ABSTRACT
In humans, the tongue aids in creating negative pressure within the oral cavity that enables sucking, and it is an important accessory organ in chewing, swallowing and speech. The tongue consists of a mass of interwoven, striated muscles interspersed with glands and fat and covered with mucous membrane. The ability of the tongue to touch the lips and teeth aids swallowing and speech. The top surface, or dorsum, contains numerous projections of the mucous membrane called papillae. They contain taste buds sensitive to food flavours and serous glands that secrete some of the fluid in saliva. The base, or upper rear portion, of the tongue has no papillae, but aggregated lymphatic tissue (lingual tonsils) and serous and mucus-secreting glands are present. The inferior, or under surface leads from the tip of the tongue to the floor of the mouth; its mucous membrane is smooth and purple in colour from the many blood vessels present. The root, the remainder of the underside that lies on the floor of the mouth contains bundles of nerves, arteries, and muscles that branch to the other tongue regions. Nerves from the tongue receive chemical stimulation from food in solution which gives the sensation of taste. There are four fundamental taste sensations: salt and sweet, the receptors for which are primarily located at the tip of the tongue, bitter at the base, and acid or sour along the borders. The flavour of a food comes from the combination of taste, smell, touch, texture or consistency, and temperature sensations.
