Nervous supply of the geniohyoideus muscle is caused by the hypoglossal nerve. Accordingly, hypoglossal paralysis impairs the function of the muscle and causes a dysphagia that can occur in many neurological, muscular and other disorders.
One of the suprahyoid muscles in the human jaw region is the geniohyoideus muscle, also known as the chin-tongue leg muscle. In addition to the geniohyoideus, the group of suprahyoid muscles includes the digastric muscle, the mylohyoid muscle, and the stylohyoid muscle.
When swallowing and opening the jaw, these four muscles work together. The chin-tongue muscle is one of the skeletal muscles that are deliberately influenced. In addition, he is involved in various reflexes, such as automated swallowing and breaking. The embryo in the brain stem responds to potentially toxic substances and can trigger the emptying process. It coordinates the interaction of different nerves, muscles and glands.
The position of the geniohyoideus muscle is a feature that distinguishes the modern man (Homo sapiens) from the Neanderthal man: the latter had a horizontal chin-tongue muscle, while the geniohyoideus muscle is slightly oblique in Homo sapiens. This difference may affect the ability to articulate.
The geniohyoideus muscle originates from the spina mentalis, which forms a protrusion in the lower jawbone (os mandibulare) and can be found there on the inner surface (Facies interna). The attachment of the muscle is located on the hyoid bone (Os hyoideum).
In fine construction, the geniohyoideus muscle consists of striated muscle tissue, whose name goes back to the well-recognizable fiber structure. The individual elongated muscle fibers are each surrounded by a layer of connective tissue; inside are the threadlike myofibrils. Around them, the sarcoplasmic reticulum, which corresponds to the endoplasmic reticulum of other cells, is wound. The myofibrils can be divided into transverse sections, which are known as sarcomeres. One Z-disk delimits the sarcomere on both sides and serves as a support for tiny filaments.
According to the zipper principle, filaments of actin and tropomyosin on the one hand and myosin on the other hand are arranged alternately so that they can interlock when contraction of the muscle occurs. The geniohyoid muscle receives such neuronal signals via the hyoglossal nerve, which is connected to the spinal cord via the spinal segment C1 and also innervates the other suprahyoid muscles.
The function of the geniohyoideus muscle is to support jaw opening and swallowing, pulling the tongue forward. In addition, it participates in sideways movement of the jaw and, together with the other suprahyoid muscles, forms the musculature of the floor of the mouth. Motor fibers of the hypoglossal nerve transmit signals to the geniohyoideus muscle by releasing neurotransmitters at the juncture between the nerve fiber and the muscle cell.
These messengers reversibly attach to receptors located on the outside of the muscle cell membrane. An activated receptor opens ion channels through which charged particles flow into the cell and create an electrical endplate potential in the muscle. This spreads through the tissue of the geniohyoideus muscle and stimulates the sarcoplasmic reticulum to release calcium ions.
The ions bind to the actin / tropomyosin filaments of the fine myofibrils, which are bundled in the muscle fiber, and thus change their spatial structure. As a result, the myosin filaments with their "heads" on actin / tropomyosin strand stop. The myosin filaments thus move further between the complementary fibers and thereby actively shorten the sarcomere and ultimately the entire muscle. The contraction of the geniohyoideus muscle in turn pulls the tongue forward.
A lesion on the hypoglossal nerve may impair the function of the geniohyoid muscle if the innervating fibers no longer transmit nerve signals to the muscle. Hypoglossal paralysis typically affects not only the geniohyoid muscle but also the other tongue muscles.
Often, the nerve suffers damage in only one side of the face, resulting in a half-sided paralysis of the tongue. On a functional level, this paralysis often causes dysphagia and motor problems in speech. The tongue position often deviates from their normal attitude in the mouth. Persistent hypoglossal paralysis gradually leads to the atrophy of the affected muscles, resulting in a well-recognizable asymmetry, which becomes particularly visible when the tongue sticks out.
Hypoglossal palsy may be caused by a variety of causes, including stroke or cerebral infarction. In Germany 160-240 of 100, 000 people annually suffer from ischemic stroke, which is the most common type of brain infarction and is based on the supply of blood to the brain. The symptoms may vary depending on the affected area. Hypoglossal palsy can also be permanent damage if the nerve tissue is permanently damaged.
In particular, in the advanced course of Alzheimer's disease, swallowing disorders may also appear. The neurodegenerative disease is initially manifested in short-term memory disorders and leads to increasing symptoms such as agnosia, apraxia, speech and language disorders, apathy and ultimately bed-rest and numerous motor disorders. Neuromuscular disorders are, besides malformations and neoplasms, other possible causes of dysphagia that involve the geniohyoid muscle and other muscles. Immediate injury to the geniohyoideus muscle is possible during implant placement and other facial injuries and fractures.Tags: