How does the tongue work?
“Having something on the tip of your tongue”, “biting your tongue” or speaking “tongue-in-cheek” – this set of muscles covered with mucous membrane appears in so many idioms for good reason: the tongue is a true all-rounder. It is not only very movable, which allows us to speak, suck or swallow in a coordinated way. It is also a sensory organ responsible for tasting and the most sensitive place for our sense of touch. In addition, the tongue contains many cells of the body’s defense system, and even plays a major role in body language.
What is the tongue?
The tongue is an extremely movable set of muscles, which is well-supplied with blood and has many nerves. The tongue muscles have an oblong shape and are covered with a dense layer of connective tissue. Above this layer, a special kind of mucous membrane makes up the surface of the tongue.
Back, tip, root – the sections of the tongue
The tongue can be divided into different sections:
- Tip and sides of the tongue: These are parts of the movable section of the tongue. These areas are very movable and can perform complex movements.
- Back of the tongue: The upper surface of the tongue is called the back of the tongue. It has many sensory cells for our senses of taste and touch.
- Root of the tongue: The root of the tongue cannot move freely and is connected to the floor of the mouth. It is also called base of the tongue and cannot be seen by the naked eye.
Rough or velvety: the surface of the tongue
If you look at your tongue in the mirror, you usually see a slightly white, matt surface. The back of the tongue is curved outwards slightly, and in the middle it falls towards the groove that divides the tongue in half lengthwise.
The rough surface of the tongue is due to a special feature of the mucous membrane: the papillae, which appear as many small bumps on the tongue. They are formed by cells or groups of cells of the layers underneath bulging. These papillae have different jobs to do:
These papillae anchor the mucous membrane firmly to the tongue. They also sense touch so that we can feel the form and texture of food in our mouth.
The most important task for taste papillae is making the surface of the tongue much bigger. This allows the greatest number of sensory cells embedded there to have contact with food particles for tasting.
Saliva and food residue can get stuck in the grooves between the papillae, especially on the last third of the tongue. This can favor the development of putrefactive (rot-causing) bacteria. Then a whitish film covers the tongue, which also causes bad breath. These bacteria mainly live on remains of protein-rich food like fish, cheese or milk.
Underneath the tongue: always ready for absorption
If you stick out the tip of your tongue and move it upwards you can see the shiny surface underneath: The most noticeable part of it is the lingual frenulum and a vein on either side of it, which can be seen as bluish strings underneath the mucous membrane. The two salivary glands of the lower jaw (submandibular glands) have their ducts where the tongue meets the floor of the mouth.
The mucous membrane of the tongue can absorb some substances – for example medications that are to act quickly. The tablet, fluid or spray is put underneath the tongue, but is not meant to be swallowed. This is called sublingual administration (from the Latin: lingua, meaning “tongue” or “language”). One example is nitroglycerin spray used in sudden chest pain caused by reduced blood flow through the coronary arteries. This spray acts very quickly because it directly enters the bloodstream. If it was swallowed it would have to pass the stomach and bowel to reach the liver. There it would be only partly broken down before being made suitable for use by the body.
Unique to the body: three-dimensional muscle fibers
The tongue has a great ability to move in all directions. The reason for this is the way the muscle fibers are arranged, which is unique in our body. They run in all three directions: from front to back, from the sides to the middle and from top to bottom. This allows the tongue to make the following movements:
- Extending and contracting: The tongue is the only muscle in our body that can actively contract and extend. When the vertical and horizontal fibers contract at the same time, the tongue becomes narrower and longer: we can stick our tongue out.
- Raising and lowering
- Bending backwards
- Advancing and retracting
- Rounding or hollowing
- Making grooves
- Changing its position: Additional muscles can change the position of the tongue: They pull into the tongue from the front (from the lower jaw), from below and behind (from the hyoid bone) and from above and behind (from the base of the skull).
The tongue’s jobs
Eating and drinking
Being extremely movable, the tongue’s main job is helping us eat: It enables us to suck, turns solid food into a mash that can be swallowed (bolus) and starts the act of swallowing. The tongue can also differentiate many tastes and flavors, which helps us tell whether the food is good for us.
The tongue is vitally important, particularly for babies when breastfeeding. It works like a piston, with the cavity of the mouth being the cylinder: When then tongue moves backward in the closed mouth it produces low pressure, which sucks in fluid for drinking.
Chewing, grinding, pressing, salivating
When we chew, the tongue and the cheeks work together to constantly move the food between the teeth so that it can be chewed. The tongue presses the crushed food against the palate and moves this bolus, which is then ready to be swallowed, to the throat. The movements of the tongue also massage small glands directly underneath it and squeeze out saliva. This starts pre-digestion of the food, and the bolus can glide down the esophagus more easily.
The tongue presses the bolus into the throat, which starts the process of swallowing.
The tongue’s mucous membrane contains many taste receptors to test the things we eat and drink. They are found in the taste buds where they are arranged like orange sections around a fluid-filled funnel. This is where the chemical substances responsible for taste are washed up and recognized by the sensory cells. The sense of taste used to be vital to our survival because it was the only way to test food and tell the difference between good and poisonous or bad food. Many taste stimuli also trigger increased production of saliva and stomach acid to start digestion.
The tip of the tongue is the part of the body that is most sensitive to touch. This fine sensitivity to touch has two main tasks: On the one hand, it tests the mechanical characteristics of the food. This high level of sensitivity is the reason why small stones, bone splinters or fish bones feel much larger than they really are. This magnifying effect of the tongue protects us. On the other hand, the tongue searches the entire mouth for remaining rests of food after the first bite.
Humans also use the tongue’s movability for speaking. Only when tongue, lips and teeth work together do sounds from the throat turn into understandable letters and words. The tongue is extremely agile and quick: It can produce more than 90 words per minute, using more than 20 different movements. The tongue is essential for pronouncing the consonants “t”, “d”, “l” or the rolling “r”. When pronouncing the letter “k” the tongue is slightly narrowed at the back. And when we say “s”, the tip of the tongue moves backwards. If the tip of the tongue remains between the teeth, we hear a typical lisp.
The fact that the tongue is essential for speaking can also be seen in the ability of parrots to imitate human language: Although they only have a very simple organ of speech with fewer muscle groups than humans, they have an extraordinarily thick tongue. This helps them to produce the sounds of human language. They can touch the tip of their tongue to certain points of articulation in their mouth to imitate human words in a deceptively similar way.
All the defense cells of the tongue are collectively called the lingual tonsil (tonsilla lingualis). It is found in the back of the mouth at the base of the tongue and is part of the lymphatic tonsillar ring. Together with the palatine tonsils and the adenoids, the lingual tonsil is responsible for defending the body against germs that can come in through the mouth.
If you would like to know more about how the sense of taste works, read on here.
Author: Institute for Quality and Efficiency in Health Care (IQWiG)
- January 23rd 2013 16:03
- December 19th 2011 15:43
- Show list
Schmidt RF, Lang F, Heckmann M. Physiologie des Menschen. Heidelberg: Springer Medizin Verlag. 2010.
Thews G, Mutschler E, Vaupel P. Anatomie, Physiologie, Pathophysiologie des Menschen. Stuttgart: Wissenschaftliche Verlagsgesellschaft. 1999.
Plattig KH. Spürnasen und Feinschmecker, die chemischen Sinne des Menschen. Berlin Heidelberg. Springer Verlag 1995.
Schäffler A, Schmidt S. Biologie, Anatomie, Physiologie. Stuttgart: Gustav Fischer Verlag. 1998.
Roche-Lexikon Medizin, 5th edition, accessed on September 14, 2011: [http://www.tk.de/rochelexikon/]