Gustatory System Overview

Gustatory System: Definitions and Overview

• Taste is a chemical sense for detecting dissolved compounds (tastants) in saliva.
• Tastants are water-soluble, molecular substances that stimulate gustatory receptor cells.
• Tastants produce taste sensations by activating taste receptor cells.
• The primary function of taste is to differentiate between food and potentially harmful substances (toxins).

Taste vs. Flavor

• Flavor is a multi-sensory experience integrating taste, smell, texture, temperature, and pain.
• The gustatory system is responsible for taste.
• The olfactory system is responsible for smell.
• The somatosensory system is responsible for texture, temperature, and pain.
• Pleasant flavors are associated with maintaining the appetite and initiating appropriate digestive responses (e.g., saliva secretion).
• Unpleasant flavors are associated with potential toxins, eliciting protective reflexes (e.g., coughing, sneezing, gagging, vomiting).

Stimuli (Tastants) and Taste Submodalities

• Ionized salts (e.g., NaCl): Cations (like Na+) are more important; other cations (K+, Mg2+, Ca2+) also affect taste.
• Acids (e.g., HCl): Sour taste intensity is related to the logarithm of the hydrogen ion concentration.
• Sugars (e.g., glucose, fructose): Organic molecules that elicit sweet taste.
• Organic molecules (e.g., quinine): Alkaloids like quinine evoke a bitter taste.
• L-glutamate: Organic molecules like L-glutamate elicit the umami taste.
• Other molecules (e.g., artificial sweeteners) Also contribute to taste perception.

Distribution of Taste Receptors on the Tongue

• All taste sensations are detected across the entire tongue surface.
• Different regions have higher sensitivity to specific tastes due to differing thresholds of activation for taste buds in those areas.
• Papillae (e.g., circumvallate, foliate, fungiform) house taste buds.

Taste Buds and Taste Receptor Cells

• Taste buds are clusters of cells (~100 cells) sized ~30 x 60 µm in the papillae.
• Taste buds have taste receptor cells, supporting cells, and basal cells.
• Taste receptor cells are modified epithelial cells that synapse with first-order taste neurons.
• These neurons transmit the taste information to the central nervous system.
• Taste receptor proteins can be ionotropic or metabotropic, with specific proteins for each taste.

Basal Cells and Taste Cell Renewal

• Basal cells continually divide to replace taste cells, which have a lifespan of ~10-21 days.
• This continuous cell renewal, called neurogenesis, is unique to these senses.

Distribution of Taste Buds

• Taste buds are primarily located on papillae of the tongue (lingual papillae).
• Other locations include the soft palate, pharynx, larynx, tonsillar pillars, epiglottis, and the proximal esophagus.

Taste Receptor Proteins

• Ionotropic receptors include Na+ channels for Salty and H+ channels for Sour.
• Metabotropic receptors (TR) are involved in Sweet, Bitter, and Umami. Each taste type uses specific combinations of these receptor proteins. Specific receptor proteins (T1R and T2R) are used for the different taste types.

Gustatory Pathways

• Gustatory pathways follow an ipsilateral course conveying taste information.
• The anterior two-thirds of the tongue transmit signals via the facial nerve (VII). The back of the tongue and throat uses the glossopharyngeal nerve(IX) and vagus nerve (X).
• Sensory signals travel to the gustatory cortex for processing.

Rapid Adaptation of Taste

• Taste sensations adapt rapidly, often within a minute or so of continuous stimulation.
• Adaptation occurs both in the taste buds and the central nervous system (CNS).

Taste Preferences and Aversions

• Taste preferences vary based on biochemical needs (body deficiency.)
• Taste aversions develop following a negative experience (getting sick after eating a particular food).

Taste Blindness

• Genetic differences affect an individual's ability to taste certain chemicals, especially thioureas (e.g., PTC).
• About 15-30% of people experience taste blindness with PTC.

Taste Thresholds

• Taste thresholds represent the lowest concentration of a tastant to which taste receptors respond via depolarization.
• Lower thresholds indicate higher sensitivity.

Which Taste has the Lowest Threshold

• Bitter taste has the lowest threshold (highest sensitivity) because it often detects potentially harmful substances.

Relative Taste Indices of Substances

• Taste indices are reciprocals of the taste thresholds for different tastants. These values indicate the relative sensitivity to each substance.

Explore the fascinating world of the gustatory system and its role in taste perception. This quiz covers definitions, the distinction between taste and flavor, and the sensory experiences involved in tasting. Test your knowledge on how the gustatory system helps us identify food and potential toxins.