Taste

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Food flavor is the result of the integration of multiple sensory inputs, including taste, smell, somatosensory sensations (texture, temperature), vision, etc. There are five main taste sensations: bitter, sweet, sour, salty and umami (savory).

When food dissolves in saliva in the oral cavity, chemicals known as tastants interact with specialized gustatory cells located in the taste buds. These taste buds are found on the papillae on the surface of the tongue. About half of the taste buds are in the vallate papillae at the back of the tongue, whereas the foliate and fungiform papillae contain a moderate amount.

Taste buds are barrel-shaped clusters of gustatory epithelial cells located within the papillae. There are five types of gustatory epithelial cells:

• Type I (support): have glial-like support function and are possibly involved in the transduction of salty taste
• Type II (receptor): transduce sweet, bitter or umami taste depending on the receptor expressed
• Type III (presynaptic): transduce sour taste
• Type IV (basal): immature cells that differentiate into other cell types
• Type V (marginal): connect to the surrounding epithelium

When saliva collects in the taste pore on top of a taste bud, the microvilli of the gustatory epithelial cells interact with the tastants dissolved in the saliva. Type II cells, which express specific families of G protein-coupled receptors (GPCRs), bind to sweet, umami or bitter tastants. In contrast, sour and salty taste detection is initiated by direct in intracellular ion concentrations. These intracellular pathways result in cell depolarization and release of neurotransmitters onto afferent gustatory nerves that enter through the basal lamina.

The gustatory afferent fibers then travel via the glossopharyngeal, facial and vagus nerves to synapse in the rostral solitary nucleus in the medulla. From there, the central pathway continues to the ventral posteromedial nucleus of the thalamus to reach the primary gustatory cortex, which is located in the rostral insula and frontal operculum. Within these brain regions, taste sensations are processed and subsequently integrated with other sensory modalities in the orbitofrontal cortex to provide an overall impression of the food.

Find out more about taste transduction in the video below.

Explore concepts

Papillae

Taste transduction starts in the papillae found in the oral cavity. See the images below for a refresher on the anatomy of the lingual papillae.

Taste bud

The taste bud is where chemical stimuli are transduced into electrical signals. Different types of cells are involved in the process.

Taste transduction

The five main taste sensations are transduced via specialized mechanisms. The image gallery below illustrates the main similarities and differences.

Taste neural pathway

Taste signals from the oral cavity are conveyed to the brain through a specific afferent pathway.

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Summary