The transversus linguae muscle is an internal tongue muscle that stretches and curves the tongue. In this way, it contributes to chewing, speaking, and swallowing. Failure of the transversus linguae muscle may be due to hypoglossal palsy, for example, as a result of a stroke.
What is the transversus linguae muscle?
When speaking, swallowing, chewing, and yawning, the tongue is indispensable. Its movements are based on the interaction of many different muscles, which include the internal tongue muscles. One of them is the transversus linguae muscle. It represents a small, striated skeletal muscle and participates mainly in movements in the longitudinal direction of the tongue – for example, when sticking it out. The internal tongue musculature also includes the musculus longitudinalis inferior and the musculus longitudinalis superior, both of which extend longitudinally through the tongue. The Musculus verticalis linguae, which extends between the tongue aponeurosis (aponeurosis linguae) and the back of the tongue, is also part of the inner tongue musculature. The names are derived from the respective anatomical location of a muscle. Within the tongue, all muscles are interwoven in three dimensions. In addition to the internal tongue muscles, which are intrinsic muscles of the organ, humans also possess external tongue muscles, which are located outside the organ.
Anatomy and structure
The transversus linguae muscle runs across the tongue. Its origin is at the lingual septum (septum linguae), which lies in the middle of the tongue and often forms a median fold when stretched out. The transversus linguae muscle extends from the septum to the lateral border of the tongue. Unlike other striated muscles, it does not have orderly bundles of muscle fibers, each of which combines several muscle fibers. Instead, its fibers extend through the tongue tissue and are intertwined with other fibers. Through each muscle fiber, corresponding to a muscle cell with multiple nuclei, are longitudinally aligned myofibrils. These filaments are divided into sections called sarcomeres, which are responsible for the muscle’s striated structure. Protein structures create different translucent parts that appear as light and dark bands under the microscope. These bands are the contractile units of the muscle: they can push into each other and thus shorten. The transversus linguae muscle receives the signal to do this from the twelfth cranial nerve (hypoglossal nerve), which anatomists also call the tongue-gullet nerve because of its course.
Function and Tasks
The transversus linguae muscle is active in various tongue movements: in extending and protruding the tongue, and in transverse arching. However, because the transversus linguae muscle is intertwined with the other internal tongue muscles, it is not the only one responsible for the movements. During the swallowing process, the transversus linguae muscle is primarily involved in the oral preparation phase and the oral transport phase. These two sections represent the first two steps in the swallowing act. In the oral preparation phase, the mouth grinds food between the teeth. The tongue movements perform two functions in this process: First, they ensure that the tongue does not accidentally get between the teeth, and second, they repeatedly push the food pulp from the center of the mouth to the sides. This is also where the transverse curvature of the tongue comes into play, for which the transversus linguae muscle is responsible. If the food is sufficiently crushed or the person swallows only liquid, the oral transport phase then follows. Here, the tongue muscles first press the tongue against the palate, tilting it backward so that the food can already slide backward toward the pharynx. In addition, the inner tongue muscles perform a wave motion that supports the transport. In the pharynx, touching the food triggers the swallowing reflex and the pharyngeal transport phase begins: After the nose and larynx or trachea have closed, the muscles push through the pharynx into the esophagus. There, the esophageal transport phase begins, ending when the food or liquid enters the stomach. The transversus linguae muscle is also necessary for speech. The tongue contributes to the articulation of sounds and forms, for example, consonants such as “L” and “N”.
Diseases
In hypoglossal nerve palsy, the nerve supply to the transversus linguae muscle is completely or partially interrupted. As a result, discomfort is seen in swallowing, chewing, and speaking. When sticking out, the tongue may hang down on one side or give an overall slack impression. Often, only one half of the tongue is affected by hypoglossal palsy. If the loss of the twelfth cranial nerve is irreversible or persists for a long time, the body gradually breaks down the affected muscles. In this case, medicine refers to atrophy, or tissue atrophy. Hypoglossal palsy can be due to damage in the periphery, but it can also be caused by diseases of the central nervous system. It often occurs in the context of an ischemic stroke. Poor blood flow to the brain triggers cerebral infarction and causes neurological symptoms such as confusion, speech disorders, hemiplegia, cognitive impairment, visual disturbances or motor difficulties. Symptoms may vary in individual cases, however, because they depend on the location and extent of the affected brain regions. Hypoglossal palsy affects not only the transversus linguae muscle but also the other tongue muscles. Other possible causes of hypoglossal palsy include infection, hemorrhage, traumatic brain injury, tumors, and other diseases. Less commonly, the hypoglossal nerve sustains damage during surgical procedures in the head and neck region.
