Layers, Cavities, and Regions

LAYERS OF THE VOCAL FOLDS

As seen in the images above, the vocal folds are composed of five layers, the epithelial layer, superficial lamina propria (SLP), intermediate lamina propria (ILP), deep lamina propria (DLP), and the thyroarytenoid muscle.

These five layers are further divided into three: the cover (epithelial layer and superficial lamina propria); transition (intermediate lamina propria and deep lamina propria); and the body (thyroarytenoid muscle).

The epithelial layer is made of squamous epithelium and is considered the most superficial layer. It is approximately 0.1 mm thick. It assists in fluid retention. According to Prades et al. (2010), among the three lamina propria, the epithelial layer is the least viscous one. Thus, it is the layer that is most easy to set into motion or vibration.

The Reinke's space or the superficial lamina propria (SLP) is a jelly-like substance close to the surface and immediately below the basement membrane. It is elastic in nature and it allows stretching because it is made up of elastic fibers. These fibers cross-layer with the intermediate lamina propria which then provides strength and elasticity to the vocal folds. Moreover, during adduction, the superficial lamina propria cushion the vocal folds. According to Prades et al. (2010), the SLP makes up around 13% of the thickness of the lamina propria and it contains strong birefringent fibers.

The intermediate lamina propria resembles the material of a rubber band since it is an elastic fibrous substance. It adds mechanical integrity to the vocal folds. According to Prades et al. (2010), the deep lamina propria makes up approximately 51% of the thickness of the lamina propria. They also characterized the DLP as a less densely organized layer between the deep and superficial layers.

The deep lamina propria (DLP) is considered as a thread-like collagenous fibrous layer. Unlike the previous types of lamia propria, the DLP is more rigid and less flexible. According to Prades et al. (2010), the DLP has the most densely organized band of collagen fibers and makes up approximately 36% of the thickness of the lamina propria.

The thyroarytenoid muscle, also known as the vocalis muscle, is the main body of the vocal folds. This is also the deepest layer of the vocal folds and is very stiff in nature.

3D Anatomy Tutorial on the Mucosa of the larynx and vocal folds

Vocal Cord Vibration Video by Minoru Hirano, MD

REGIONS OF THE LARYNX

The larynx can be divided into three regions: the supraglottis, glottis, and subglottis.

The supraglottis comprises the upper part of the larynx. It is composed of anything superior to the glottis. It is the area where one can find the ventricle/ false vocal folds. It contains the laryngeal surface of the epiglottis.

The glottis is inferior to the supraglottis and is the narrowest portion of the larynx. This is the level where one can find the tru vocal folds.

The subglottis is the area where pressure builds up. It is located inferior to the glottis. This area begins approximately 5 millimeters below the vocal folds' free margins.

Regions of the Larynx

Source:

https://www.lecturio.com/concepts/larynx/

CAVITIES OF THE LARYNX

The larynx has several cavities or spaces in between its structures. The main cavities of the larynx are as follows:

Aditus laryngis - According to Fahmy (2016), this is also known as the laryngeal inlet. This serves as the aperture between the pharynx and larynx. This is bounded by the aryepiglottic folds laterally and the epiglottis anteriorly.

Vestibule - This is considered as the cavity or space between the aditus laryngis and the false vocal folds.

Laryngeal Ventricle - This is located between the ventricular folds' margins and the true vocal folds. This is also the middle space of the larynx.

Saccule - This is a pouch-like structure that is responsible for mucus secretion and pharyngeal cavity lubrication. It is important to note that the mucus aids in foreign body elimination through trapping them.

Glottis - This is the cavity that is most important for speech production because this is the space between the vocal folds. The size of the glottis dictates the voicing, thus, it is especially significant in the production of voiced consonants and vowels. In adults, the regular size of the glottis is 20 millimeters in length from the anterior to the posterior commissure. Moreover, the glottis is relatively larger during forced breathing as it may reach around 15 mm in length in males and 12 mm in length in females. This is significantly longer than the length at rest, which is 8 mm. The reason behind this change in length during the movement of vocal folds (there is a difference in length during breathing and at rest) is because the glottal area is dependent on the movement and configuration of the vocal folds.

The Laryngeal Cavities

Source:

https://pt.slideshare.net/DrSherifFahmy/the-larynx-anatomy-of-the-neck

REFERENCES

Fahmy, S. (2016, August 20). The Larynx (Anatomy of the Neck). Slideshare. https://pt.slideshare.net/DrSherifFahmy/the-larynx-anatomy-of-the-neck

Fuller, D. R., Pimentel, J. T., & Peregoy, B. M. (2012). Applied anatomy & physiology for speech-language pathology & audiology. Wolters Kluwer/Lippincott Williams & Wilkins Health.

Prades, J.-M., Dumollard, J. M., Duband, S., Timoshenko, A., Richard, C., Dubois, M. D., Martin, C., & Peoc’h, M. (2010). Lamina propria of the human vocal fold: histomorphometric study of collagen fibers. Surgical and Radiologic Anatomy: SRA, 32(4), 377–382. https://doi.org/10.1007/s00276-009-0577-9

Seikel, J. A., Drumright, D. G., & Seikel, P. (2013). Essentials of anatomy & physiology for communication disorders. Delmar Cengage Learning.

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