The tongue is a muscular organ made up of arbitrary striated fibers. It can change shape and position, which ensures the processes of chewing food and speech. Its surface is mottled with nerve endings, so the tongue is the organ of touch and is more sensitive than the fingers. Language can be attributed to the sensory organs, namely taste. Unlike touch, only language is responsible for taste in the human body.
Language structure
The tongue is divided into the body, the tip, that is, the front-upper part, and the root located at its base and attached to the lower jaw, as well as the hyoid bone.
In a passive state, the language resembles a shovel in its form. It fills most of the mouth. The tip of the tongue touches the inside of the teeth.
The main part of this organ consists of muscles with ligaments. The tongue is covered with a mucous membrane, is penetrated by vessels, lymphatic ducts and nerves, it has many receptors, salivary glands. At the base of the tongue is the lingual tonsil. With an open mouth, it is not visible. It has an important immune function.
Tongue muscles
To better understand how the tongue is innervated, first you need to understand the structure of its muscles. Two groups stand out among them.
Skeletal muscles attach to the bones and end in the thickness of the tongue. Contraction of these muscles controls the position of the organ.
The awl-lingual muscle, as the name suggests, is attached to the styloid process and the awl-mandibular ligament, descends lower along the lower lateral part of the tongue. Her job is to move the tongue up and back. The chin-muscle is attached to the chin. Provides protruding tongue out. The hyoid-lingual muscle is attached to the hyoid bone, is sent to the lateral part of the tongue. This muscle moves the tongue down and back; in parallel, it lowers the epiglottis, which closes the larynx while eating.
Own muscles at both ends are embedded in its tissue and are not attached to the bones. They transform the form of language.
Among them, one can note the upper longitudinal muscle, raising the tip of the tongue, the lower longitudinal muscle shortening the tongue, the transverse muscle of the tongue, narrowing the tongue and making it more convex, and the vertical muscle of the tongue, which flattenes the tongue and makes it wider.
Language motor innervation
Tongue innervation is provided by 5 out of 12 cranial nerves. The hyoid nerve (XII pair) is responsible for the motor innervation of the tongue. Its motor path has two links. Its central neuron can be found in the cerebral cortex, in the lower third of the precentral gyrus - as well as for other motor nerves that innervate the organs of articulation. In this gyrus, the motor pyramidal path begins, which ends in the spinal cord, if we are talking about the innervation of the muscles of the limbs and trunk, or in the nuclei of the cranial nerves, if the muscles of the head and neck are innervated. This path is called pyramidal thanks to the pyramidal cells. This form has neurons in the cortex that control movements. The outline of the human body on this gyrus appears as if inverted, so neurons in its lower third are responsible for the work of the tongue.
The next neuron is in the nucleus of the medulla oblongata. The nerve innervates the own muscles of the tongue, and besides them, those of the skeletal ones that move the tongue forward and up, down and back. For example, the chin-muscle. When the peripheral nucleus of this nerve is affected, it pushes the tongue to the paralyzed side.
However, not all muscles of the tongue are controlled by the hyoid nerve. The vagus nerve (X pair) is also involved in the innervation of the tongue. It is called wandering, since it permeates a huge number of organs, and its branches can be found almost everywhere. Also, this nerve provides the parasympathetic nervous system. Skeletal muscle is innervated by its 2 branches: the superior laryngeal nerve controls the submental hyoid muscle, and the lower laryngeal nerve controls the sublingual-lingual and styloid muscles. The central neuron of its path can also be found in the lower third of the precentral gyrus. And peripheral - also in the medulla oblongata, where the nucleus of the vagus nerve is located.
Sensitive innervation
The central neurons of the sensory nerves are located in different areas of the cortex depending on their specialization. General sensitivity is presented in the somatosensory zone - in the postcentral gyrus of the parietal lobe, also in the lower third. And the taste is presented in the taste crust just below.
The innervation of the tongue in the anterior 2/3 is carried out by the lingual nerve. It is a branch of the mandibular nerve (III pair). It provides general sensitivity - touch, sensation of pain, heat and cold in the front of the tongue, as well as the mucous membrane of the bottom of the oral cavity, the front of the lower gum, palatine arches and tonsils. Not only the general, but also the taste sensitivity of the posterior third of the tongue is the glossopharyngeal nerve (IX pair).
A taste sensation from the anterior 2/3 of the tongue is transmitted by a drum string - a branch of the facial nerve (VII pair). She also innervates the salivary glands. Chains from sensitive neurons are more complicated than from motor ones. Typically, the circuit includes 3 neurons. The first one is located in the nucleus of the corresponding nerve, the next in the thalamus, the central one in the somatosensory and gustatory cortex. This applies to all of the above sensory nerves.
Blood circulation in the tongue
Blood enters the tongue through the lingual arteries, which are a branch of the external carotid artery. The network formed by these branches and includes loops, and provides blood circulation to the tongue.
Lingual veins (tributaries of the internal jugular vein) provide venous outflow.
The structure and features of the mucous membrane
The surface of the tongue is covered with a mucous membrane, where there is no submucosal layer. Because of this, unlike the mucous membranes of other organs, it does not have folds. The mucous membrane of the tongue is lined with stratified squamous epithelium. The back of the tongue and its edges have a rough surface, and the lower surface is smooth due to the absence of papillae.
The mucous membrane on it forms a bridle. It is especially pronounced in some children and may make it difficult to master articulation. With insufficient mobility of the tongue and a shortened and thickened bridle, connective tissue fibers can be distinguished in it. A short bridle that cannot be stretched with the help of special exercises can serve as an indication for surgery.
Taste papillae
There are 4 types of taste buds in the mucous membrane of the tongue.
The filiform and conical papillae of the tongue are the most numerous, they cover the entire front part from above. They are not taste buds, but serve to touch, perceive pain and temperature. In cats, such papillae are especially developed and resemble tiny hooks. This makes their tongue rough, like sandpaper, and allows them to strip pieces of meat from bones. You can notice this feature in a domestic cat.
Mushroom papillae of the tongue really resemble mushroom caps in their shape. They are recognized as taste buds. In most of them are the so-called taste bulbs, consisting of supporting cells and taste receptors proper. When a substance dissolved in saliva enters the chemoreceptor through the pore, it transmits a signal to the brain. If there are a lot of such signals, a person feels the taste. Mushroom papillae specialize in perceiving a sweet taste.
Grooved papillae are the largest. Their name is associated with their shape - they are as if surrounded by a moat. It is assumed that they perceive a bitter taste.
Leaf-shaped determine sour taste. Their accumulation can be found at the edges of the tongue.
Salivary glands
Among the salivary glands of the tongue, serous, mucous and mixed are distinguished. Serous are located next to the grooved and leaf-shaped papillae in the tissues of the tongue. Mucous glands are located in the root of the tongue and along its edges. The excretory ducts of these glands open into the crypts of the lingual tonsil. Mixed glands are at the tip of the tongue. Their ducts go to its lower surface.
Saliva performs many functions. For example, it helps to start digesting food already in the oral cavity thanks to enzymes such as amylase (breaks down starch) and others. Saliva also has a bactericidal function. A substance such as lysozyme successfully fights with many pathogens. Despite this, there is always a lot of bacteria in the saliva itself. Each person has a different bacterial composition of saliva .
Language development in the prenatal period and childhood
In intrauterine development, the muscles of the tongue are formed from the mesenchyme, and its mucosa is formed from the ectoderm. First, 3 rudiments of the tongue are formed. When they merge, two noticeable grooves remain in the tongue - the median and borderline. Taste buds are formed in the fetus at 6-7 months.
The age-related features of the language are that in newborns it is quite wide, shortened and inactive. It occupies the entire oral cavity of the child.
When the baby’s mouth is closed, the tongue protrudes beyond the edges of the gums. The vestibule of the mouth is still small. The tongue protrudes into it between the gums, usually without teeth. Papillae of the tongue are already markedly pronounced. The lingual tonsil is underdeveloped.
Language plays an important role in the life of the child - it is involved in sucking the mother’s breast. In the future, the language helps to make sounds and takes part in babble and babble.
Since the language has the most nerve endings, children use it to explore the world through touch. That is why they stick things in their mouths.
The development of the muscles of the tongue and the coordination of its nerves and the motor parts of the brain that control its movements are very important for the formation of speech, especially pronunciation. In Russian, many sounds require the participation of the tip of the language, its subtle and differentiated movements. In a small child, the tip of the tongue is not expressed, and in some children its mobility and sensitivity are delayed in development. One of the first in children to appear rear-lingual sounds that occur when the root closes with the sky. These sounds can be heard already in the walk of the baby. The fact is that the child is lying on his back and his tongue is slightly sunken back.
The work of the muscles of the tongue in children is not yet very differentiated. It is difficult for them to control his voluntary movements and, on command, to touch him with the tip of his teeth or cheeks.
Tongue redness
The tongue usually has a pink color, because blood vessels shine through its mucosa. The red tongue speaks of violations in the functioning of internal organs or about diseases of the tongue itself, for example, its inflammation - glossitis. Usually in this case, redness is accompanied by soreness, swelling. Gust sensitivity may even decrease or disappear. The causes of glossitis are bad habits, problems with the digestive system, various injuries of the tongue with teeth or dentures, burns with excessively hot food and drinks. With this disease, it is usually recommended to wipe the tongue with antiseptics.
Of course, the effect of redness can produce food colors red, caught on the tongue with food. Also, a red tongue happens when the temperature rises, when redness of the face and mucous membranes occurs.
Red plaque on the tongue may be present with lesions of the central nervous system, in some cases, the digestive and respiratory organs. Therefore, in the case of red plaque, you must always consult a doctor, since it is impossible to make a diagnosis on your own.