Gustatory System PDF

Gustatory system Asghar Ghasemi Professor of Physiology Shahid Beheshti University of Medical Sciences  Definitions Taste sensation is a chemical sense, specialized for the detection of compounds (tastants) dissolved in the saliva. Tastant: W...

Gustatory system Asghar Ghasemi Professor of Physiology Shahid Beheshti University of Medical Sciences  Definitions Taste sensation is a chemical sense, specialized for the detection of compounds (tastants) dissolved in the saliva. Tastant: Water-soluble chemicals (molecular substance) that stimulate gustatory receptor cells are known as tastants. Tastant is a substance that produces a taste sensation by activating taste receptor cells The elemental role of gustatory sense or taste sense (gust = taste) is to distinguish between food and potential toxins.  Taste vs. flavor (flavour) Taste is an essential component of flavor Flavor is a multi-modal and integrated sensory experience of taste, smell, texture, temperature, and even pain from a food Distribution area of taste on the surface of the tongue The entire tongue surface detects all forms of taste Different regions of the tongue are more sensitive to one taste over another because the taste buds in that region have a lower threshold of activation for that specific stimulus quality  Taste receptor proteins are Papillae are membrane proteins (ionotropic and specialized epithelial metabotropic) structures on the surface of the tongue which house the taste buds Taste buds are cluster Taste cells are of cells (~100 cells) modified with a size of 30 × 60 epithelial cells µm) arranged like that synapse slices of an orange with first-order with a central opening taste neurons of (taste pore) open to the gustatory the surface of the pathway and tongue and house house taste taste cells receptor proteins Papillae Posterior aspect of the tongue (~ 50%) Lateral and posterior margins of the tongue (~ 25%) Anterior two-thirds of the tongue dorsum (~ 25%)  Taste buds Children: >10000 Adults: 3000-10000 (~5000) Beyond the age of 45 years, many taste buds degenerate, causing taste sensitivity to decrease in old age. Each taste bud has three types of cells: 1. Taste receptor cells 2. Basal cells 3. Supporting cells What is the function of basal cells? The average life span of each taste cell is ~10 days (2-21) The taste cells are continually being replaced by mitotic division of basal cells some taste cells are young and others are mature cells. Because taste and smell receptors are constantly exposed to harmful materials such as bacteria and dirt, they undergo a cycle of birth, development, and death. This constant renewal of the receptors, called neurogenesis, is unique to these senses.  Distribution of taste buds Main location: Papillae of the tongue (lingual papillae) Other locations: Soft palate Pharynx Larynx Tonsillar pillars Epiglottis Proximal esophagus Taste receptor proteins ENa channels Salty Ionotropic taste receptors Hydrogen-ion Sour selective channel (Otopetrin 1) T1R1 Umami (T1R1+T1R3) Metabotropic taste T1R T1R2 Sweet receptors (TR) (T1R2+T1R3) T1R3 T2R Bitter ENa: Epithelial Na channels=ASC=Amiloride-sensitive channels Gustatory pathway Anterior two-thirds of the tongue→ ack of the tongue and posterior regions of the mouth and throat → Base of the tongue and other parts of the pharyngeal region →X (Gustator y/taste nucleus) N. VII: Facial nerve N. IX: Glossopharryngeal nerve N. XL Vagus nerve  Unique to gustation, all gustatory pathways follow an ipsilateral course — meaning that taste information from the right side of the tongue is processed on the right side of the cortex  Rapid Adaptation of Taste Taste sensations adapt rapidly, often almost completely, within a minute or so of continuous stimulation: Adaptation of the taste buds (50%) Adaptation in the CNS (50%)  Taste preference and taste aversion (negative taste preference) means that an animal will choose certain types of food in preference to others according to body’ s need. If a person becomes sick soon after eating a particular type of food, the person then generally develops a negative taste preference (taste aversion) for that particular food.  Taste Blindness Genetic differences affect people’ s ability to sense the taste of certain substances. Some people are taste-blind for certain substances, especially for different types of thiourea compounds. One of the best-documented effects involves people’ s ability to taste the bitter substance phenylthiocarbamide (PTC). PTC is used by psychologists for demonstrating taste blindness About 15-30% of all people exhibit taste blindness for PTC.  Taste Thresholds Tase threshold is the lowest concentration of a tastant to which the taste receptors respond by depolarization. The lower the taste threshold, the higher the sensitivity to the substance  Which of the taste modalities has the lowest threshold (highest sensitivity) and what is its importance? Bitter Importance: Poisonous substances are often bitter and the low threshold (or high sensitivity) of bitter taste have a protective function.  Taste indices Taste indices are the reciprocals of the taste thresholds Thank you