Pharynx and larynx

Pharynx

• Constrictors (superior, middle, inferior), palatopharyngeus and salpingopharyngeus: vagus through the pharyngeal plexus. Stylopharyngeus: IX, its only muscle.
• Sensory: nasopharynx V2; oropharynx IX (gag reflex afferent; efferent X); laryngopharynx X. The pharyngeal plexus (IX sensory, X motor) supplies the oro- and nasopharynx.
• Killian's dehiscence: weak area between the thyropharyngeus and cricopharyngeus parts of the inferior constrictor. A pharyngeal pouch (Zenker) herniates here: elderly patient, dysphagia, regurgitation of undigested food, halitosis, gurgling neck swelling.
• Cricopharyngeus is the upper oesophageal sphincter at C6.

Tonsil and peritonsillar abscess

• Main artery: tonsillar branch of the facial artery; post-tonsillectomy venous bleeding from the paratonsillar (external palatine) vein; glossopharyngeal nerve in the bed (referred ear pain, the nerve most at risk).
• Lymph to the jugulodigastric node.
• Quinsy: pus outside the tonsil capsule pushes the uvula to the opposite side; trismus from spasm of the adjacent medial pterygoid. (Tetanus trismus is masseter spasm.)
• Recurrent streptococcal pharyngitis risks rheumatic fever and post-streptococcal glomerulonephritis.

Pharyngeal arches

• The oropharyngeal (buccopharyngeal) membrane and the cloacal membrane are the two sites where ectoderm and endoderm touch with no mesoderm between; the former ruptures to open the mouth.

Larynx: framework and levels

• Thyroid cartilage (C4–C5), cricoid (complete ring, C6), epiglottis, paired arytenoids, corniculates, cuneiforms.
• Cricothyroid membrane: emergency airway between thyroid and cricoid.
• Thyroid isthmus over tracheal rings 2–4. A thyroidea ima artery (from the brachiocephalic trunk or arch, about 10%) may cross the trachea below the isthmus. Tracheostomy bleeding commonly comes from the inferior thyroid and anterior jugular veins; in children the brachiocephalic vessels rise into the neck and are at risk.
• The rima glottidis is the narrowest part of the adult airway; the cricoid ring in young children.

Vocal fold structure

• Layers: stratified squamous epithelium, superficial lamina propria (Reinke's space), vocal ligament (intermediate and deep lamina propria), vocalis muscle.
• Reinke's oedema: smokers; floppy, jelly-like swelling along the whole cord in the superficial lamina propria; deep gruff voice.
• Vocal nodules ("singer's or teacher's nodules"): symmetrical, at the junction of the anterior and middle thirds, the point of maximum vibration.
• Glottic carcinoma: early hoarseness, and the cords have very few lymphatics, so nodal spread is rare and cure rates high. Supraglottic cancer is silent and spreads to nodes early.
• Laryngomalacia: commonest cause of infant stridor; omega-shaped epiglottis, short aryepiglottic folds collapsing on inspiration, worse supine and feeding; usually outgrown.

Intrinsic muscles and nerves

• Superior laryngeal nerve divides into the internal laryngeal (sensory above the cords; pierces the thyrohyoid membrane with the superior laryngeal artery; cough reflex) and the external laryngeal (cricothyroid; runs with the superior thyroid artery to the upper pole).
• Recurrent laryngeal nerve: sensory below the cords, motor to all other intrinsic muscles; left loops under the aortic arch, right under the subclavian; runs in the tracheo-oesophageal groove, close to the inferior thyroid artery, and is most at risk at the ligament of Berry.
• Internal laryngeal block for awake intubation: needle just below the greater horn of the hyoid, through the thyrohyoid membrane.

Nerve injuries and cord positions

• Paralysis of the posterior cricoarytenoid leaves the cord in an adducted position; the cords are abducted only by that muscle.
• A left recurrent laryngeal palsy (sluggish left cord, hoarse voice) may come from thoracic causes: lung cancer, aortic aneurysm, mitral stenosis enlarging the left atrium.

Palate in vagal lesions

• Levator veli palatini (vagus) lifts the soft palate. After a left jugular foramen lesion (IX, X, XI), the left levator is paralysed and the intact right side pulls the uvula to the right, away from the lesion; nasal voice and nasal regurgitation follow.

Swallowing

• Oral phase (voluntary). Pharyngeal phase (reflex, medullary swallowing centre): soft palate closes the nasopharynx, larynx rises under the tongue, epiglottis tilts, cords close, breathing stops briefly, cricopharyngeus relaxes. Oesophageal phase: peristalsis.
• Bulbar palsy: dysphagia and nasal regurgitation. A swallowed coin stimulating the vagus can cause reflex bradycardia.

Remember Posterior cricoarytenoid opens; cricothyroid tightens; everything else closes or relaxes on the recurrent nerve.

Exam trap Upper pole and superior thyroid artery: external laryngeal; lower pole and inferior thyroid artery: recurrent laryngeal.

Exam trap The uvula deviates away from a vagal lesion.

How FCPS asks about this

• Only abductor of the vocal cords: posterior cricoarytenoid (recurrent laryngeal).
• Singer loses high notes after thyroidectomy: external laryngeal nerve, injured at the superior pole.
• Hoarseness after tying the inferior thyroid artery: recurrent laryngeal nerve.
• Trismus in quinsy: medial pterygoid spasm.
• Why early glottic cancer rarely spreads to nodes: vocal folds have very few lymphatics.
• Site of vocal nodules: junction of anterior and middle thirds.
• Derivatives of the third arch: stylopharyngeus, greater horn of hyoid, IX.