Corpus: Vestibular fold

The plica vestibularis is a paired fold of tissue in the region of the larynx, which is raised by the vestibular ligament and borders the vestibular rima.

The two vestibular plicae lie directly above the vocal folds (plicae vocales). They can be mistaken for the latter during laryngoscopy and are therefore also referred to as "false" vocal folds. The vestibular plicae separate the laryngeal vestibule (supraglottis) from the laryngeal ventricle below it.

There are numerous tubuloalveolar, seromucous glands in the vestibular plicae. The plicae may also contain isolated tracts of striated muscle, which are then addressed as the ventricularis muscle. This muscle is more pronounced in animals.

Due to the downwardly directed inner curvature, the pocket folds offer a regulating resistance to the outflowing air. Consequently, they are an exhalation or pressure relief valve. However, they do not have any significant muscle structures. Their constriction is based on the activity of the surrounding muscles (palatal, pharyngeal and laryngeal muscles) and the expiratory respiratory muscles. This is a complex, reflex-mediated movement programme.

The vocal folds (inhalation or negative pressure valves) and the vestibular plicae form two opposing valves (laryngeal double valve function).

The vestibular plicae are involved in the laryngeal fold-closure mechanism during swallowing. Together with the closure of the epiglottis and vocal folds, their constriction serves to protect the lower airways from aspiration.

The laryngeal closing mechanism also serves to regulate the pressure conditions in the thorax and abdomen. It is important for various physiological processes:

• In the event of aspiration - with simultaneous activity of the expiratory muscles - the build-up of intrathoracic pressure is ensured. This enables coughing or clearing the throat.
• The closure leads to an increase in intra-abdominal pressure when the abdominal press is applied, e.g. during defecation or childbirth.
• When force is applied away from the body (e.g. punching or kicking), the closure of the pocket folds and simultaneous activation of the expiratory respiratory muscles leads to stabilisation of the trunk.

A further function of the pocket folds is to moisturise and clean the (gland-free) vocal folds with their glandular secretions by means of a kind of stroking movement.

As an exhalation valve, the vestibular plicae also regulate the speed of the outflowing air. In this way, they prevent the air from escaping too quickly and contribute to adequate gas exchange in the lungs.

In contrast to the vocal folds, the vestibular plicae are generally not involved in phonation.

Excessive activation of the exhalation muscles results in the pocket folds coming closer together. This can lead to vocal fatigue and dysphonia.

If the final or vibrational quality of the vocal folds is disturbed, the overpressure system is involuntarily activated and favoured over phonation. The reason for this is that, from an evolutionary biology perspective, protective functions (e.g. protection against aspiration) take precedence over phonation, which is evolutionarily younger and not vital.

Under certain conditions, a so-called pocket fold voice also occurs. This causes the vestibular plicae to vibrate and thus contribute to phonation. The pocket fold voice can be used as a symptom of an illness, as a substitute voice in the case of vocal fold paralysis or voluntarily as a way of singing.

• Pressman, Sphincters of the Larynx, A.M.A. Archives of otolaryngology, 1954
• Negus, The Mechanism of The Larynx, Laryngoscope, 1957
• Rohmert, Grundzüge des funktionalen Stimmtrainings, Zeitschrift für Arbeitswissenschaft, 1987
• Reiß, Facharztwissen HNO-Heilkunde, Springer Medizin Verlag, 2009
• Kruse, Functional Laryngology, 1st edition, Urban & Fischer Verlag, 2012
• Rabine, Keys to voice, 1st edition, Peter Ewers publishing house, 2019