Pavlos et al. The fungiform papillae were easily distinguishable as they were lightly stained in comparison to the darker filiform papillae. Zhang et al. Photographs of tongue stained with brilliant blue FCF before A and after B fungiform papillae quantification. Reproduced with permission from Jilani et al. Nuessle et al. Using image analysis software and digital photography, the fungiform papillae were then characterised based on their shape, colour, size and height.
Eldeghaidy et al. However, one limitation of this methodology is that the software may inaccurately assess the diameter of the papillae because the software considers all fungiform papillae to be exactly circular in shape. Nutrition and age are two major factors that affect the number of papillae present on the dorsum of the tongue.
Zinc deficiency can also have similar consequences. Due to their high metabolic activity, cells forming filiform and fungiform papillae are also sensitive to enzyme, circulation or nutrient disturbances which can lead to atrophy. During atrophy, filiform papillae are more vulnerable to such disturbances compared to fungiform papillae ; moreover, following atrophy, fungiform papillae regenerate faster in comparison to filiform papillae. Factors potentially resulting in lingual papillae loss Drugs that interfere with the growth and maturation of the epithelium e.
The two primary methods of evaluating taste sensation are chemogustometry and electrogustometry. Chemogustometry involves the application of chemical solutions to the oral mucosa ; subsequently, the degree to which any of the five types of taste presents itself is evaluated by equating the taste with that of a reference material. This is done systematically by either increasing or decreasing the dilution of the substance.
Water is used as a control during the process, with the subject ideally being able to discriminate between water and the diluted test solution. Bitterness is detected by the action of the bitter substance on TAS2R receptors, a type of G protein-linked receptor. Taste transduction is thus induced by the influx of sodium ions in the ENaC receptors which facilitates the release of glutamate to depolarise neurons. Sourness, measured using diluted hydrochloric acid, also acts via the ENaC receptors which allow the inflow of protons and triggers neurons.
Sweetness is assessed using a diluted sweet substance such as sucrose or artificial sweeteners like saccharin, which differ in taste due to their distinct chemical structures. Taste transduction occurs via another G protein receptor known as taste receptor 1. The final type of taste, umami , is savoury in nature. Umami taste is induced by the activation of meta-botropic glutamate receptor 4 as a result of stimulants such as monosodium glutamate.
Inosine monophosphate and guanosine monophosphate act as agonists during umami taste induction. One method of chemogustometric evaluation involves presenting tastants to subjects in a clinical setting via soaked elongated strips or circular disks. Such strips or disks are dissolvable in the oral cavity and do not need to be retrieved afterwards. Using this method, three drops of a chemical tasting solution are placed in the middle of the dorsum of the tongue, approximately 1.
Event-related potentials refer to the electrical responses evoked in the brain when an individual is presented with a stimulus. As such, after applying chemical gustatory stimuli to the tongue, electroencephalography can show cortical brain activity associated with the taste sensation, along with its topographical distribution.
Chemogustometry consists of using an array of chemical solutions in multiple concentrations to assess taste sensation.
Some advantages of this method include the long shelf-life of the materials needed, the ease of administration, the rapidity of testing and the fact that this method allows for evaluation of each side of the tongue separately. Electrogustometry quantifies taste and measures the threshold of taste sensation by passing a controlled current through the tongue using electrodes.
As cathodal stimuli do not produce any significant recordable sensation, a weak anodal current is used. When an electrode from an electrogustometer is placed on tongue, two types of sensations are induced—tingling and taste. Therefore, electrogustometry aids in differentiating between the chorda tympani and lingual nerves and is especially important in determining the integrity of the neural pathway.
Electrogustometry is a quick and quantitative tool to assess taste threshold, particularly among patients with taste disorders such as hemiageusia and ageusia.
Furthermore, electrogustometry can also aid in determining patient prognosis. However, a major drawback of electrogustometry is that it is subjective and relies on feedback from the subject. Finally, this technique cannot be used for patients with artificial pacemakers as electrical stimuli from the electrodes may cause interference with electrical signals from the pacemaker.
Braud et al. Ovesen et al. These findings indicate that electrogustometry could be a useful diagnostic tool in neoplastic cancers. Epstein et al. As such, it is recommended that taste and olfactory electrogustometric evaluations be made mandatory for all patients undergoing cancer treatment. Dzaman et al. Doty et al. The researchers reported a deterioration in taste sensitivity commencing in middle age and progressively reducing after 50 years of age. Boucher et al. Depressed or altered taste sensation has been reported among chronic smokers.
The olfactory nerve, stimulated by smell, helps taste buds communicate the flavors that they absorb to the brain. Colds and other upper respiratory illnesses can affect the olfactory nerve, which can affect smell and taste.
A mild allergic reaction, certain viruses, or even stress can sometimes inflame the papillae in a condition called transient lingual papillitis. Fortunately, this pimple-like irritation is temporary and should go away in a matter of days. A very painful condition related to altered taste buds is burning mouth syndrome. This condition causes a burning sensation on the tongue, palate, and other parts of the mouth and can occur without warning. Burning mouth syndrome affects the ability to detect bitter tastes on the tip of the tongue.
If this sensation is lost, pain receptors in the tongue become overactive. The cause of spontaneous burning mouth syndrome is unknown, but folate, B12 and iron deficiencies, and mouth infections may cause a similar sensation. The papillae are versatile sensory organs that help us enjoy our foods and drinks, so take care of your taste buds. Whatever your favorite flavors are, you need your fungiform papillae to enjoy them. This article is intended to promote understanding of and knowledge about general oral health topics.
It is not intended to be a substitute for professional advice, diagnosis or treatment. Always seek the advice of your dentist or other qualified healthcare provider with any questions you may have regarding a medical condition or treatment.
Shop Now. Figure 4. Umami Umami is the Japanese word for the savory taste of amino acids, such as monosodium glutamate MSG. Salt Salt mechanism has been quite controversial over the last decade. Acknowledgments We would like to thank George Retseck for the illustrations.
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An immunocytochemical and ultrastructural study. Minerva Stomatol. Spatial distribution of rat fungiform papillae. Anat Rec. Brouwer JN, Wiersma A. Location of taste buds in intact taste papillae by a selective staining method. Triantafyllou A, Coulter P. Structural organization of subgemmal neurogenous plaques in foliate papillae of tongue.
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Pharmacol Rev. Lundstrom K. The future of G protein-coupled receptors as targets in drug discovery. The molecular physiology of taste transduction. Curr Opin Neurobiol. Clapp TR, et al. Immunocytochemical evidence for co-expression of Type III IP3 receptor with signaling components of bitter taste transduction. BMC Neurosci. Bessis AS, et al. Closure of the Venus flytrap module of mGlu8 receptor and the activation process: Insights from mutations converting antagonists into agonists.
About taste cells are located in pear-shaped taste buds and the taste cells through microvilli project into a taste pore. There are non-receptor basal cells which are located on the basement membrane which do not project into the taste pore.
These basal cells differentiate through a series of morphological steps into a mature taste cell. The taste cells are replaced about every 10 days.
Transduction of chemical stimuli into nerve impulses begins with saliva transporting the dissolved polar molecules that are sweet or bitter i. Polar molecules do not enter the taste cells, but bind to receptors on the microvilli in the taste pore.
An action potential is then generated in the afferent nerve ending and conducted by the stimulated cranial nerve into the CNS. A similar transduction process converts non-polar solutes into nerve impulses.
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