads to a defensive mechanism

Umami

Indicates proteins and amino acids and triggered by MSG and glutamate

Taste buds live inside small structures called ______.

Papillae

Fungiform Papillae is located where?

On anterior 2/3 on tongue

Fungiform Papillae

Each contains up to ~8 taste buds and are visible as small red dots

Foliate Papillae is located where?

Posterior sides of the tongue

Foliate Papillae

Leaf-like folds and contains ~1300 taste buds total

Circumvallate Papillae is located where?

Posterior 1/3

Circumvallate Papillae

Large circular structures and contains ~250 taste buds

Taste buds contain _______, surrounded by support cells

Taste receptor cells

Taste bud structure

Tight junctions prevent saliva chemicals from flooding the cell interior

Taste cells regenerate every ___ to _____ days

10-14 days

Basal cells

Stem cells that regenerate new taste cells

Dark cells

Less mature

Light cells

Fully mature and functional

Intermediate cells

Transitional stages

What is the stimulus of saltiness?

NaCl and other salts

Saltiness mechanism

Requires ionization to Na+ enters taste cell

Saltiness receptor

Sodium channel

Saltiness drug sensitivity

Amiloride blocks Na+ channels that leads to salty taste decreases

When Na+ flows into the receptor cell, it _____ the membrane, triggering neurotransmitter release

Depolarizes

Sourness stimulus

Acids (H+ ions)

Sourness mechanism

Hydrogen ions block K+ channels, normally open K+ channels allow efflux that leads to hyper-polarization, and blocking them leads to depolarization

Less potassium leaving= ? =Fires signal

More positive inside

Sweetness stimulus

Sugars (glucose and fructose)

Sweetness receptor

T1R2 + T1R3

Sweetness is linked to what?

Gustducin (G-protein)

Lower cAMP closes K+ channels which lead to what?

depolarization

Sweetness activates _____ which destroys cAMP

Phosphodiesterase

Bitterness stimulus

Alkaloids (quinine, caffeine)

Bitterness receptor

T2R family (~30 types)

Bitterness mechanism

Gustducin to phosphodiesterase to lower cAMP to close K+ channels to depolarization

Many ____ receptor types exist to detect many possible poisons

Bitterness

Umami stimulus

Amino acids, MSG

Umami receptor

T1R1 + T1R3

Umami mechanism

Uses gustducin and transducin; similar G-protein cascade to sweetness

VII- Facial (chorda tympani)

Anterior 2/3 of tongue

IX- Glossopharyngeal

Posterior 1/3 of tongue

X- Vagus

Epiglottis, plate, pharynx

Taste is _____.

Ipsilateral

Neural Pathway of Taste

1. Cranial nerves

2. Nucleus of the Solitary Tract (NST) in medulla

3. Thalamus

4. Primary Gustatory Cortex (Insula + frontal operculum)

Left tongue

Left brain

Right tongue

Right brain

Olfaction detects ________ in the air.

Volatile chemical molecules

For the Gustatory Cortex Activation, different individuals have _______ activation patterns

Different

____ perception varies slightly person to person.

Taste

Core regions in the ______ and ________ consistently light up.

Insula; Frontal operculum

Humans have ____ odor receptor types

~400

Olfaction is the only sensory system that bypasses the _____ initially

Thalamus

Strong link to emotion and memory because of the _____ connection.

Amygdala

Basic pathway of smell (olfaction)

1. Molecules bind to olfactory receptors in the nasal epithelium

2. Signals travel via Cranial Nerve 1 (Olfactory nerve)

3. Reach olfactory bulb

4. Then to piriform cortex, amygdala, and entorhinal cortex