5o8 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY I 



FIG. I. Dorsal surface of the tongue partially dissected to 

 show the nerves to the posterior part. The circumvallate (C), 

 fungiform (F«) and filiform (F;) papillae are shown. The 

 foliate papillae QFo} are not clearly visible in this view since 

 they are on the lateral surface of the tongue. Taste buds occur 

 in C, Fo and not in Fi. [From Warren & Carmichael (199).] 



in diameter al the thickest part. In a wide variety of 

 species these values range from 27 to 1 15 m for length 

 and 14 to 70 M for width. Two kinds of cells have 

 been described, a) the thicker supporting cells and 

 ft) the more slender gustatory cells from which a fine 

 terminal hair projects into the taste pore, but these 

 may be different stages in the age or functional state 

 of but a single type (124). During maturity a con- 

 tinuous process of atrophv and growth maintains the 

 population of receptor cells at a relatively stable level. 



In children, taste buds are more widely distributed 

 o\er the hard palate, soft palate, pharyngeal walls 

 and fungiform papillae of the middorsum of the 

 tongue. In the adult, fungiform papillae are restricted 

 to the sides and edges of the anterior tongue (198). 

 Each fungiform papilla contains 3 to 4 taste buds. 

 Taste i)uds of the circumvallate papillae show a 

 marked atrophy in old age (i i). The total numijer of 

 taste buds in man is probai^ly of the order of 10,000. 

 It has been suggested that in humans the taste papil- 

 lae reach full development at puberty and remain so 

 until the age of 45 when regressixe changes set in (4). 

 In aniiuals atrophic changes followed castration but 

 could be reversed by hormone replacement therapy 

 (5). Such atrophic changes, howe\'er, do not appear 

 to diminish taste sensitivity in a preference test (184; 

 Warren, R. P. & C. Pfaflfman, unpuiilished oi)serva- 

 tions). In man the decrease in number of taste buds 

 with age is correlated with a decrease in sensitivity. 

 Young adults recognized sugar solutions at a lower 

 mean threshold, 0.41 per cent (0.012 m) compared 

 to 1.23 per cent (036 m) for elderly subjects (179). 



The taste cell is a modified epithelial cell. The 

 taste buds degenerate and disappear entirely after 



FIG. 2. Golgi preparations of taste buds and associated nerve endings. A. Taste cells and a 'sus- 

 tentive' element. B. Nerve endings, sense cells not shown (after Retzius). [From Crozier (62).] 



Taste buds are goblet-shaped clusters of cells 

 oriented vertically in the epithelial layer with a small 

 pore opening to the mucosal surface (fig. 2). Human 

 taste i)uds measure from 60 to 80 ^i in length and 40 fx 



section of the taste afferent fibers. When nerve fibers 

 regenerate to the periphery, taste buds also regenerate 



('49. 152)- 



Intrageminal nerve fibers arise from a subepithelial 



