Main regions of the tongue.
A microscopic view of the surface of the tongue.
Top: fungiform papillae. These mushroom-shaped papillae
occur in small numbers at random over the tongue surface mainly at
the tip and sides.
Bottom: filiform papillae. These, smaller, peaked-shaped protuberances occur in large numbers over all except the back of the tongue's upper surface, and on the palate.
The tongue is a muscular organ on the floor of the mouth in most higher vertebrates that carries taste buds (see taste) and manipulates food. It may act as a tactile or prehensile organ in some species. In some advanced vertebrates, the tongue is used in the articulation of sounds, particularly in human speech.
The main anterior (front) portion of the tongue lies horizontally in the floor of the mouth; the back is curved round vertically and forms the anterior wall of part of the pharynx. The root of the tongue is embedded in the oral diaphragm; it is attached by various muscles to the hyoid bone and mandible, and to the soft palate by the arches of the latter.
On the dorsum, or upper surface, of the tongue is a large number of tiny projections known as papillae. At the front of the tongue these papillae are quite small. Some of them are narrow and high and called filiform papillae. Others are wider and only a little raised from the surface; these are called fungiform papillae. Farther back, arranged in the form of a V pointing towards the throat, are 9 to 14 much larger papillae. These are the vallate or circumvallate papillae, and are so-called on account of the ridge of tissue which runs like a wall around the edge of each one. Also on the dorsum are the taste buds – receptors that are sensitive to certain chemicals. Each taste bud is a tiny flask containing about half a dozen sensory cells. As with the sense of smell, substances must be in solution before they can be tasted.
The tip of the tongue rests against the back of the upper teeth and the undersurface is attached to the floor of the mouth by the frenulum.
The organ is mainly muscular, with right and left halves separated by a
fibrous partition called the median groove or median
sulcus; it has a mucus covering specialized for the sensation of
Muscles of the tongue
The muscles of the tongue fall into two groups. The extrinsic muscles are those which extend out of the tongue and are attached to nearby structures such as the hyoid bone and the mandible. These move the tongue bodily in the mouth.
The intrinsic muscles are wholly within the tongue. Their function is to alert the shape of the tongue. The fibers of the intrinsic muscles are arranged to run both across and along the tongue.
Functions of the tongue
The tongue has three main functions. First, it carries on its surface the taste buds which send information to the brain about the nature of the food being eaten. It seems likely that the sensation of taste is not merely to make eating a pleasure, but also to act as a protective mechanism designed to cause the rejection of noxious (harmful) foods.
Secondly, the tongue plays an important part in the process of digestion. It enables the food to be moved about the mouth and to be placed in a position where it can most effectively be ground down by the molars. When the contents of the mouth are ready to be swallowed, the tongue forms them into a ball, or bolus, which is moved toward the pharynx at the beginning of swallowing.
Finally, the tongue is concerned in speech. By assuming different positions in the mouth it alters the shape of the air passage through which pass the sounds made by the vocal cords. For example, if in the middle of saying "a ... a ...ah" the tip of the tongue is placed behind the upper teeth the sound immediately changes to "l".
The sensation of taste
In the epithelium which lines the vallate and fungiform papillae are the organs of taste, or taste buds. Each taste bud is like a minute flask with its open neck towards the cavity of the mouth. When we eat, some of the soluble elements of the food come into contact with the taste buds and reach the gustatory cells inside. These cells send impulses which are picked up by the nerve filaments in the base of the bud and transmitted to the brain.