The longitudinalis inferior muscle is one of the internal tongue muscles. Its fibers run longitudinally through the tongue and cause various tongue movements. In hypoglossal palsy, the longitudinalis muscle fails along with other tongue muscles, usually causing discomfort during swallowing and speaking.
What is the inferior longitudinalis muscle?
The longitudinalis inferior muscle is located in the tongue, which is why anatomy includes it among the internal tongue muscles. Its structure is not clearly delineated from the other muscles in this group. Instead, the internal tongue muscles form a plexus that can be roughly divided into different layers according to the location and orientation of the fibers. The Musculus longitudinalis inferior embodies the lower longitudinal fibers of the tongue. The upper longitudinal fibers, on the other hand, correspond to the Musculus longitudinalis superior. The other two tongue muscles represent the Musculus transversus linguae and the Musculus verticalis linguae. In addition to the inner tongue musculature, humans also possess an outer tongue musculature. These are the hyoglossus, genioglossus, styloglossus, palatoglossus and chondroglossus muscles. All tongue muscles are composed of striated fibers and are part of the skeletal musculature.
Anatomy and structure
The origin of the inferior longitudinalis muscle is at the root of the tongue. This is also known as the radix linguae and is located at the posterior end of the tongue facing the pharynx. At the base, some fibers of the longitudinalis inferior muscle intermingle with fibers of the styloglossus muscle. This external tongue muscle spans between the hyoid bone (Os hyoideum) and the tongue. Individual fibers of the longitudinalis inferior muscle are also connected to the hyoid bone. The longitudinalis inferior muscle extends longitudinally through the tongue from the root of the tongue and attaches at the tip (apex linguae). There, its fibers meet the genioglossus muscle, which is the chin-tongue muscle that projects from the mandible into the tongue. As a striated skeletal muscle, the inferior longitudinalis muscle consists of segments (sarcomeres) that are repeated within each fiber. Protein filaments are arranged alternately within them. The filaments are structures of myosin and complexes of actin and tropomyosin. When the muscle tenses, these filaments push into each other, shortening the muscle fibers.
Function and tasks
The function of the inferior longitudinalis muscle is to raise the tip of the tongue. In addition, it is capable of shortening and arching the tongue. The Musculus longitudinalis inferior acts as an antagonist of the Musculus transversus linguae and the Musculus verticalis linguae. However, it usually acts in concert with the superior longitudinalis muscle because its fibers follow a similar course through the tongue and perform the same functions. The inferior longitudinalis muscle receives nerve signals from the hypoglossal nerve, also known as the tenth cranial nerve. Its nucleus is located in the central nervous system in the medulla oblongata. The hypoglossal nerve passes through the hypoglossal canal (Canalis nervi hypoglossi) from the skull into the neck. All tongue muscles except the palatoglossus muscle receive their commands to contract via the tenth cranial nerve. The nerve fibers represent the long extensions of individual nerve cells and carry information in the form of electrical impulses. Motor nerve tracts terminate at the muscle in a motor end plate, where the nerve signal passes from the neuronal fiber to the muscle. Together with the other internal and external tongue muscles, the inferior longitudinalis muscle controls the movements of the tongue. It assists chewing by repeatedly pushing food from the center of the mouth to the teeth. In addition, the tongue participates in swallowing and supports the articulation of sounds. The tongue plays a particularly important role in the formation of linguals (tongue sounds).
Diseases
Stroke can cause hypoglossal nerve failure if the circulatory disturbance in the brain affects the core area of the cranial nerve. The core of the hypoglossal nerve is located in the medulla oblongata: this is where the neurons responsible for motor control of the inferior longitudinalis muscle and most other tongue muscles are located.As a rule, a stroke leads to the unilateral loss of the hypoglossal nerve. Affected individuals often experience dysphagia (difficulty swallowing) and speech difficulties because hypoglossal nerve palsy restricts the functioning of the tongue. Symptomatically, the tongue shifts to one side. While the tongue is in the mouth, it deviates to the side that is not disturbed by the stroke. However, when the patient sticks the tongue out, it leans toward the side that was damaged. In addition, a stroke often results in numerous other symptoms. These include sensory disturbances, confusion, dizziness, nausea, vomiting, visual disturbances, headaches, word-finding disorders, neglect, and difficulties with orientation, coordination, and/or walking. In addition, individual extremities, one side of the body, or the face may be paralyzed. Not all symptoms have to occur together and additional symptoms are also possible. When a stroke occurs, prompt treatment is needed to contain the damage to the brain caused by the circulatory disturbance. However, hypoglossal paralysis, and thus a failure of the tongue muscles, is not always related to a stroke. Other possible causes include tumors, inflammation, and dementia. Ulcers and inflammations do not have to occur in the brain, but can also occur later in the course of the hypoglossal nerve and impair its function. In addition, nerve lesions are possible in severe head injuries.
