The cricothyroid muscle is a laryngeal muscle originating from the cricoid cartilage and attached to the thyroid cartilage (Cartilago thyroidea). Its task is to stretch the vocal cord (ligamentum vocale). Damage to the muscle can result in language problems.

What is the cricothyroid muscle?

In the neck of the human above the thyroid gland lies the larynx, which consists of three floors. The uppermost part is the supraglottis (vestibulum laryngis), the middle one is the glottis (Cavitas laryngis intermedia) and the bottom floor is the subglottis (Cavitas infraglottica).

In the larynx and around it are numerous muscles and cartilage, which participate partly in the swallowing and coughing, but also in the speech. The cricothyroid muscle is one of these muscles: its tension is transmitted to the tension of the vocal cord. In medicine, the cricothyroid muscle is also known as the external or anticus muscle or merely the anticus or respectively. This term is common in clinical usage. The cricothyroid muscle alone represents the external laryngeal musculature. The internal laryngeal muscles, however, consists of eight different muscles.

Anatomy & Construction

As a striated skeletal muscle, the cricothyroid muscle forms part of the musculoskeletal system of the human body. It consists of muscle fibers that are bundled together - surrounded by a layer of connective tissue.

The cricothyroid muscle is composed of three distinct parts, which designate the anatomy as pars horizontalis, pars obliqua (oblique part) and pars recta (straight part). The three parts differ in their origin from the circular cartilaginous arch, but together they attach to the lower part of the thyroid cartilage (Cartilago thyroidea). The thyroid cartilage has the shape of a seal or jewelery ring and consists of a cartilaginous plate and an arc (Arcus).

First recent publications recognize the Pars horizontalis as an independent part. Their tissue structure separates the pars horizontalis from the other components of the skeletal muscle. The pars obliqua arises from the posterior part of the circular cartilaginous arch. In contrast, the origin of the pars recta lies at the front of the cartilage. The pars recta pulls from there steeply to the thyroid cartilage.

Function & Tasks

In the larynx, the cricothyroid muscle contributes to the formation of sounds. Its function is to stretch the vocal cord (ligamentum vocale), of which each person has a total of two: one right and one left. By pulling on the ligament, the outer laryngeal muscle is able to change the pitch of the voice. When the vocal cords are strongly strained, the tone sounds higher - on the other hand, the cricothyroid muscle exerts only a slight pull on the vocal cords, a deeper sound sounds. This change is the result of the breeze that penetrates the glottis and sets the air in vibration. These vibrations perceive the ear as sounds.

To tighten the vocal cord, the cricothyroid muscle pulls the cricoid cartilage back and forth. The pull is the result of shortening (contraction) of the muscle fibers. The signal to contract receives the muscle over the upper laryngeal nerve (superior laryngeal nerve). The nerve branches off from the vagus nerve (cranial nerve X). A nervous signal, which gives the muscle the command to contraction, passes into the external branch or external ramus in the superior laryngeal nerve.

Its nerve fibers finally end at the muscle fibers of the cricothyroid muscle in a motor end plate and thus determine its activity. The control of the muscle is automated in adults. The inner laryngeal muscles also have an effect on the tension of the vocal cords. For example, a contraction of the vocalis muscle leads to the residual tension of the ligamentum vocale.

Diseases

The cricothyroid muscle contributes to the tension of the vocal cords and thereby influences the human voice. Damage to the muscle can therefore lead to speech problems. Because the cricothyroid muscle is located on the larynx, isolated external injuries are rare.

More often, he takes damage as part of thyroid treatments. The thyroid (Glandula thyroidea) is located in the neck a little lower than the larynx, where it produces the hormones L-triiodothyronine (T3) and L-thyroxine (T4). Various diseases can disrupt the functioning of the thyroid gland. Due to the endocrine tasks of the glandula tyhroidea, such diseases partly affect the metabolism of the entire organism. Among many other causes tumors are also considered for complaints in the area of ​​the thyroid gland. Doctors often remove such an ulcer surgically. The cricothyroid muscle can be damaged both in this case and in subsequent radiotherapy.

However, the external laryngeal muscle may also be the target of planned changes. Transsexual women who were male at birth and identify as female partly suffer from the fact that their voice sounds too deep and therefore masculine. Hormone therapy also affects the voice through the use of female sex hormones, but it can not fundamentally alter the anatomical structure of the larynx and its muscles.

If the person chooses to be sexually assimilated, in some cases an operative adaptation of the vocal tract can be considered. However, as every operation involves risks, many physicians initially recommend pure speech therapy. Since the cricothyroid muscle contractes the vocal cords by contracting it and thus raises the voice, it plays an important role in this context.

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