The omohyoideus muscle is one of the sublingual muscles. It also represents an auxiliary respiratory muscle and is involved in chewing.
What is the omohyoid muscle?
The lower hyoid muscles are also known as the infrahyoid muscles and include not only the omohyoideus muscle, but also the levator glandulae thyroideae muscle, the sternohyoideus muscle, the sternothyroideus muscle, and the thyrohyoideus muscle. These five muscles participate in swallowing and belong to the striated skeletal musculature. The striated pattern is due to the structure of the tissue: within a muscle there are numerous muscle fibers (muscle cells), each consisting of several myofibrils. These can be divided into transverse segments, which anatomists refer to as sarcomeres. A sarcomere is bounded by the Z-disks and has two types of filaments. These are strands of myosin on the one hand and a complex of tropomyosin and actin on the other. These two protein structures are arranged alternately and can push into each other, causing the muscle to shorten and thus contract.
Anatomy and structure
The omohyoid muscle has an intermediate tendon that connects the two bellies of the muscle. It originates from the scapula (shoulder blade) and attaches to the inferior hyoid body (os hyoideum). Anatomy also refers to the upper part of the omohyoid muscle as the superior venter (“upper belly”). This muscle belly is located near the sternohyoideus muscle, which, like the omohyoideus muscle, belongs to the infrahyoid musculature. The inferior venter (“upper belly”) of the omohyoideus muscle extends upward in the neck. In its fine structure, the omohyoideus muscle consists of muscle fibers that correspond to muscle cells and contain many nuclei. Surrounding the muscle fiber is a membrane that demarcates it from adjacent tissue. Small tubes, the T-tubules, pass through the membrane and are located at the level of the Z-disks of the sarcomeres. Within the membrane are several myofibrils, which are filamentous strands. In the interstices, analogous to the endoplasmic reticulum in other cell types, lies the sarcoplasmic reticulum. Mitochondria are responsible for cellular respiration and play a central role in energy metabolism, which is why they are also known as the “powerhouses of cells.”
Function and tasks
The ansa cervicalis profunda connects the omohyoid muscle to the nervous system and controls its activity. The ansa cervicalis profunda is the deep part of the cervical nerve loop, which also innervates the other muscles of the infrahyoid musculature. The signals of the nerve loop originate from the cervical plexus. The ansa cervicalis profunda runs transverse to the internal jugular vein. Oxygen-depleted blood flows through this vein from the head back toward the lungs. The omohyoideus muscle is responsible for keeping the internal jugular vein open by tightening the middle cervical fascia (lamina praetrachealis). The omohyoideus muscle can also pull the hyoid bone downward posteriorly by contracting. This movement is particularly relevant during swallowing. Several muscles work together in this process: In addition to the infrahyoid muscles, the floor of the mouth muscles (suprahyoid muscles) and the muscles of the palate are also active during swallowing. Subsequently, the tunica muscularis of the esophagus (food pipe) assists in transporting food or fluid into the stomach. The swallowing center in the medulla oblongata coordinates the swallowing process and triggers the swallowing reflex. Via the ninth and tenth cranial nerves (glossopharyngeal and vagus nerves), the swallowing center receives sensitive information and uses various neural pathways to trigger the motor response in the corresponding muscles. Neural structures involved include the ninth to twelfth cranial nerves, the fifth cranial nerve, and the cervical plexus, which also controls the omohyoid muscle. Furthermore, the omohyoideus muscle participates in certain head movements. When a person moves his head forward, the infrahyoid muscles (including the omohyoideus muscle) provide a countermovement of the hyoid bone downward backward. In its function as an auxiliary respiratory muscle, the omohyoideus muscle also assists breathing to a lesser degree.
Diseases
One of the roles of the omohyoid muscle is to keep the internal jugular vein open. Medical professionals use this vein in part to place a central venous catheter (CVC). To do this, they insert a thin tube into the vein and push it inside the blood vessel to the front of the right atrium. A central venous catheter is used in various situations. For example, doctors can use it to determine the central venous pressure, which is an indicator of the preload of the heart and plays an important role in the context of various cardiological diseases. In addition, a CVC allows the administration of various substances close to the heart, including electrolytes and drugs. For the central venous catheter, not only the internal jugular vein is considered, but also the subclavian vein. Beyond these two preferred CVC variants, access can also be gained into the anonyma vein or the basilica vein, and less frequently via other veins. Damage and functional limitations of the omohyoid muscle may contribute to dysphagia. Neurologic disorders, such as those associated with stroke or neurodegenerative disease, may damage the nerve fibers responsible for supplying the omohyoid muscle and the rest of the infrahyoid musculature. In addition, injuries, tumors, and other lesions in the medulla oblongata may affect the swallowing center and interfere with the coordinated swallowing process. The swallowing reflex may also be affected.
