The cricoarytaenoideus posterior muscle represents an internal laryngeal muscle. Its function is to dilate the glottis, allowing the air to pass through the larynx. Bilateral paralysis of the cricoarytaenoideus posterior muscle (postikus paralysis) therefore causes respiratory distress - unilateral paralysis often manifests as hoarseness.

What is the cricoarytaenoideus posterior muscle?

The musculus cricoarytaenoideus posterior is a muscle of the larynx. Doctors also call him Postikus; its counterpart is the Antikus. This corresponds to the chin-tongue muscle (genioglossus muscle), which belongs to the outer tongue muscles.

The names "postikus" and "anticus" are mostly used in connection with pathological conditions. The cricoarytaenoideus posterior is the only one able to enlarge the glottis. Since no other muscle can replace it, it occupies a critical position in voice formation and breathing.

The laryngeal muscles can be divided into an outer and an inner group. The outer laryngeal musculature represents the cricothyroid muscle. The cricoarytaenoideus posterior muscle belongs to the inner group with seven other muscles. The other internal laryngeal muscles are:

  • Cricoarytaenoideus lateralis muscle
  • Musculus arytaenoideus transversus
  • Musculus arytaenoideus obliquus
  • Aryepiglotticus muscle
  • Thyreoarytaenoideus muscle
  • Thyreoepiglotticus
  • Musculus vocalis

To protect the larynx, the epiglottis closes the neck structure during swallowing. This process also preserves the posterior cricoarytaenoideus muscle from contact with fluid and food.

Anatomy & Construction

The cricoarytaenoideus posterior muscle originates from the cricoid cartilage (Cartilago cricoidea). This cartilage has the shape of a ring, with the actual ring representing the arc of the cartilage.

The plate (lamina) of the Cartilago cricoidea points to the rear. The origin of the cricoarytaenoideus posterior muscle is located on this cartilaginous plate. From there, the inner laryngeal muscle extends to the cartilage (Cartilago arytaenoidea), where it attaches to the processus muscularis.

The arytenoid cartilage is another part of the larynx. The anatomy refers to this cartilage as a watering can or arytenoid cartilage. In addition to the muscular process, the arytenoid cartilage also has another process known as the processus vocalis, which serves as an attachment to the vocal cord. At the processus muscularis not only the musculus cricoarytaenoideus posterior, but also the musculus cricoarytaenoideus lateralis begins. The articulatio cricoarytaenoidea and the cricoarytaenoid ligament form a joint in the larynx between the arytenoid cartilage and the cricoid cartilage.

Function & Tasks

The cricoarytaenoideus posterior has the task of dilating the glottis. None of the other muscles are capable of doing so, although some other laryngeal muscles affect the tension of the vocal cords. The voice muscle (Musculus vocalis), for example, is responsible for the residual stress of the vocal cords. Because of its unique selling point, the cricoarytaenoideus posterior muscle is particularly important.

For the control of the cricoarytaenoideus posterior muscle, the inferior laryngeal nerve is responsible, which represents the last branch of the recurrent laryngeal nerve (recurrent laryngeal nerve). The lower laryngeal nerve (inferior laryngeal nerve) also supplies the other internal laryngeal muscles via other branches. In contrast, the external laryngeal musculature in the form of the cricothyroid muscle relies on innervation by the superior laryngeal nerve (superior laryngeal nerve). Nervus laryngeus inferior and superior laryngeal nerve each form a branch of the vagus nerve (cranial nerve X).

When action potentials reach the end of the motor nerve fibers, they irritate the muscle fibers of the cricoarytaenoideus posterior muscle. As a result, protein structures interlock within the muscle, thereby shortening the length of the fibers: the muscle contracts. As the cricoarytaenoideus posterior muscle tightens, it pulls on the muscular processus to which it is attached. This part of the arytenoid cartilage moves backwards and widens the glottis, also known as Rima glottidis.

When the glottis is closed, the two vocal folds (plicae vocales) meet in the middle of the larynx, so that no air can flow between them. On the other hand, when the glottis widens, the air passes through the throat, causing the vocal folds or vocal cords to vibrate, producing sounds in the process.

Diseases

The failure of the musculus cricoarytaenoideus posterior is what medicine calls postoperative paralysis. In case of bilateral paralysis, the glottis is closed and blocks the respiratory tract. As a result, respiratory distress and secondary breathing may occur.

The latter manifest as stridor, which is created by the changed air flow. In addition, bilateral palsy may be associated with hoarseness. As part of the treatment, a tracheotomy is often necessary to allow the person concerned to breathe. In some cases, the paralysis is permanent.

Unilateral paralysis of the posterior cricoarytaenoideus muscle is also possible. Hoarseness is most symptomatic. Treatment options include electrical stimulation, surgical corrections, and conservative vocal therapy. However, which options are possible depends on the individual case.

The reason for the muscle paralysis is a failure of the Nervus laryngeus recurrens in question. Doctors then speak of recurrent paralysis. In this case, the nerve itself may be damaged, but the cause is also a failure of the entire vagus nerve into consideration. As the tenth cranial nerve carries out numerous functions and moves through the head, neck, chest and abdomen, vagus paralysis is accompanied by further symptoms. In a bilateral vagal nerve palsy in addition to respiratory and swallowing disorders and circulatory disorders are possible. Paralysis of the tenth cranial nerve may be due, for example, to injury, inflammation or a tumor.

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