Wednesday, December 2, 2009

Taste bud ..


Taste buds:


Are small structures on the upper surface of the tongue, soft palate, upper esophagus and epiglottis that provide information about the taste of food being eaten. These structures are involved in detecting the five elements of taste perception: salty, sour, bitter, sweet, and umami (or savory). Via small openings in the tongue epithelium, called taste pores, parts of the food dissolved in saliva come into contact with taste receptors. These are located on top of the taste receptor cells that constitute the taste buds. The taste receptor cells send information detected by clusters of various receptors and ion channels to the gustatory areas of the brain via the seventh, ninth and tenth cranial nerves.



On average, the human tongue has 2,000–8,000 taste buds.[1]

Types of papillae:


The majority of taste buds on the tongue sit on raised protrusions of the tongue surface called papillae. There are four types of papillae present in the human tongue:






Fungiform papillae - as the name suggests, these are slightly mushroom-shaped if looked at in longitudinal section. These are present mostly at the apex (tip) of the tongue, as well as at the sides. Innervated by facial nerve.






• Filiform papillae - these are thin, long papillae "V"-shaped cones that don't contain taste buds but are the most numerous. These papillae are mechanical and not involved in gustation. Characterized increased keratinization.







• Foliate papillae - these are ridges and grooves towards the posterior part of the tongue found on lateral margins. Innervated by facial nerve (anterior papillae) and glossopharyngeal nerve (posterior papillae).







• Circumvallate papillae - there are only about 3-14 of these papillae on most people, and they are present at the back of the oral part of the tongue. They are arranged in a circular-shaped row just in front of the sulcus terminalis of the tongue. They are associated with ducts of Von Ebner's glands. Innervated by the glossopharyngeal nerve.






It is known that there are five taste sensations:

Sweet, Bitter, and Umami (now sometimes called Savory), which work with a signal through a G protein-coupled receptor.
Salty and Sour, which work with ion channels.

Localization of taste and the human "tongue map":
Contrary to popular understanding that different tastes map to different areas of the tongue, taste qualities are found in all areas of the tongue, although some regions are more sensitive than others.[2][3]
The original "tongue map" was based on a mistranslation by Harvard psychologist Edwin G. Boring of a German paper that was written in 1901.[4] Varying sensitivity to all tastes occurs across the whole tongue and indeed to other regions of the mouth where there are taste buds (epiglottis, soft palate).[5]


Structure of taste buds:
Each taste bud is flask-like in shape, its broad base resting on the corium, and its neck opening, the gustatory pore, between the cells of the epithelium.
The bud is formed by two kinds of cells: supporting cells and gustatory cells.

• The supporting (sustentacular) cells are mostly arranged like the staves of a cask, and form an outer envelope for the bud. Some, however, are found in the interior of the bud between the gustatory cells.
• The gustatory (taste) cells, a chemoreceptor, occupy the central portion of the bud; they are spindle-shaped, and each possesses a large spherical nucleus near the middle of the cell.

The peripheral end of the cell terminates at the gustatory pore in a fine hair filament, the gustatory hair. Some early experimental studies (Kirk and Grills, 1992)it was shown that subjects who were genetically predisposed to baldness were found to be 78% more likely to experience taste loss sensations in 5 out of 5 taste trials (p <>
References
1. ^ Encyclopædia Britannica. 2009. Encyclopædia Britannica Online.
2. ^ Huang A. L., et al. ""The cells and logic for mammalian sour taste detection"". http://www.nature.com/nature/journal/v442/n7105/abs/nature05084.html., Nature, 442. 934 - 938 (2006).
3. ^ Scenta. "How sour taste buds grow". http://www.scenta.co.uk/scenta/news.cfm?cit_id=1061938&FAArea1=widgets.content_view_1. Retrieved August 28 2006.
4. ^ Hänig, D.P., 1901. Zur Psychophysik des Geschmackssinnes. Philosophische Studien, 17: 576-623.
5. ^ Collings, V.B., 1974. Human Taste Response as a Function of Locus of Stimulation on the Tongue and Soft Palate. Perception & Psychophysics, 16: 169-174.
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