Larynx anatomy
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Larynx Anatomy
Overview
The larynx is a hollow musculoligamentous structure with a cartilaginous framework that caps the lower respiratory tract. It lies in front of the C3-C6 vertebrae (slightly higher in women), extending from the laryngeal inlet down to the inferior border of the cricoid cartilage. It serves two primary functions:
- Valve/sphincter to protect the lower airway during swallowing
- Sound production (phonation)
Motor and sensory innervation is via the vagus nerve [CN X].
(Gray's Anatomy for Students)
Divisions of the Larynx
The larynx is divided into three compartments by the false and true folds:
| Region | Boundaries |
|---|---|
| Supraglottis | Epiglottis + aryepiglottic folds down to the apex of the laryngeal ventricle |
| Glottis | From apex of ventricle, includes the true vocal folds, anterior and posterior commissures |
| Subglottis | From ~1 cm below the free edge of vocal folds to the inferior border of the cricoid |
Note: "Vocal cord" is anatomically inaccurate - "vocal fold" is preferred, as these structures vibrate in a multiplanar (not simply cord-like) fashion. (Scott-Brown's Otorhinolaryngology)
Laryngeal Cartilages
The framework includes 3 unpaired and 3 paired cartilages:
Unpaired Cartilages
1. Cricoid Cartilage
- Most inferior laryngeal cartilage; the only one that completely encircles the airway
- Shaped like a signet ring: broad posterior lamina + narrow anterior arch
- Posterior lamina has two oval depressions (for posterior cricoarytenoid muscles) separated by a vertical ridge (for esophageal attachment)
- Has articular facets for arytenoid cartilages (superolateral lamina) and inferior thyroid horns (lateral lamina)
2. Thyroid Cartilage (largest)
- Formed by right and left laminae that fuse anteriorly as the laryngeal prominence (Adam's apple)
- Thyroid angle: ~90° in men, ~120° in women - this is why the prominence is more visible in men
- Each lamina has superior and inferior horns (cornua):
- Superior horn connects via the lateral thyrohyoid ligament to the greater horn of hyoid
- Inferior horn articulates with the cricoid at the cricothyroid joint (synovial)
- Oblique line on the lateral surface: attachment for sternothyroid, thyrohyoid, and inferior constrictor muscles
3. Epiglottis
- Leaf-shaped; attached by its stem via the thyroepiglottic ligament to the posterior thyroid angle, midway between laryngeal prominence and inferior thyroid notch
- Projects posterosuperiorly; upper margin lies behind the pharyngeal tongue
- Also attached to hyoid by hyoepiglottic ligament - the space between these two ligaments is the pre-epiglottic space
- Its posterior surface has an epiglottic tubercle and numerous mucosal pits for mucous glands
- The mucous membrane reflects onto the tongue as the glossoepiglottic fold (midline) and lateral glossoepiglottic folds, forming the valleculae
Paired Cartilages
4. Arytenoid cartilages - pyramid-shaped, sit on the sloping shoulders of the cricoid lamina; have a vocal process (attachment of vocal ligament) and a muscular process (attachment of most intrinsic muscles)
5. Corniculate cartilages - small, at the apex of arytenoids; form the posterior limit of the aryepiglottic folds
6. Cuneiform cartilages - within the aryepiglottic folds, providing support
Membranes and Ligaments
Extrinsic
- Thyrohyoid membrane: fibroelastic sheet from upper thyroid cartilage to hyoid bone; reinforced centrally as median thyrohyoid ligament and posteriorly as lateral thyrohyoid ligaments (which often contain a sesamoid nodule, the cartilago triticea). Pierced by the internal branch of the superior laryngeal nerve and superior laryngeal vessels
- Cricotracheal ligament: joins inferior cricoid border to first tracheal ring
Intrinsic (Fibroelastic Membrane)
Divided by the laryngeal ventricle into upper and lower parts:
| Part | Name | Free Margin |
|---|---|---|
| Upper | Quadrangular membrane | Lower free margin = vestibular ligament (under false vocal cord) |
| Lower | Conus elasticus (cricothyroid ligament) | Upper free margin = vocal ligament (under true vocal cord) |
- The median cricothyroid ligament is the thickened anterior midline portion of the conus elasticus - the site used for emergency cricothyrotomy
- The laryngeal ventricle (sinus) is the lateral recess between the vestibular and vocal folds
Joints
| Joint | Type | Movement |
|---|---|---|
| Cricothyroid | Synovial | Thyroid tilts forward/downward on cricoid → lengthens and tenses vocal folds |
| Cricoarytenoid | Synovial | Arytenoids rock and rotate → abducts/adducts vocal folds |
Intrinsic Muscles
All intrinsic muscles are innervated by the recurrent laryngeal nerve (RLN) - except the cricothyroid, which is innervated by the external branch of the superior laryngeal nerve (SLN).
| Muscle | Action | Nerve |
|---|---|---|
| Posterior cricoarytenoid (PCA) | Abducts vocal folds (opens rima glottidis) - the ONLY abductor | RLN |
| Lateral cricoarytenoid (LCA) | Adducts vocal folds | RLN |
| Transverse arytenoid | Adducts arytenoids (closes posterior glottis); only unpaired muscle | RLN |
| Oblique arytenoid | Sphincter of laryngeal inlet | RLN |
| Thyroarytenoid | Shortens/relaxes vocal folds; sphincter of vestibule | RLN |
| Vocalis (medial part of thyroarytenoid) | Fine tension adjustment of vocal folds | RLN |
| Cricothyroid | Tilts thyroid forward, elongating and tensing vocal folds (raises pitch) | External SLN |
The cricothyroid is the only intrinsic muscle that lies outside the cartilaginous framework of the larynx. (Scott-Brown's)
Neurovascular Supply
Innervation (both from CN X - Vagus)
- Superior laryngeal nerve (SLN):
- Internal branch: sensory to larynx above the vocal folds; pierces thyrohyoid membrane
- External branch: motor to cricothyroid muscle
- Recurrent laryngeal nerve (RLN): motor to all other intrinsic muscles; sensory below vocal folds. On the right, loops around the subclavian artery; on the left, loops around the aortic arch
Blood Supply
- Superior laryngeal artery (from superior thyroid artery, branch of external carotid) - accompanies the internal branch of the SLN through the thyrohyoid membrane
- Inferior laryngeal artery (from inferior thyroid artery, branch of thyrocervical trunk)
Lymphatic Drainage
- Supraglottis: rich lymphatic drainage to upper and middle deep cervical nodes - this is why supraglottic tumors spread early
- Glottis: virtually no lymphatics - explains why glottic cancers metastasize late
- Subglottis: drains to paratracheal and lower deep cervical nodes
Clinical Notes
- Infant larynx: funnel-shaped with the narrowest point at the subglottic-tracheal junction (not the glottis as in adults); positioned higher in the neck; softer cartilages prone to collapse
- After puberty, the AP diameter of the male larynx nearly doubles (~36 mm men vs ~26 mm women)
- The pre-epiglottic space and the paraglottic spaces are filled with loose connective tissue - important routes for tumor spread
- RLN injury (e.g., from thyroid surgery, mediastinal tumors) causes ipsilateral vocal fold paralysis; bilateral injury causes respiratory distress
Sources: Scott-Brown's Otorhinolaryngology Head & Neck Surgery; Gray's Anatomy for Students (Gray's Anatomy for Students, p. 1192-1201)
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