While the tongue's muscles guide food between the teeth and shape it so that it's digestible, the peripheral sense organ is perhaps better known for its role in the perception of taste. The tongue not only detects gustatory (taste) sensations, but also helps sense the tactile, thermal and even painful stimuli that give food its flavor.
Most people mistake the bumpy structures that cover the tongue's surface for taste buds. These are actually papillae: goblet-shaped elevations that sometimes contain taste buds and help create friction between the tongue and food. Taste buds are smaller structures, tucked away in the folds between papillae. Every taste bud is made up of basal and supporting cells that help maintain about 50 gustatory receptor cells. These specialized receptors are stimulated by the chemical makeup of solutions. They respond to several primary tastes: sweet, salty, bitter, sour, umami (savory) and fat, which some scientists claim might be a sixth taste. When a stimulus activates a gustatory cell, the receptor will synapse with neurons and send an electrical impulse to the gustatory region of the cerebral cortex. The brain interprets the sensation as taste.
Each gustatory receptor cell has a long, spindlelike protrusion called a gustatory hair that comes into contact with the outside environment. The hair extends from a small opening, or taste pore, and mingles with molecules of food introduced by saliva. The saliva solution contains digestive enzymes that help break down foods chemically. Saliva is secreted by three major salivary glands -- the parotid, submandibular and sublingual glands -- as well as other small salivary glands contained within the tongue and mouth.
Aside from the tongue's ability to detect gustatory stimuli, it also perceives temperature and the complex tactile sensations that food scientists call mouth feel. The tongue, along with the rest of the mouth, helps determine a food's texture, oiliness, chewiness, viscosity and density.
In the next section, we'll learn about how the tongue functions in speech.