The glottis (Rima glottidis) is the variable space between the vocal folds (vocal cords) that allows phonation (voice production). The ancient Greek word glottis means in German mouthpiece of a tube. A glottis is composed of the pars intermembranacea and the pars intercartilaginea. The pars intermembranacea is the section between the vocal cords. This makes up approximately 60 percent of the length of a glottis. During voiced speech, the pars intermembranacea is open, but during unvoiced whispering it is closed. The pars intercartilaginea is located between the two processus vocales of the stellate cartilages. This area is closed during phonation and open during whispering. In this way, the contraction of the cricoarytaenoideus lateralis muscle forms the so-called whisper triangle.
What is the glottis?
The width and length of the glottis are thus the decisive parameters for voice formation, speech sounds, and phonation types. They are influenced by the respective position of the positional cartilages. These can be brought together or apart. The width of the glottis changes accordingly from a narrow gap to a wide triangle. In addition, the articular cartilages perform various rotational movements that also regulate the width of the glottis and the degree of tension of the vocal folds. The widening and narrowing of the glottis repeat cyclically. When the airflow increases, the vocal folds finally open gradually to let it pass. When the air pressure drops again, the vocal folds regain their original shape and also resume their previous position. This vibration of the vocal folds is called the Bernoulli effect. The law, developed in the 18th century by Daniel Bernoulli and others, states that the faster the air flows, the lower the pressure.
Anatomy and structure
The vocal folds and glottis are important components of the larynx. It lies on the outside of the throat and forms the transition to the trachea. In addition to voice formation, the larynx ensures that food does not enter the trachea. The voice is formed when the glottis causes exhaled air to vibrate. The frequency of the air vibrations determines the pitch of the voice. When an opera singer sings an extremely high note, for example, the vocal folds open and close up to 1000 times per second. The voice gets its volume with the help of resonance chambers in the lungs and sinuses. The so-called chest voice (chest resonance) arises in this context when the lungs predominantly provide the resonance space. In this case, the voice is comparatively carried and dark. The head voice, on the other hand, owes its bright and higher tone predominantly to the resonance in the paranasal sinuses.
Function and tasks
The mutual positioning of the two vocal folds in relation to each other is made possible by the connection of their posterior ends with the stellate cartilages. Above the vocal folds lie the so-called pouch folds. Under irregular conditions, the pocket folds are involved in voice formation, which is why they are also called “false vocal cords.” In such a case, the voice sounds brittle and artificially compressed (“pocket fold voice”). The voice may be interrupted by a brief closure of the glottis. This results in a typical cracking sound. Something similar happens due to a spontaneous closure of the larynx. Malformations of the glottis and vocal cords can be examined relatively easily with a laryngoscope (laryngeal mirror). A stroboscope, which emits flashes of light, can visualize the oscillatory behavior of the vocal folds. Finally, a laryngograph is a very good way to record the vibrations of the vocal cords.
Diseases
A common disease of the voice-forming apparatus is paralysis of the vocal folds. In many cases, it occurs on one side, but if it occurs on both sides, it can lead to serious obstructions to breathing. The vocal cords can no longer move apart to the required extent. A considerable disturbance of the airflow is the result. Under certain circumstances, this dangerous occurrence can only be remedied surgically. The cause of vocal cord paralysis is often damage to the recurrent nerve (inferior laryngeal nerve). It may be preceded, for example, by a thyroid operation in the course of which this nerve was injured or even cut.Lung cancer or other malignant tumors in the neck and chest area also threaten to severely affect this nerve. In addition, the paralysis may have inflammatory causes. Bilateral paralysis of the vocal folds leads to shortness of breath even at rest. The voice is often only slightly altered, sounding somewhat weak and brittle. When breathing in, however, a rasping, wheezing sound can be heard. However, any small disorder in the airway immediately and very significantly increases the respiratory distress. In contrast, a unilateral vocal fold paralysis usually manifests itself only in slight hoarseness, which, however, also leads to breathing problems during greater physical exertion. Targeted vocal cord training can be relatively effective in improving the condition of unilateral paralysis. In mild cases, unilateral vocal fold paralysis also disappears on its own. If surgery is necessary to cure bilateral vocal cord paralysis, one of the two vocal folds is pulled outward in a common procedure (laterofixation). This allows the necessary distance between the two vocal cords to be restored. Removing one of the two vocal cords also achieves the goal. This procedure must always be performed under general anesthesia. By means of modern devices, this operation can also be performed from the inside through the mouth, but this only marginally reduces the risk of complications.
