Sense of Taste (Gustation)(\(),Y1'

The taste receptors or taste buds, about 9.000 in the adult, u.e,placed mainly on theadult,

peripheral parts of the dorsurn of the tongue, being most leteMy found in the groove surrounding the vallate papillae ; some is occur on the soft palate and a few on the epiglottis4n the child they are much atore numerous and much more widely distributsel over the Tongue and on the tigideSof the cheeks. :The oval taste buds embstratified epithelium covering the tongue contain fusiform taste cells strrotindedsby' supporting cells like the staves of a barrel., -'ach taste cell ends in a gustatory hair which passes up towards the minute opening of the taste bud (gustatory pore) upon the surface._

The nerves of taste are the lingual branch of the glossopharyngeal for the posterior third of the tongue, including the vallate papillae, while the anterior two-thirds are served by the" chorda tympani branch of the facial. The greater superficial petrosal nerve supplies gustatory fibres to the palate. Taste buds near the epiglottis are innervated by the vagus, All the nerve fibres pass centrally to the tractus solitaries, a long column of grey matter in the medulla oblongata. From. here fibres cross the mid-line and pass to the posterior ventral nucleus of the thalamus and then on to the lower parts of the post-central gyros and probably other areas nearby. The lingual branch of the fifth nerve is the nerve of common sensibility for the anterior two-thirds of the tongue ; the lingual branch of the glossopharyngeal carries both taste and' common sensibility fibres for the posterior third.

Probably no true taste fibres pass into the brain stern by the fifth nerve but tactile, pain and thermal sensations conveyed by this nerve play an important part in the recognition of taste sensations. The integration of taste sensations of the chorda with common sensibility conveyed by the fifth nerve provides a full gustatory experience. When the fifth nerve in man is cut or destroyed the sense of taste is immediately lost in the front of the tongue but it returns in some cases after a few hours, in other after years. There is no such separation of routes for taste and common sensibility from the posterior part of the tongue as both enter the brain stem by the glossopharyngeal nerve. If the facial nerve is divided above its ganglion the sensation of taste is lost permanently on both the palate and the interior part of the tongue ; although the fifth nerve is intact, it 'is unable to provide a sensation of taste.

There are only four tastes, namely sweet, sour, salt and bitter. Sweet tastes are most easily perceived at the tip of the tongue, bitter at the back, sour at the edge and salt both at the tip and the edge. It is not possible to test single taste buds since they are arranged in groups. The full sensation allowing the taste to be correctly recognized may not appear for several seconds. This is in complete contrast to light and auditory stimuli which are recognized after a very short latent period. Tastes in everyday life are generally a mixture of gustatory, tactile, thermal, kinaesthetic and olfactory sensations.

The temperature of the food affects gustation. Food has often more flavour when it is hot ; iced food needs much flavouring.