Gustation | Sensing the environment | Psych/soc

The sense of taste—known scientifically as gustation—encompasses a limited set of recognized submodalities. Historically, only four tastes were acknowledged: sweet, salty, sour, and bitter. Later research introduced umami (from the Japanese term for “delicious taste”), often described as a savory flavor. Recent findings indicate there may also be a sixth taste for fats (lipids).

Taste receptors and papillae

Gustation is associated with the tongue, which is lined by stratified squamous epithelium throughout the oral cavity. Raised bumps on the tongue’s surface, called papillae (singular: papilla), house the structures necessary for taste transduction.

The four types of papillae contain taste buds with gustatory receptor cells:

Circumvallate
Foliate
Filiform
fungiform

These specialized cells detect chemical components in food and release neurotransmitters proportionate to the chemical’s concentration.

Sensory neurons from the facial, glossopharyngeal, and vagus cranial nerves synapse with these receptor cells.

Tongue papillae and taste bud structure for gustation

Salty and sour tastes

Salty Perceived when sodium ions (Na+) in saliva enter gustatory cells, causing membrane depolarization.
Sour Associated with hydrogen ions (H+), representing acidic content. Increasing H+ lowers pH, generating stronger receptor potentials.

Sweet, bitter, and umami tastes: These three tastes involve molecules binding to a G protein–coupled receptor:

Sweet

Triggered by glucose, other monosaccharides, and artificial sweeteners (e.g., aspartame, saccharine, sucralose).

Bitter

Elicited by diverse bitter-tasting molecules, including alkaloids commonly found in plants (e.g., coffee, tea). These can either depolarize or hyperpolarize gustatory cells, depending on the molecule.
Thought to protect against ingesting poisonous substances by activating the gag reflex.

Umami

Caused by L-glutamate, an amino acid found in protein-rich foods, contributing to the savory taste experience.

Neural pathways

Activated gustatory receptor cells release neurotransmitters onto sensory neurons. These neurons belong to the:

Facial nerve (anterior portion of the tongue)
Glossopharyngeal nerve (posterior portion of the tongue)
Vagus nerve (extreme posterior region near the pharynx, crucial for the gag reflex)

These nerves relay taste signals to the brain, allowing us to perceive and respond to various flavor molecules.