Learning objective
By the end of this lesson, learners should be able to differentiate between extrinsic and intrinsic laryngeal muscles, describe their attachments and actions, and understand their innervation and functional roles in phonation and airway movement.
Overview of the larynx and its muscles
The larynx (voice box) is located in the anterior neck and forms part of the respiratory tract. It performs several important functions, including phonation, the cough reflex, and protection of the lower respiratory tract.
The muscles of the larynx are divided into two functional groups:
- Extrinsic muscles: Move the larynx as a whole, elevating or depressing it during swallowing.
- Intrinsic muscles: Act on the individual components of the larynx, controlling the rima glottidis, and adjusting the length and tension of the vocal folds for phonation.
In this lesson, we examine the anatomy, attachments, actions, and innervation of both groups of laryngeal muscles.
Extrinsic muscles
Extrinsic muscles move the larynx superiorly or inferiorly and are composed of:
- Suprahyoid muscles
- Infrahyoid muscles
- Stylopharyngeus (a pharyngeal muscle)
These muscles attach to the hyoid bone, which is bound to the larynx by strong ligaments, allowing coordinated movement of the entire larynx.
Functional rule:
- Suprahyoid muscles and stylopharyngeus → elevate the larynx
- Infrahyoid muscles → depress the larynx
Intrinsic muscles
Intrinsic muscles act on individual laryngeal structures and control:
- Shape of the rima glottidis (space between vocal folds and arytenoids)
- Length and tension of the vocal folds
Innervation:
- All intrinsic muscles → inferior laryngeal nerve (terminal branch of the recurrent laryngeal nerve from CN X), except cricothyroid
- Cricothyroid → external branch of the superior laryngeal nerve (from CN X)
Cricothyroid muscle
- Action: Stretches and tenses the vocal ligament; modulates pitch (“singer’s muscle”)
- Attachments: Originates from the anterolateral cricoid cartilage; inserts on the inferior margin and horn of the thyroid cartilage
- Innervation: External branch of the superior laryngeal nerve
Thyroarytenoid muscle
- Action: Relaxes the vocal ligament; allows a softer voice
- Attachments: Originates from the inferoposterior angle of the thyroid cartilage; inserts on the anterolateral arytenoid
- Innervation: Inferior laryngeal nerve
Posterior cricoarytenoid muscle
- Action: Abducts the vocal folds; the only muscle capable of widening the rima glottidis
- Attachments: Posterior surface of the cricoid → muscular process of the arytenoid
- Innervation: Inferior laryngeal nerve
Lateral cricoarytenoid muscle
- Action: Adducts vocal folds; narrows the rima glottidis to modulate voice tone and volume
- Attachments: Arch of the cricoid → muscular process of the arytenoid
- Innervation: Inferior laryngeal nerve
Transverse and oblique arytenoid muscles
- Action: Adduct the arytenoid cartilages; close the posterior rima glottidis; narrow the laryngeal inlet
- Attachments: From one arytenoid cartilage → opposite arytenoid cartilage
- Innervation: Inferior laryngeal nerve
