The musculus stylohyoideus is a small skeletal muscle in the jaw area. It is part of the suprahyoid musculature and contributes to the swallowing and opening of the jaw. A dysphagia may also affect the stylohyoid muscle and lead to functional impairment.

What is the stylohyoid muscle?

The stylohyoid muscle is a striated muscle involved in opening the jaw and swallowing. It belongs to the group of suprahyoid muscles, which are also known as floor muscles or upper hyoid muscles and in addition to the musculus stylohyoid four other muscles include: the musculus digastricus, the geniohyoideus muscle and the mylohyoid muscle.

Both when swallowing and when opening the jaw, these muscles work together in a coordinated manner. The control is based on the Seventh Cranial Nerve, which as a facial nerve or facial nerve penetrates numerous tissue structures in the head with the help of numerous branches (Rami). Its fibers not only conduct motor and parasympathetic signals from the central nervous system to the innervated muscles, but also carry sensory and sensory nerve signals in the opposite direction.

Anatomy & Construction

The origin of the musculus stylohyoid lies on the temporal bone (os temporale), which belongs to the skull. Inside him are the inner ear and the middle ear. At the temporal bone, the stylohyoid muscle originates from the styloid process (styloid process), which represents an extension of this cranial bone.

The attachment of the stylohyoid muscle is located on the hyoid bone (Os hyoideum), where a tendon fixes the striated muscle to the bone and also attaches the tendon of the digastric muscle. The musculus digastricus is another suprahyoid muscle, which is also known as a biceps due to its shape. The stylohyoid ligament - a pair of ligaments - spans from the styloid to the hyoid bone, connecting the two bones together.

Like all striated skeletal muscles, the stylohyoid muscle consists of muscle fibers that correspond to the muscle cells. They have multiple cell nuclei because the conventional cell structure does not exist in them. Instead, there are several myofibrils inside a muscle fiber, which run longitudinally through the fiber and are surrounded by the sarcoplasmic reticulum. When the transverse sections of the myofibrils (sarcomeres) shorten as the actin / tropomyosin and myosin filaments within them contract, the muscle contracts as a whole causing a movement of the hyoid bone.

Function & Tasks

The stylohyoid muscle exerts both a static and a dynamic function. Together with other muscles and ligaments, he holds the hyoid bone (Os hyoideum), which otherwise has no direct connection to other bones. The hyoid bone is composed of the middle body and the lateral horns; the attachment of the stylohyoid muscle is distributed over the body and the large horn of the bone.

The dynamic function of the stylohyoid muscle is to aid swallowing and jaw opening, working with the other suprahyoid muscles. The order for contraction receives the musculus stylohyoid of the facial nerve. The electrical signal ends in the end button of the innervating nerve fibers, where it is accompanied by an influx of calcium ions. As a result, some bubbles that are in the end-button unite with the outer membrane and release the neurotransmitters they contain.

As a messenger, acetylcholine transiently binds to receptors in the membrane of a muscle cell, causing the influx of ions that create a new electrical potential: the endplate potential that passes through the sarcolemma and tubular T-tubules into the sarcoplasmic reticulum. Calcium ions from the sarcoplasmic reticulum penetrate into the interior of the myofibrils and bind to the local filaments, which then slide into each other. In this way, the muscle fibers of the stylohyoid muscle shorten and pull the hyoid bone backwards and upwards, for example when swallowing. In addition to the suprahyoid muscles, the infrahyoid muscles (lower hyoid muscles) also participate in this process.

Diseases

As the facial nerve joins the musculus stylohyoid to the nervous system, damage to the facial nerve can also affect the stylohyoid muscle. Dysphoric disorders summarizes medicine as dysphagia.

One of the possible causes is Alzheimer's disease, which is characterized by progressive damage to the brain, resulting in functional limitations or deficits in the affected areas. Also the Parkinson's disease, which is based on the Nervschwund in the Substantia nigra, or a stroke, the hereditary disease Huntington's chorea or other neurological diseases come as a cause for dysphagia in question. Injuries to the tongue as well as fractures of the midface or the hyoid bone may damage both the muscles and the innervating nerve fibers.

Malformations and neoplasms in the head, diseases of the esophagus and infectious diseases can also contribute to dysphagia, which is reflected in dysfunction of the musculus stylohyoid and other muscles involved. Psychologically induced dysphagia occurs, for example, in the context of phagophobia, which is a disease-worthy strong fear of suffocation or ingestion and colloquially known as choking anxiety.

In the environment of the musculus stylohyoideus also the Eagle syndrome manifests itself. Watt Weems Eagle was the first to describe the condition; it does not directly affect the musculus stylohyoid, but stylohyoid ligament. In Eagle syndrome, calcium salts are incorporated into the ligament and cause ossification. The syndrome may also be due to the stylus being too long. In both cases, dysphagia such as pain in the throat and difficulty in swallowing are typical when turning the head.

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