Musculus Constrictor Pharyngis Medius: Structure, Function & Diseases

The constrictor pharyngis medius muscle is a pharyngeal muscle and consists of two parts. It is responsible for constricting the pharynx of the mouth, thereby pushing food or fluid toward the esophagus (food pipe). Functional limitations of the constrictor pharyngis medius muscle are often manifested in swallowing and speech disorders.

What is the constrictor pharyngis medius muscle?

The constrictor pharyngis medius muscle belongs to the pharyngeal musculature and, within this group, is one of the pharyngeal lacing muscles. The superior pharyngeal constrictor (Musculus constrictor pharyngis superior) and the inferior pharyngeal constrictor (Musculus constrictor pharyngis inferior) immediately adjoin the Musculus constrictor pharyngis medius on both sides, but represent anatomic units that are distinct from it. The three muscles develop from different gill arches in the embryonic stage, with the Musculus constrictor pharyngis medius arising from the fourth gill arch. This also contains the anlagen for the inner and outer laryngeal muscles (laryngeal muscles), for muscles of the esophagus, and for various vessels, nerves, and cartilages. The other two pharyngeal constrictors develop from the third and sixth gill arches. The constrictor pharyngis medius muscle belongs to the skeletal musculature and can be influenced voluntarily. It also has a striated structure with a pattern formed by alternating filaments within the muscle fibers.

Anatomy and structure

Anatomically, the middle pharyngeal constrictor can be divided into two sections: the pars ceratopharyngea and the pars chondropharyngea. Both parts of the musculus constrictor pharyngis medius originate from the hyoid bone (Os hyoideum), but have their origin there in different places: The pars ceratopharyngea begins at the small horn (cornu majus), whereas the pars chondropharyngea originates at the large horn (cornu minus). The hyoid bone (corpus ossis hyoidei) extends between the two horns. The hyoid bone does not have its own connection to other bones, but is attached to the suprahyoid and infrahyoid muscles, as well as some pharyngeal and lingual muscles. At the pharyngeal suture (raphe pharyngis) is the insertion of the musculus constrictor pharyngis medius. The upper and lower pharyngeal lacing muscles also attach there. Overall, the constrictor pharyngis medius muscle has the shape of a fan or funnel. Nerve fibers connect the muscle to the pharyngeal plexus, which consists of branches of the ninth cranial nerve (glossopharyngeal nerve) and portions of the tenth cranial nerve (vagus nerve).

Function and tasks

The constrictor pharyngis medius muscle participates in the swallowing process and participates in the formation of certain sounds, which include posterior low vowels and pharyngeal sounds. The swallowing act can be divided into a preparatory phase, which includes, for example, chewing, and three transport phases. During the oral transport phase, mainly the tongue muscles are active and push the food or liquid from the front of the mouth into the pharynx. This is followed by the pharyngeal transport phase, which is crucial for the constrictor pharyngis medius muscle. First, the tensor veli palatini muscle and the levator veli palatini muscle tighten the soft palate. The superior constrictor pharyngis muscle creates a bulge in the nasopharynx (epipharynx) by contraction, also known as Passavant’s annular bulge. This, together with the soft palate, closes the entrance to the nose. The digastric muscle, mylohyoid muscle and stylohyoid muscle pull or lift the os hyoideum upward together with the infrahyoid and suprahyoid muscles. At the same time, the thyrohyoid muscle also ensures that the larynx is lifted so that the epiglottis can close it. At the same time, the upper esophageal sphincter dilates the esophagus. The annular sphincter is located in the upper esophageal jugular (constrictio pharyngooesophagealis) and forms the esophageal orifice. When all airways are closed, the constrictor pharyngis medius muscle contracts, pushing food or fluid further back in the throat. The constrictor pharyngis inferior muscle assists it in this process. In the subsequent esophageal transport phase, the muscles of the esophagus finally take over the further transport into the stomach. The entire process is highly automated and controlled by the swallowing center of the brain.

Diseases

Damage to the constrictor pharyngis medius muscle rarely occurs in isolation, but often affects the other pharyngeal muscles as well as other structures. Loss of function of the muscle is often neuronal. Swallowing disorders, also known as dysphagias, can affect all phases and aspects of the swallowing act: from closure of the nose and larynx to lifting of the hyoid bone as well as pushing food forward. Sensitivity and salivation may also be affected. Numerous possibilities can be considered as the cause of dysphagia. In addition to direct injury (such as from an accident), nerve damage is the most common cause. Radiation therapy for treatment of breast carcinoma may inadvertently damage the pharyngeal plexus, which also controls the constrictor pharyngis medius muscle. The vagus nerve and glossopharyngeal nerve, along with the accessorius nerve, pass through the zygomatic vein (jugular foramen), through which blood vessels also pass. Tumors, hemorrhages, swellings, injuries and other damage at this site therefore frequently affect all three nerves and accordingly trigger very complex clinical pictures. Neuromuscular and neurodegenerative diseases can also affect the fibers controlling the constrictor pharyngis medius muscle. So can brain injuries and circulatory disorders such as strokes and congenital neuroanatomical abnormalities. Because the constrictor pharyngis medius muscle is not only involved in the swallowing process but also contributes to the formation of certain sounds, motor speech disorders are also possible. Under certain circumstances, affected persons can improve their speech ability again through logopedic training. However, success depends on the individual case at hand.