Psyc 362Chapter 7 text-Audition, the body senses, and the chemical sensesGustationThe Stimuli● Helps us determine the nature of things we put in our mouth based on chemicals. ● For a substance to be tasted, molecules of it must dissolve in the saliva and stimulate the taste receptors on the tongue. ● 6 qualities of taste: bitterness, sourness, sweetness, saltiness, unami and fat.○ Sweetness receptors are food detectors for mostly safe foods○ Saltiness detect presence of sodium chloride, important mineral for many animals. Bleeding also causing salt lose, so animals must be capable of detecting it.○ unami (good taste) refers to the taste of monosodium glutamate (MSG), a substance often used as a flavor enhancer in asian cuisine. Umami receptors detect the presence of glutamate, an amino acid found in proteins and provide the ability to taste proteins.○ Because of bacterial activity, many foods become acidic when they soil, in addition, most unripe fruits are acidic. Acidity tastes Sour and causes avoidance! Bitterness is almost universally avoided and cannot easily be improved by addingsome sweetness. Ex: Alkaloids taste bitter, thus bitterness receptors undoubtedlyserve to warn animals away from these chemicals. ○ Preference for high-fat foods for many animals. When fasts reach the tongue, some of these molecules are broken down into fatty acids by a lingual lipase enzyme found in the vicinity of taste buds. This ensures that fatty acid detectors are stimulated when food containing fat centers the mouth. ■ Two G-protein receptors appear responsible for detecting fatty acids in the mouth● Flavor (not taste) is a composite of olfaction and gustation, because much of the flavor depends on odor. Anatomy of the Taste Buds and Gustatory Cells● Taste buds contained in the tongue, palate, pharynx, and larynx as arranged around papillae (small protuberances of the tongue). ● Taste buds consist of groups of receptor cells with cilia located at the end of each cell that project through the opening of the taste bud (the pore) into the saliva that coats the tongue. ● Taste receptor cells form synapses with dendrites of bipolar neurons with axons conveying gustatory info to the brain through several cranial nerves. Receptor cells are short lived in a rather hostile environment, and are replaced by newly developed cells.Perception of Gustatory Information● Tasted molecules bind with receptors and produce changes in membrane permeability that cause receptor potentials (transduction of taste much like chemical transmission at synapses)○ Salty tastes produced by a substance that ionizes, best done by NaCl but just has to have a metallic cation with a small anion. The receptor seems to be asimple sodium channel, such that sodium present in saliva enters the taste cell and depolarizes it, causing an AP and release of NTs.○ Sourness receptors respond to hydrogen ions present in acidic solutions, such that the anions have an effect. ○ Bitterness typically detected by a plant alkaloid stimulus, or other poisonous compounds. Like 30 different receptors○ Sweetness is typically stimulated by a sugar like glucose or fructose. Two different receptors are responsible. The Gustatory Pathway● The nucleus of the solitary tract in the medulla receives info from visceral organs and from the gustatory system. This nucleus has axons sending to the ventral posteromedial thalamic nucleus. Thalamic taste-sensitive neurons also send their axons to the primary gustatory cortex, located in teh base of the frontal cortex and in the insular cortex. From there, neurons project to the secondary gutatory cortex in the caudolateral orbitofrontal cortex. ● Taste is ipsilaterally represented in the brain.Plus, tasting of different flavors activatesdifferent areas of the regions of the primary gustatory area of the insular cortex. ● The gustatory cortex also receives thermal, mechanical , visceral, and nociceptive (painful) stimuli. This helps determine palatability of