Histology of the vocal cords

Age-related changes in the macula flava influence the fibrous components of the vocal folds and are partially responsible for the differences in the acoustics of the adult and aged voice.

The histological structure of the vocal fold can be separated into 5[2] or 6[3] tissues, depending on the source, which can then be grouped into three sections as the cover, the transition, and the body.

[5] The next three layers comprise lamina of lipopolysaccharides (LPs), which are stratified by their histological composition of elastin and collagen fibers, with fibroblast, myofibroblast and macrophages interspersed sparsely.

In normal vocal folds, the jelly-like "Reinke's space" is very loose and abundant with interstitial proteins such as hyaluronic acid, fibronectin, proteoglycan like fibromodulin, decorin and versican.

All these extracellular matrix components together regulate the water content of vocal fold and render the viscous shear property for it.

[8][9] The squamous epithelium and superficial lamina propria form the vocal mucosa which serves as vibratory component in phonation.

[7] Elastin fibers impart the flexibility and elasticity of the vocal folds and, collagen is responsible for the resistance and resiliece to tensile strength.

[11] The normal strain level of vocal ligament ranges from 0–15% during phonation[7] These fibrous proteins exhibit distribution variations spatially and temporally due to fibroblast turnover during tissue maturation and aging.

Lubrication of the vocal folds through adequate hydration is essential for normal phonation to avoid excessive abrasion, and the microridges and microvilli help to spread and retain a mucous coat on the epithelium.

[13] The superficial layer of the lamina propria is a structure that vibrates a great deal during phonation, and the viscoelasticity needed to support this vibratory function depends mostly on extracellular matrices.

The primary extracellular matrices of the vocal fold cover are reticular, collagenous and elastic fibers, as well as glycoprotein and glycosaminoglycan.

These fibers serve as scaffolds for structural maintenance, providing tensile strength and resilience so that the vocal folds may vibrate freely but still retain their shape.

The transition layer is primarily structural, giving the vocal fold support as well as providing adhesion between the mucosa, or cover, and the body, the thyroarytenoid muscle.