Larynx — Anatomy & Nerve Supply

Cartilages

Cartilage	Number	Note
Thyroid	Single	The largest laryngeal cartilage
Cricoid	Single	The only complete ring in the airway — signet-ring shaped, which is what makes cricoid pressure work
Epiglottis	Single	Leaf-shaped, elastic cartilage
Arytenoid	Paired	Sits on the cricoid; the vocal ligaments attach here
Corniculate	Paired	On the apex of the arytenoids
Cuneiform	Paired	In the aryepiglottic folds

Single: thyroid, cricoid, epiglottis. Paired: arytenoid, corniculate, cuneiform.
The thyrohyoid membrane is pierced by the superior laryngeal artery and the internal branch of the superior laryngeal nerve — the landmark for a superior laryngeal nerve block.
The larynx sits at C3–C6 in the adult, higher (C2–C3) in the infant.

Sternohyoid — depresses the larynx.
Thyrohyoid — elevates the larynx. Supplied by C1 fibres travelling with the hypoglossal nerve.
Inferior constrictor — part of the constrictor sequence of the pharynx.

Intrinsic muscle	Action on vocal cords	Paired?	Nerve
Cricothyroid	Tenses and lengthens the cords	Paired	External branch of the superior laryngeal nerve
Posterior cricoarytenoid	ABDUCTS — the only abductor	Paired	Recurrent laryngeal
Lateral cricoarytenoid	ADDUCTS	Paired	Recurrent laryngeal
Aryepiglottic	Closes the laryngeal inlet	Paired	Recurrent laryngeal
Thyroarytenoid	Relaxes / shortens the cords	Paired	Recurrent laryngeal
Transverse arytenoid	Closes the glottis (constrictor)	UNPAIRED — the only one	Recurrent laryngeal

ALL intrinsic muscles are supplied by the recurrent laryngeal nerve EXCEPT the cricothyroid, which is supplied by the external branch of the superior laryngeal nerve.
The posterior cricoarytenoid is the only ABDUCTOR. Mnemonic: "Posterior Cricoarytenoid Opens" — PCO opens the cords. Everything else closes them.
The transverse arytenoid is the only unpaired intrinsic muscle.

Superior laryngeal (internal br.)	Recurrent laryngeal	Glossopharyngeal
Base of the tongue Posterior epiglottis Aryepiglottic folds Arytenoids	Vocal cords Trachea	Posterior ⅓ of tongue Vallecula Anterior epiglottis Pharyngeal walls Tonsils

Superior laryngeal artery — from the superior thyroid artery, a branch of the external carotid. Pierces the thyrohyoid membrane.
Inferior laryngeal artery — from the inferior thyroid artery, a branch of the thyrocervical trunk.
Venous drainage follows the arteries to the internal jugular vein.

Nerve injured	Muscles affected	Clinical result
Unilateral recurrent laryngeal	All intrinsic muscles except cricothyroid, on that side	Hoarseness. Cord lies in a paramedian position; the other cord compensates
Bilateral recurrent laryngeal	All intrinsic except cricothyroid, both sides	Both cords in the midline → stridor and airway obstruction. AN EMERGENCY — may need reintubation or tracheostomy
Superior laryngeal — external branch	Cricothyroid	Weak, monotonous voice — the cord cannot be tensed, so pitch is lost
Superior laryngeal — internal branch	None (purely sensory)	Loss of sensation above the cords → risk of ASPIRATION
Vagus, unilateral	All laryngeal muscles on that side	Hoarseness
Vagus, bilateral	All laryngeal muscles, both sides	Aphonia

The only abductor is the posterior cricoarytenoid, supplied by the RLN. Lose both RLNs and nothing opens the cords.
The cricothyroids remain innervated (external branch of the SLN) and keep tensing the cords, holding them in the midline.
Result: stridor and complete airway obstruction — classically presenting after thyroid surgery.
Contrast with bilateral vagal injury, where the cricothyroids are also denervated: the cords sit in a cadaveric intermediate position, giving aphonia rather than obstruction.