The tongue is able to move in nearly every direction, expand, compress and display a fine degree of articulation. Such muscular control allows us to manipulate our food and speak. The organ's ability to transform into a variety of shapes comes from its composition of skeletal muscle interspersed with fat.
The tongue and its muscles are laterally symmetrical: a median septum divides the organ into two halves. The tongue is made up of two types of muscles: extrinsic and intrinsic. Extrinsic muscles originate from elsewhere in the body and attach to the tongue. They connect with surrounding bones and help the organ move up and down, from side to side and in and out. The tongue's extrinsic muscles all end in "glossus," which, unsurprisingly, means "tongue." The genioglossus depresses the tongue and thrusts it out. The styloglossus raises and withdraws the tongue. The palatoglossus raises its back. And, the hyoglossus lowers the tongue's sides.
Despite the tongue's fine degree of articulation, the extrinsic muscles also keep it firmly lashed in place. The muscles connect to the mandible, or jawbone, the hyoid bone, a U-shaped structure that supports the tongue, and the styloid processes of the temporal lobes. The styloid processes suspend the hyoid bone with muscles and ligaments, making it the only bone that doesn't come into contact with another.
Unlike extrinsic muscles, intrinsic muscles originate within the tongue. They allow it to expand and contract, altering its shape and size. The tongue's intrinsic muscles, which include the longitudinalis superior, longitudinalis inferior, transversus linguae and verticalis linguae, are especially important for speech and deglutition, or swallowing food.
Mucous membrane covers the tongue's mass of muscles and fat. The double-layered membrane helps block microbes and pathogens from entering the digestive system and other body cavities that come into contact with the outside. The epithelial layer of the mucous membrane secretes mucus that helps moisten the mouth and food.
The tongue is also an important organ for the perception of taste. In the next section, we'll learn about the tongue's role in taste.