The cricoarytaenoideus posterior muscle represents an internal laryngeal muscle. Its function is to widen the glottis, which allows breath to pass through the larynx. Therefore, bilateral paralysis of the cricoarytaenoideus posterior muscle (postictal paralysis) leads to shortness of breath – unilateral paralysis often manifests as hoarseness.
What is the posterior cricoarytaenoid muscle?
The cricoarytaenoideus posterior muscle is a muscle of the larynx. Physicians also call it the posticus; its counterpart is the anticus. This corresponds to the chin-tongue muscle (Musculus genioglossus), which is part of the external tongue musculature. The names “posticus” and “anticus” are predominantly used in connection with pathological conditions. The cricoarytaenoideus posterior muscle is the only one capable of dilating the glottis. Since no other muscle can replace it, it occupies a critical position in voice production and respiration. The laryngeal muscles can be divided into an external and an internal group. The external laryngeal muscles are represented by the cricothyroid muscle. The cricoarytaenoideus posterior muscle, along with seven other muscles, belongs to the inner group. The other internal laryngeal muscles are:
- Musculus cricoarytaenoideus lateralis.
- Musculus arytaenoideus transversus
- Musculus arytaenoideus obliquus
- Musculus aryepiglotticus
- Musculus thyreoarytaenoideus
- Musculus thyreoepiglotticus
- Musculus vocalis
To protect the larynx, the epiglottis closes the throat structure during swallowing. This process also preserves the cricoarytaenoideus posterior muscle from contact with fluid and food.
Anatomy and structure
The cricoarytaenoideus posterior muscle originates at the cricoid cartilage (cartilago cricoidea) of the larynx. This cartilage has the shape of a ring, the actual ring being the arch (arcus) of the cartilage. The plate (lamina) of the cartilago cricoidea points posteriorly. The origin of the posterior cricoarytaenoideus muscle is at this cartilaginous plate. From there, the internal laryngeal muscle extends to the stellate cartilage (cartilago arytaenoidea), where it attaches to the processus muscularis. The stellate cartilage is another part of the larynx. Anatomists also refer to this cartilage as the pouring can cartilage or ary cartilage. In addition to the muscular process, the cartilage also has another process, known as the vocal process, which serves as the attachment for the vocal cord. Not only does the cricoarytaenoideus posterior muscle attach to the processus muscularis, but also the cricoarytaenoideus lateralis muscle. The articulatio cricoarytaenoidea and the ligamentum cricoarytaenoideum form a joint between the positional cartilage and the cricoid cartilage in the larynx.
Function and Tasks
The function of the posterior cricoarytaenoideus muscle is to dilate the glottis. None of the other muscles are able to do this, although some other laryngeal muscles influence the tension of the vocal cords. For example, the vocalis muscle (Musculus vocalis) is responsible for the inherent tension of the vocal cords. Because of its unique feature, the cricoarytaenoideus posterior muscle is particularly important. The inferior laryngeal nerve, which is the last branch of the recurrent laryngeal nerve, is responsible for controlling the posterior cricoarytaenoid muscle. Through other branches, the inferior laryngeal nerve also supplies the other internal laryngeal muscles. In contrast, the external laryngeal muscles in the form of the cricothyroid muscle depend on innervation by the superior laryngeal nerve. The inferior laryngeal nerve 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 excite the muscle fibers of the posterior cricoarytaenoid muscle. Within the muscle, protein structures then push into each other, shortening the length of the fibers: The muscle contracts. As the cricoarytaenoideus posterior muscle tenses, it pulls on the muscular process to which it is attached. This part of the stellate cartilage thus moves backward and widens the glottis, also known as the 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 pass between them. On the other hand, when the glottis widens, air passes through the throat and can cause the vocal folds or vocal cords to vibrate and produce sound in this way.
Diseases
Failure of the posterior cricoarytaenoid muscle is referred to in medicine as posticular palsy. In the case of bilateral paralysis, the glottis is closed and blocks the airway. As a result, dyspnea and respiratory sounds may occur. The latter manifest as stridor, which results from the altered airflow. In addition, bilateral paralysis may be accompanied by hoarseness. As part of treatment, a tracheotomy is often necessary to allow the affected person to breathe. In some cases, the paralysis is permanent. Unilateral paralysis of the posterior cricoarytaenoid muscle is also possible. Symptomatically, hoarseness is the main symptom. Treatment options include electrical stimulation, surgical correction, and conservative voice therapy. However, which options are considered depends on the individual case. A possible reason for the muscle paralysis is a failure of the recurrent laryngeal nerve. Doctors then speak of recurrent nerve palsy. The nerve itself may be damaged, but a failure of the entire vagus nerve can also be considered as a cause. Since the tenth cranial nerve performs numerous functions and runs through the head, neck, chest and abdomen, vagus paralysis is accompanied by other symptoms. In the case of bilateral vagus palsy, circulatory problems are possible in addition to breathing and swallowing difficulties. Paralysis of the tenth cranial nerve may be due to injury, inflammation, or tumor, for example.
