The tongue is a muscular organ composed of arbitrary striated fibers. It can change shape and position, which provides the processes of chewing food and speech. Its surface is dotted with nerve endings, so the tongue is an organ of touch and is more sensitive than the fingers. The tongue can be attributed to the sense organs, namely taste. Unlike touch, only the tongue is responsible for taste in the human body.
Structure of language
The tongue is divided into the body, the tip, that is, the anterior-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 tongue resembles a shovel in its shape. It fills most of the mouth. The tip of the tongue touches the inner surface of the teeth. The main part of this organ consists of muscles with ligaments. The tongue is covered with a mucous membrane, permeated with vessels, lymphatic ducts and nerves, it has many receptors, salivary glands. At the base of the tongue is the lingual tonsil. When the mouth is open, it is not visible. It has an important immune function.
Muscles of the tongue
To better understand how the tongue is innervated, first you need to understandthe structure of his muscles. Two groups stand out among them.
Skeletal muscles are attached to the bones and end in the thickness of the tongue. The contraction of these muscles controls the position of the organ.
The stylo-lingual muscle, as the name implies, is attached to the styloid process and the styloid-mandibular ligament, descends lower along the lower-lateral part of the tongue. Her job is to move the tongue up and back. The genioglossus muscle is attached to the chin bone. Provides protrusion of the tongue out. The hyoid-lingual muscle is attached to the hyoid bone, directed 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 during meals.
Own muscles are both ends embedded in his tissue and not attached to the bones. They transform the shape of the tongue.
These include the superior longitudinal muscle, which raises the tip of the tongue, the inferior longitudinal muscle, which shortens the tongue, the transverse tongue muscle, which narrows the tongue and makes it more prominent, and the vertical tongue muscle, which flattens the tongue and makes it wider.
Motor innervation of the tongue
Innervation of the tongue is provided by 5 out of 12 cranial nerves. The hypoglossal nerve (XII pair) is responsible for the motor innervation of the tongue. His 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 innervating the organs of articulation. In this gyrus, the motor pyramidal path begins, whichends 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 due to the pyramidal cells. This is the shape of the neurons in the cortex that control movement. The scheme of the human body on this gyrus appears as if upside down, so the neurons in its lower third are responsible for the work of the language.
The next neuron is in the nucleus of the medulla oblongata. The nerve innervates its own muscles of the tongue, and in addition to them, those of the skeletal muscles that move the tongue forward and up, down and back. For example, the genio-lingual 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 hypoglossal nerve. The vagus nerve (X pair) is also involved in the innervation of the tongue. It is called wandering, because it penetrates a huge number of organs, and its branches can be found almost everywhere. Also, this nerve provides the work of the parasympathetic nervous system. And the innervation of the skeletal muscles is carried out by 2 of its branches: the superior laryngeal nerve controls the geniohyoid muscle, and the inferior laryngeal nerve controls the hyoid-lingual and styloglossus muscles. The central neuron of its pathway can also be found in the lower third of the precentral gyrus. And the peripheral one is also in the medulla oblongata, where the nucleus of the vagus nerve is located.
Sensitive innervation
The central neurons of 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 bar just below.
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 anterior part of the tongue, as well as the mucosa of the floor of the mouth, anterior part of the lower gums, palatine arches and tonsils. The glossopharyngeal nerve (IX pair) is responsible not only for general, but also for taste sensitivity of the posterior third of the tongue.
And taste sensations from the anterior 2/3 of the tongue are transmitted by the drum string - a branch of the facial nerve (VII pair). It also innervates the salivary glands. Circuits of sensory neurons are more complex than those of motor neurons. Usually the circuit includes 3 neurons. The first of them is located in the nucleus of the corresponding nerve, the next one is in the thalamus, the central one is in the somatosensory and gustatory cortex. This applies to all of the above sensory nerves.
Circulation in the tongue
Blood enters the tongue through the lingual arteries, which are branches of the external carotid artery. The network formed by these branches and including loops provides blood supply to the tongue.
The lingual veins (tributaries of the internal jugular vein) provide venous drainage.
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 mucousother organs, it has no 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 frenulum. It is especially pronounced in some children and can make it difficult to master articulation. With insufficient mobility of the tongue and a shortened and thickened frenulum, connective tissue fibers can be distinguished in it. A short frenulum that cannot be stretched with special exercises may be an indication for surgery.
Taste buds
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 anterior part of the tongue from above. They are not taste buds, but serve the sense of touch, the perception of 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 scrape bits of meat off the bones. You can notice this feature in a domestic cat.
The fungiform papillae of the tongue really resemble mushroom caps in their shape. They are recognized as taste buds. In most of them there are so-called taste buds, consisting of supporting cells and the actual taste receptors. When a substance dissolved in saliva enters the chemoreceptor through the pore, it transmits a signal to the brain. If such signals are sufficienta lot, a person feels the taste. Fungiform papillae are specialized for sweet taste.
Grooved papillae are the largest. Their name is associated with their shape - they are, as it were, surrounded by a moat. They are supposed to perceive the bitter taste.
Leaf-shaped determine the sour taste. Their accumulation can be found along the edges of the tongue.
Salivary glands
Among the salivary glands of the tongue are serous, mucous and mixed. Serous are located next to the grooved and foliate papillae in the tissues of the tongue. The mucous glands are located at 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 located at the tip of the tongue. Their ducts exit to its lower surface.
Saliva performs many functions. For example, it helps to start the digestion of food already in the oral cavity due to enzymes such as amylase (breaks down starch), etc. Saliva also performs a bactericidal function. A substance such as lysozyme successfully fights many infectious agents. Despite this, saliva itself is always full of bacteria. Each person has a different bacterial composition of saliva.
Language development in utero and childhood
In prenatal 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 are fused, two noticeable furrows remain in the tongue - median and borderline. Taste buds are formed in the fetus at 6-7 months.
Age features of the languagelie in the fact that in newborns it is quite wide, shortened and inactive. It occupies the entire cavity of the baby's mouth. 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 devoid of teeth. The papillae of the tongue are already markedly expressed. The lingual tonsil is underdeveloped.
Language plays an important role in the life of a child - it is involved in sucking the mother's breast. In the future, the tongue helps to make sounds and takes part in cooing and babbling.
Because the tongue has the most nerve endings, children use it to explore the world with their sense of touch. That's why they put things in their mouths.
The development of the muscles of the tongue and coordination, its nerves and the motor parts of the brain that control its movements, is very important for the development of speech, especially pronunciation. In Russian, many sounds require the participation of the tip of the tongue, its subtle and differentiated movements. In a small child, the tip of the tongue is not pronounced, and in some children its mobility and sensitivity are delayed in development. One of the first to appear in children are posterior lingual sounds that occur when the root closes with the sky. These sounds can be heard already in the cooing of a baby. The fact is that the child lies on his back and his tongue slightly sinks 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, touch him with the tip of his teeth or cheeks.
Redden tongue
Language usually haspink color, because vessels are visible through its mucosa. The red tongue speaks of disturbances in the functioning of the internal organs or of diseases of the tongue itself, for example, its inflammation - glossitis. Usually in this case, redness is accompanied by soreness, swelling. There may even be a decrease or loss of taste sensitivity. 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. In this disease, it is usually recommended to wipe the tongue with antiseptics.
Of course, the effect of redness can be produced by red food dyes that have fallen on the tongue with food. Also, a red tongue occurs with an increase in temperature, 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, it is imperative to consult a doctor, since it is impossible to make a diagnosis on your own.
