The cricothyroid muscle is a laryngeal muscle that originates from the cricoid cartilage and attaches to the thyroid cartilage (cartilago thyroidea). Its function is to tension the vocal cord (ligamentum vocale). Damage to the muscle can accordingly result in speech problems.
What is the cricothyroid muscle?
In the human throat, above the thyroid gland, lies the larynx, which consists of three floors. The uppermost part is the supraglottis (vestibule laryngis), the middle one is the glottis (cavitas laryngis intermedia), and the lowest floor corresponds to the subglottis (cavitas infraglottica). In and around the larynx are numerous muscles and cartilages, some of which participate in swallowing and coughing, but also in 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 externus or anticus muscle, or merely the anticus or. This designation is common, especially in clinical usage. The cricothyroid muscle alone represents the external laryngeal musculature. The internal laryngeal musculature, on the other hand, consists of eight different muscles.
Anatomy and structure
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 grouped together in bundles – surrounded by a layer of connective tissue. The cricothyroid muscle is composed of three different parts, which anatomists refer to as the pars horizontalis (“horizontal part”), pars obliqua (“oblique part”) and pars recta (“straight part”). The three parts differ in terms of their origin at the cricoid cartilage arch, but they attach together to the inferior portion of the thyroid cartilage (cartilago thyroidea). The thyroid cartilage has the shape of a signet or ornamental ring and consists of a cartilage plate and an arch (arcus). The first recent publications recognize the pars horizontalis as an independent part. Its tissue structure distinguishes the pars horizontalis from the other components of skeletal muscle. The pars obliqua originates from the posterior region of the cricoid cartilage arch. In contrast, the origin of the pars recta is anterior to the cartilage. From there, the pars recta pulls steeply toward the thyroid cartilage plate.
Function and 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: a right and a left. By pulling on the ligament, the external laryngeal muscle is able to change the pitch of the voice. When the vocal cords are strongly stretched, the sound is higher – on the other hand, if the cricothyroid muscle exerts only a slight pull on the vocal cords, a deeper sound is heard. This change is the result of the airflow that passes through the glottis and causes the air to vibrate. The ear perceives these vibrations as sounds. To stretch the vocal cord, the cricothyroid muscle pulls the cricoid cartilage backward and upward. The pull is the result of the shortening (contraction) of the muscle fibers. The muscle receives the signal to contract via the superior laryngeal nerve. The nerve branches off from the vagus nerve (cranial nerve X). A nerve signal commanding the muscle to contract passes into the external branch or ramus externus in the superior laryngeal nerve. Its nerve fibers eventually terminate at the muscle fibers of the cricothyroid muscle in a motor end plate, determining its activity. The control of the muscle is automated in adults. The internal laryngeal muscles also participate in the tension of the vocal cord: For example, contraction of the vocalis muscle results in inherent tension of the vocal ligament.
Diseases
The cricothyroid muscle contributes to the tension of the vocal cords, thereby affecting the human voice. Damage to the muscle can therefore lead to speech disorders. Because the cricothyroid muscle is located at the larynx, isolated external injuries are rare. More often, it sustains damage as part of treatments to the thyroid gland. The thyroid gland (thyroid glandula) is located in the neck slightly 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 partially affect the metabolism of the entire organism. In addition to numerous other causes, tumors can also be considered for complaints in the area of the thyroid gland. Doctors often remove such an ulcer surgically. Both during this procedure and during any subsequent radiation therapy, the cricothyroid muscle may be damaged. However, the external laryngeal muscle may also be the target of planned changes. Transsexual women who were male at birth and identify as female sometimes suffer from the fact that their voice sounds too deep and thus masculine. Hormone therapy also affects the voice through administration of female sex hormones, but it cannot fundamentally change the anatomical structure of the larynx and its muscles. If the person decides to undergo gender reassignment, surgical adjustment of the vocal apparatus is also an option in some cases. However, because any surgery carries risks, many doctors recommend speech-only therapy first. Since the cricothyroid muscle tenses the vocal cords by contraction and in this way raises the voice, it plays an important role in this context.
