Larynx
Larynx
Also known as: voice box, Adam's apple
The cartilaginous valve and voice box between the laryngopharynx and trachea (C3–C6) that protects the lower airway, generates voice and allows effort closure of the thorax.
Overview
The larynx is a framework of nine cartilages — three unpaired (thyroid, cricoid, epiglottis) and three paired (arytenoid, corniculate, cuneiform) — joined by membranes, ligaments and synovial joints and moved by intrinsic and extrinsic muscles. Key membranes: the thyrohyoid membrane (pierced by the internal laryngeal nerve and superior laryngeal artery), the quadrangular membrane (lower free edge = vestibular ligament) and the conus elasticus (cricovocal membrane, upper free edge = vocal ligament; its thick anterior part is the median cricothyroid ligament, the site of emergency cricothyroidotomy).
The laryngeal cavity is divided by two pairs of mucosal folds into the vestibule (inlet to vestibular folds), the ventricle (recess between vestibular and vocal folds, extending up as the saccule) and the infraglottic cavity (vocal folds to the lower border of the cricoid). The glottis — vocal folds plus the opening between them (rima glottidis) — is the narrowest part of the adult airway.
The larynx is first and foremost a sphincter: it closes at three levels during swallowing (aryepiglottic folds, vestibular folds, vocal folds) and is elevated beneath the tongue base while the epiglottis tilts over the inlet. Closure of the glottis against expiratory effort (Valsalva) fixes the thorax for lifting, coughing, defecation and childbirth. Phonation is a secondary function.
- Location
Anterior neck, opposite C3–C6 in adults (higher, C1–C4, in infants), below the hyoid and above the trachea; anterior to the laryngopharynx.
Parts & subdivisions
- Largest cartilage; laryngeal prominence.
- Only complete cartilaginous ring; C6.
- Elastic cartilage flap over the laryngeal inlet.
- Pyramidal cartilages that pivot on the cricoid to move the vocal folds.
- Corniculate and cuneiform cartilagesSmall elastic nodules in the aryepiglottic folds that stiffen the margin of the laryngeal inlet.
- False vocal cords.
- True vocal cords; the glottis.
- Move the cartilages to open, close, tense and relax the vocal folds.
Anatomy
- Innervation
Vagus (CN X). Superior laryngeal nerve → internal branch (sensory to mucosa above the vocal folds) and external branch (motor to cricothyroid). Recurrent laryngeal nerve → motor to all other intrinsic muscles and sensory below the vocal folds. The right RLN loops under the right subclavian artery, the left under the arch of the aorta beside the ligamentum arteriosum; both ascend in the tracheo-oesophageal groove close to the inferior thyroid artery.
- Arterial supply
Superior laryngeal artery (from the superior thyroid artery, external carotid) with the internal laryngeal nerve; inferior laryngeal artery (from the inferior thyroid artery, thyrocervical trunk) with the recurrent laryngeal nerve.
- Venous drainage
Superior laryngeal vein → superior thyroid vein → internal jugular vein; inferior laryngeal vein → inferior thyroid vein → left brachiocephalic vein.
- Lymphatic drainage
Supraglottis (rich network) → upper deep cervical nodes; subglottis → prelaryngeal, pretracheal and paratracheal nodes → lower deep cervical nodes. The vocal folds themselves have very sparse lymphatics, so glottic cancer spreads late.
- Relations
Anteriorly: infrahyoid (strap) muscles and skin; laterally: lobes of the thyroid gland and the carotid sheaths; posteriorly: laryngopharynx; superiorly: hyoid bone and tongue base; inferiorly: trachea (thyroid isthmus over tracheal rings 2–4).
- Histology
Vestibule and subglottis: ciliated pseudostratified columnar epithelium with seromucous glands. Vocal folds and the upper epiglottis: non-keratinised stratified squamous epithelium. Thyroid, cricoid and most of the arytenoids: hyaline cartilage (may ossify with age); epiglottis, corniculate, cuneiform and apices/vocal processes of the arytenoids: elastic cartilage.
- Development
Epithelium from foregut endoderm (laryngotracheal groove); cartilages and muscles from the 4th and 6th pharyngeal arches — hence their supply by the superior (4th) and recurrent (6th) laryngeal branches of the vagus. The laryngeal lumen is temporarily occluded and recanalises by week 10; failure causes laryngeal webs or atresia.
Function
- Protects the lower airway during swallowing (sphincteric closure, cough reflex).
- Phonation: produces voice by vibration of the vocal folds.
- Regulates airflow resistance (glottis widens in inspiration, narrows in expiration).
- Effort closure: fixes the thorax for straining (Valsalva), lifting and coughing.
Clinical significance
Recurrent laryngeal nerve palsy
Injury in thyroid/parathyroid surgery, by apical or hilar lung cancer, aortic arch aneurysm or mediastinal nodes (left more often — longer course) leaves the fold in a paramedian position: unilateral palsy → hoarse, breathy voice and weak cough; bilateral palsy → both folds near the midline with stridor and airway obstruction that may need tracheostomy.
Cricothyroidotomy
In a "can't intubate, can't oxygenate" emergency the airway is accessed through the median cricothyroid ligament, palpable as a soft depression between the thyroid and cricoid cartilages; it lies below the vocal folds and is relatively avascular.
Croup and laryngeal cancer
Croup (laryngotracheobronchitis, usually parainfluenza virus) causes subglottic oedema in children: barking cough, inspiratory stridor, "steeple sign" on AP radiograph. Laryngeal squamous cell carcinoma (smoking, alcohol) presents early with hoarseness when glottic.
Mnemonics
Cartilages
Unpaired: "The Cat Eats" (Thyroid, Cricoid, Epiglottis). Paired: "All Cute Cats" (Arytenoid, Corniculate, Cuneiform).
Compiled from standard anatomy and physiology references — see the Respiratory System sources. For education only; not medical advice.