Structure: cartilages and cavity
The larynx is a framework of nine cartilages joined by membranes and moved by small muscles. Three are single and three are paired.
| Cartilage | Key features |
|---|---|
| Thyroid | Two laminae meeting at the laryngeal prominence; superior and inferior horns; hyaline |
| Cricoid | The only complete cartilage ring in the airway, with its broad lamina behind; lower border at C6; hyaline |
| Epiglottis | Leaf-shaped, attached by its stalk to the back of the thyroid cartilage; elastic |
| Arytenoids | Pyramids on the cricoid lamina; vocal process in front, muscular process laterally; mostly hyaline |
| Corniculate and cuneiform | Small nodules in the aryepiglottic folds; elastic |
The hyaline cartilages can calcify with age and show on radiographs; the elastic ones do not. Inside, the cavity has three parts: the vestibule above the vestibular folds, the ventricle (laryngeal sinus) between the vestibular and vocal folds, and the infraglottic cavity below the vocal folds, continuous with the trachea. The gap between the vocal folds is the rima glottidis, the narrowest part of the adult airway.
The laryngeal inlet and folds
The laryngeal inlet is the opening into the larynx, bounded by the upper edge of the epiglottis, the aryepiglottic folds on each side and the mucosa between the arytenoids behind. Each aryepiglottic fold runs from the side of the epiglottis back to the arytenoid, and the cuneiform and corniculate cartilages raise small tubercles in its posterior part.
- Vestibular fold (false cord): the upper, thicker, pink fold covering the vestibular ligament. It has little role in voice but closes to hold the breath.
- Vocal fold (true cord): the lower, sharp, pale fold. It covers the vocal ligament, the thickened upper free edge of the conus elasticus (cricothyroid membrane), with vocalis muscle beneath. Its surface is stratified squamous epithelium.
- Piriform fossa: the recess of the laryngopharynx lateral to each aryepiglottic fold, where swallowed food passes and fish bones lodge.
The tongue in front of the larynx
The dorsum of the tongue is divided by the V-shaped sulcus terminalis into an oral anterior two-thirds and a pharyngeal posterior third. The apex of the V points backwards to the foramen caecum, the site where the thyroid gland began its descent as the thyroglossal duct.
- Vallate papillae: about eight to twelve large, flat-topped papillae in a row just in front of the sulcus terminalis, each sunk in a trench lined with taste buds. They are supplied by the glossopharyngeal nerve despite lying in front of the sulcus.
- Fungiform papillae: red, mushroom-shaped dots scattered among the filiform papillae, most numerous at the tip and sides, carrying taste buds.
- Filiform papillae: the most numerous, giving the dorsum its velvet texture, without taste buds.
Behind the sulcus the surface is nodular with the lingual tonsil. The valleculae lie between the tongue base and the epiglottis, either side of the median glosso-epiglottic fold.
Blood supply and innervation
The larynx is supplied by the superior and inferior laryngeal arteries and innervated entirely by the vagus. The superior laryngeal artery (from the superior thyroid) enters with the internal laryngeal nerve through the thyrohyoid membrane; the inferior laryngeal artery (from the inferior thyroid) accompanies the recurrent laryngeal nerve.
| Nerve | Motor | Sensory |
|---|---|---|
| Internal laryngeal | None | Mucosa above the vocal folds, including the piriform fossa |
| External laryngeal | Cricothyroid | None |
| Recurrent laryngeal | All other intrinsic muscles | Mucosa below the vocal folds |
Posterior crico-arytenoid is the only muscle that abducts the vocal folds. Lateral crico-arytenoid and the transverse and oblique arytenoids adduct them, cricothyroid tenses them, and thyro-arytenoid with vocalis shortens and adjusts them. The tongue's anterior two-thirds has general sensation from the lingual nerve (V3) and taste from the chorda tympani (VII); its posterior third has both from the glossopharyngeal nerve (IX).
Clinical relevance
Laryngeal disease shows as voice change, stridor or aspiration, and most of it traces back to the nerve supply.
- Unilateral recurrent laryngeal palsy: the fold lies near the midline; the voice is hoarse and breathy and the cough weak.
- Bilateral recurrent laryngeal palsy: both folds lie near the midline, so the voice may be fair but the airway is narrow; stridor after thyroidectomy is an emergency.
- External laryngeal injury: loss of pitch range and voice fatigue, often from ligating the superior thyroid pedicle away from the gland.
- Glottic carcinoma: presents early with hoarseness and spreads late because the vocal folds have few lymphatics.
- Foreign body in the piriform fossa: the internal laryngeal nerve lies just under its mucosa and can be injured during removal.
On the specimen
The specimen is viewed from above and behind, as at laryngoscopy, with the tongue in front and the laryngeal inlet behind it.
- Vestibular or vocal fold: the vestibular fold is higher, broader and pinker; the vocal fold is lower, sharper and paler, with the ventricle as a slit between them.
- Arytenoid or epiglottis: the arytenoid bump is at the back end of the aryepiglottic fold; the epiglottis is the leaf at the front of the inlet.
- Laryngopharynx or larynx: anything lateral or posterior to the aryepiglottic folds, including the piriform fossae, is laryngopharynx.
- Vallate or fungiform papillae: vallate papillae are large and form the V row in front of the sulcus terminalis; fungiform papillae are small red dots near the tip.