Pharynx
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Direct answer
Twelve to fourteen centimetres of muscular tube, the pharynx runs from the base of the skull to the lower border of the cricoid cartilage at C6, behind the nasal, oral and laryngeal cavities. Three overlapping constrictors — superior, middle and inferior — form its wall, and the gaps between them transmit the structures that must enter: the auditory tube and levator veli palatini above the superior constrictor, the stylopharyngeus with the glossopharyngeal nerve between superior and middle, and the internal laryngeal nerve with the superior laryngeal artery between middle and inferior. Its motor supply is the pharyngeal plexus of the vagus, and the dehiscence between the two parts of the inferior constrictor is the seat of the pharyngeal pouch.
What you must remember
- Nasopharynx behind the nasal cavity extends to the soft palate; its lateral wall bears the tubal elevation (torus tubarius) with the auditory tube opening, and the recess behind it (fossa of Rosenmuller) is the classical origin of nasopharyngeal carcinoma.
- Oropharynx extends from the soft palate to the tip of the epiglottis; laryngopharynx continues to C6, flanked by the piriform fossae, where fish bones lodge.
- The pharyngeal wall from within outwards: mucosa, submucosa (pharyngobasilar fascia), muscular coat of constrictors, and buccopharyngeal fascia.
- Killian's dehiscence lies between the thyropharyngeal and cricopharyngeal parts of the inferior constrictor — the weakest point, where a pharyngeal pouch (Zenker's diverticulum) protrudes.
- Motor: pharyngeal plexus (cranial accessory fibres in the vagus) to all muscles except stylopharyngeus (glossopharyngeal) and the tensor veli palatini (mandibular nerve).
- Sensory: glossopharyngeal from the nasopharynx and oropharynx, vagus (internal laryngeal) from the laryngopharynx, with the maxillary nerve's pharyngeal branch to the nasopharynx roof.
- The piriform fossae are innervated by the internal laryngeal nerve, so foreign bodies there cause referred ear pain and cough.
Working through two problems written on the constrictor gaps
Take first the elderly man with slowly progressive dysphagia, gurgling on swallowing, halitosis and recurrent aspiration, in whom a barium swallow shows a outpouching above the cricopharyngeus. The anatomy writes the diagnosis: the propulsive thyropharyngeus above and the sphincteric cricopharyngeus below meet at Killian's dehiscence, a triangle of relative weakness; when the sphincter fails to relax in sequence, pressure drives the mucosa out through the dehiscence, usually to the left. The pouch fills with food, compresses the oesophagus and spills into the larynx on reclining. Treatment per current practice is endoscopic stapled diverticulotomy dividing the common wall and the cricopharyngeus, or open diverticulectomy in larger pouches — either way, the operation is on the dehiscence's lower bar, the muscle that failed to relax.
Take second the neurological bed. A stroke patient coughs on swallowing and has a nasal voice. The paretic pharyngeal muscles and the failure of the soft palate to elevate reflect the pharyngeal plexus's vagal supply, while the intact gag reflex's efferent side tests the same plexus; the afferent is glossopharyngeal, so the gag reflex is the cranial nerve IX–X pair's bedside test. Nasopharyngeal carcinoma arising in the fossa of Rosenmuller explains the triad Indian postgraduate exams repeat: conductive deafness from tubal blockage, cranial nerve palsies from skull base extension, and neck nodes — with the internal carotid and the lateral pharyngeal wall being the radiation planner's landmarks.
Where students slip
The gaps between the constrictors and their contents are the perennial slip. The pair stylopharyngeus plus glossopharyngeal nerve between superior and middle constrictors is the one most often exchanged for the internal laryngeal nerve, which belongs lower — between middle and inferior constrictors with the superior laryngeal artery. Second, the tensor veli palatini's nerve is given as "the pharyngeal plexus"; it is the mandibular nerve via the nerve to medial pterygoid, first-arch muscle in a tenth-nerve neighbourhood — the exception examiners ask precisely because it is unique. Third, students describe the inferior constrictor as one muscle; its two parts, thyropharyngeal and cricopharyngeal, with different fibre direction and function, are the whole basis of the pouch, and an answer that omits the two parts has not answered the question.
Frequently asked questions
What passes between the superior and middle constrictors?
The stylopharyngeus muscle and the glossopharyngeal nerve.
What is Killian's dehiscence?
The potential gap between the thyropharyngeal and cricopharyngeal parts of the inferior constrictor, the site of origin of a pharyngeal pouch.
Which nerve supplies all pharyngeal muscles except two?
The pharyngeal plexus, carrying cranial accessory fibres in the vagus — except the stylopharyngeus (glossopharyngeal) and tensor veli palatini (mandibular nerve).
Why does nasopharyngeal carcinoma cause deafness?
The tumour arises near the fossa of Rosenmuller and blocks the auditory tube's pharyngeal opening, producing conductive hearing loss with middle-ear effusion.
At what vertebral level does the pharynx end?
At the lower border of the cricoid cartilage, the C6 level, where it becomes the oesophagus.