Vocal folds

Plicae vocales

Also known as: vocal cords, true vocal cords, glottis, rima glottidis

Paired mucosal folds stretched from the thyroid angle to the arytenoid vocal processes, containing the vocal ligament and vocalis muscle, that vibrate to produce voice and close to protect the airway.

Overview

Length≈17–25 mm (men), ≈12–17 mm (women)

Fundamental frequency≈100–120 Hz (men), ≈200–220 Hz (women)

Each vocal fold consists of the vocal ligament (thickened upper edge of the conus elasticus), the vocalis (medial part of thyroarytenoid) and a covering mucosa. The mucosa has a layered structure: non-keratinised stratified squamous epithelium; the gelatinous superficial lamina propria (Reinke's space) that ripples in the "mucosal wave"; and the intermediate and deep layers forming the vocal ligament. The folds appear pearly white because they lack submucosal vessels and glands. The gap between them, the rima glottidis, has an anterior intermembranous part (≈3/5) and a posterior intercartilaginous part (≈2/5); folds plus rima form the glottis.

Phonation (myoelastic–aerodynamic theory): the folds are adducted, subglottic pressure builds and blows them apart, then elastic recoil and the Bernoulli effect draw them together again, producing rapid cycles of vibration. Pitch rises with tension and length (cricothyroid) and falls with mass; loudness depends on subglottic pressure. Typical fundamental frequency is ≈100–120 Hz in men and ≈200–220 Hz in women. Quiet breathing keeps the rima moderately open; forced inspiration abducts it widely.

Location

Within the larynx at the level of the middle of the thyroid cartilage, below the vestibular folds and laryngeal ventricle.

Parts & subdivisions

Vocal ligament

Elastic ligament from the thyroid angle to the vocal process; upper free margin of the conus elasticus.

Vocalis muscle

Medial fibres of thyroarytenoid; fine-tunes tension along the fold.

Reinke's space

Superficial lamina propria; essential for vibration.

Rima glottidis

Variable aperture between the folds; narrowest part of the adult larynx.

Anatomy

Innervation

Motor via the recurrent laryngeal nerve (all intrinsic muscles except cricothyroid, which is supplied by the external laryngeal nerve). Sensory: mucosa above the folds — internal laryngeal nerve; at and below — recurrent laryngeal nerve.

Lymphatic drainage

Almost no lymphatics in the free margin, so early glottic carcinoma rarely metastasises.

Histology

Non-keratinised stratified squamous epithelium over a three-layered lamina propria; no submucosal glands in the free edge.

Clinical significance

Vocal fold nodules and polyps

"Singer's nodules" are bilateral, symmetrical swellings at the junction of the anterior third and posterior two-thirds — the point of maximal vibratory impact — from voice overuse. Reinke's oedema is diffuse swelling of Reinke's space in smokers, producing a low, husky voice.

Glottic carcinoma

Squamous cell carcinoma of the vocal folds causes hoarseness early and spreads to lymph nodes late, so it has a good prognosis; any hoarseness persisting > 3 weeks in a smoker warrants laryngoscopy.

Vocal fold paralysis

Recurrent laryngeal nerve palsy leaves the fold paramedian: unilateral → breathy voice and aspiration risk; bilateral → stridor and airway obstruction.

Test yourself

Which intrinsic laryngeal muscle is the only abductor of the vocal folds?

Lateral cricoarytenoid
Cricothyroid
Transverse arytenoid
Posterior cricoarytenoid

Answer: Posterior cricoarytenoid

The posterior cricoarytenoid rotates the arytenoid cartilages laterally, abducting the vocal processes and opening the rima glottidis. Bilateral paralysis (e.g. bilateral recurrent laryngeal nerve injury) leaves the folds near the midline and can cause life-threatening stridor.