The cricothyroid muscle is the sole intrinsic laryngeal muscle innervated by the external branch of the superior laryngeal nerve (eSLN) rather than the recurrent laryngeal nerve. It has two portions: the pars recta (anterior, nearly vertical) and the pars obliqua (posterior, oblique toward the inferior cornu). Together they tilt the cricothyroid joint to increase vocal fold tension for pitch raising, particularly in the upper pitch register.
| Origin | Anterolateral surface of the cricoid cartilage (lateral arch) |
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| Insertion | Pars recta: anterior inferior margin of the thyroid cartilage lamina; Pars obliqua: inferior horn of the thyroid cartilage |
| Nerve Supply | External branch of the superior laryngeal nerve (from CN X) — the only intrinsic laryngeal muscle NOT supplied by the recurrent laryngeal nerve |
| Blood Supply | Superior laryngeal artery; cricothyroid branch |
| Actions | Tilts the thyroid cartilage anteriorly and inferiorly relative to the cricoid (or equivalently tilts the cricoid posteriorly), increasing the distance between the thyroid cartilage angle and the arytenoids, thereby lengthening and tensioning the vocal folds to raise pitch; the primary tensor of the vocal folds for high-pitched phonation |
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The external branch of the superior laryngeal nerve runs along the inferior pharyngeal constrictor to reach the cricothyroid — this nerve is at risk during thyroidectomy as it may descend with the superior thyroid artery before reaching the cricothyroid muscle. Injury to the eSLN produces subtle voice changes (loss of high-pitched phonation, reduced vocal range) that are particularly disabling for singers and professional voice users but may be missed on routine post-thyroidectomy voice assessment. Cernea classification of eSLN position relative to the superior thyroid vessels guides surgical protection.
The external branch of the superior laryngeal nerve descending with the superior thyroid artery (Cernea type 2b) is ligated with the vessel during high ligation of the superior thyroid pole, denervating the cricothyroid and producing loss of high-pitched phonation and reduced vocal range particularly devastating for singers; identification of the nerve before superior pole ligation prevents this complication.
