GUSTATORY SENSE ANATOMYThe gustatory receptors, which refers to the receptors which initiate the sense of taste, is found within the taste buds. They are highly specialized epithelial cells. They cluster together in the taste buds and are quite responsive to chemical stimuli, thus categorizing them as chemoreceptors. The glossopharyngeal nerve is responsible for transmitting the taste impulses to the parietal lobe of the cerebral cortex. Taste impulses can also be conducted via the facial nerve to the parietal portion of the cerebral cortex. The cerebral cortex then interprets the information.
GUSTATORY SENSE STRUCTUREThe taste buds are present on the tongue and more sparsely present along the walls of the oropharynx and on the soft palate. They are specialized sensory organs, and are small cylinders of many sensory gustatory cells. These cells are then encompassed by supporting cells. The dendrite end of each gustatory cell is known as the gustatory microvillus, which then peeks through the surface that is on the surface of the taste bud known as the taste pore. The gustatory microvilli are the segment of the taste receptor cells that is considered to be the sensitive segment, meaning it responds to stimulus. In order for the gustatory microvillus to respond to chemical stimuli, it requires moisture, and this is where saliva comes in. The combination of saliva and chemical stimulus on the gustatory microvillus creates the sense of taste.
Taste buds are raised, or elevated, from the surrounding tissue by a combination of connective tissue and epithelium. This combination is known as papillae, of which there are three basic types.
Along the rear of the tongue, there are the vallate papillae, which are less numerous than the other types but are also the greatest in size. They take on the shaped of an upside down V.
GUSTATORY SENSE DIAGRAM
Image: Gustatory Sense
The tip of the tongue, and the sides of the tongue, are covered in the fungi-form knob-like papillae known as Fungiform papillae. The back two thirds of the tongue are covered in the papillae known as filiform papillae, which are shorter, thicker, and almost thread like in comparison to the other two forms of papillae.
Not all papillae contain taste buds. The taste buds are not found in the filiform papillae. While the filiform taste buds are the most plentiful, they are not part of the process of taste. The outer cell layers, which are chronically being transformed into scaly projections, are what make the tongue feel hard and rigid along the surface, somewhat like mild sand paper.
GUSTATORY SENSE FUNCTIONSThere are basically only four tastes discerned by the taste buds. Various regions of the tongue are more susceptible to some tastes and less involved in other tastes. The tip of the tongue is most suitable for tasting sweetness. The sides of tongue are prone to taste the sourness while the back of the tongue receives the bitter tastes. Salty tastes can be discerned throughout the tongue, but the sides seem to pick up this taste more than the rest of the tongue. There are those who can discern their tastes to a fine tuned understanding of the large scale and mixed modalities. Wine tasters have been able to detect slight but apparently meaningful differences in the variations of wine tastes.
Hydrogen ions create the taste of sour, which by nature makes all acids taste sour. Sweeter tastes, including sugar, is created through organic molecules, and can vary greatly in their degree of sweetness. The only taste that is truly salty is pure table salt. Other salty tastes are really bitterness disguised with saltiness. Bitterness can be created by quinine as well as what appears to be unrelated molecules. Taste sensations make their way into the brain via two paired cranial nerves. The glossopharyngeal nerves serve the pathway from the anterior portion of the tongue to the brain while the fore section of the tongue is served by the chorda tympani branch that comes from the facial nerve. These nerves take the impulses of taste through the medulla oblongata to the thalamus and then onto the parietal lobe of the cerebral cortex. Once the taste impulses reach the cerebral cortex, the tastes are interpreted.