Codex @codex  0

Entry of material into the airways from the mouth, pharynx or stomach.

The glossopharyngeal nerve is a mixed ninth cranial nerve: it carries pharyngeal and lingual sensation, posterior tongue taste, carotid sensory input, motor fibres to stylopharyngeus, and a secretomotor route to the parotid gland. Its connections explain why its name alone understates its functions.

Rootlets leave the lateral medulla oblongata, behind the olive and above those of the vagus nerve. They cross the posterior cranial fossa and leave through the jugular foramen. Superior and inferior sensory ganglia lie at or near that passage. The cervical trunk descends in relation to the internal carotid artery and internal jugular vein, then turns forwards around stylopharyngeus. It reaches the pharyngeal wall between the superior and middle constrictors and divides towards the posterior tongue, tonsillar region and pharynx. Its topographical association with the vagus does not make the two nerves functionally identical.

The tympanic branch returns through the inferior tympanic canaliculus into the middle ear. Its tympanic plexus supplies the mucosa of the tympanic cavity, auditory tube and related air spaces and communicates with carotid sympathetic fibres. Preganglionic parasympathetic fibres continue through the lesser petrosal nerve to the otic ganglion. Postganglionic fibres then reach the parotid gland with the auriculotemporal nerve, a branch of the mandibular division of the trigeminal nerve. This is a useful example of fibres originating in one cranial outflow and travelling for their last segment with another nerve.^[ref]

The branch to stylopharyngeus is motor; contraction elevates and expands the pharynx during swallowing. Pharyngeal branches contribute to the pharyngeal plexus, together with the vagus nerve and sympathetic connections. The principal motor supply of the pharyngeal constrictors is vagal: membership of a mixed plexus does not justify assigning every fibre or every pharyngeal muscle to the ninth nerve. Tonsillar branches supply the palatine tonsil and neighbouring mucosa. Lingual branches carry ordinary sensation and taste from the posterior third of the tongue, including the vallate papillae even though these lie just anterior to the terminal groove.

The carotid sinus nerve carries information from pressure-sensitive endings in the carotid sinus and from the carotid body's chemical sensors. The first contributes to regulation of blood pressure; the second responds especially to arterial oxygen deficiency, with responses also influenced by carbon dioxide and acidity. These are afferent functions, distinct from the motor and secretory branches.^[ref]

In the modern central account, branchial motor fibres arise from the nucleus ambiguus, parasympathetic fibres from the inferior salivatory nucleus, visceral and taste afferents project towards the solitary nucleus, and relevant general sensory fibres project to the spinal trigeminal system. These nuclear and reflex distinctions refine the gross anatomical description available in 1864. Pharyngeal touch can initiate swallowing and contributes to the afferent limb of the gag reflex, whose principal motor limb is vagal. Ordinary sensation, taste, pharyngeal movement and secretion therefore need separate observations; the absence of one response does not by itself prove loss of every ninth-nerve function.^[ref]

Local treatment is useful when there is an accessible lesion or a defined symptom to relieve; its concentration, delivered quantity and route must be specified separately. Historical indications included chronic pharyngitis with excessive secretion, ulceration, enlarged or unhealthy tonsillar surfaces, and some forms of chronic laryngitis. The intended effects were cleansing, soothing, reducing secretion, or cauterising a circumscribed unhealthy surface. Merely having a sore throat was not sufficient reason for a caustic application.

The accessible pharynx could be treated by a gargle, a wash, a lozenge, or a carefully directed brush or sponge. A gargle does not reliably medicate the larynx: during normal swallowing the entrance is protected, and aspiration is an unwanted event. For laryngeal painting, the period apparatus included a light source, reflector, small warmed laryngeal mirror and a suitably bent brush. Illumination and the mirror image allowed inspection of the lesion and guidance of the instrument, instead of blind probing. A small measured loading reduced uncontrolled flow into the airway. An atomiser instead broke liquid into droplets with a jet of air or steam; the concentration in its reservoir was not the amount retained by the patient. A contemporary review discusses brushes, mirrors, caustic holders and the limitations of spraying caustic solutions.^[ref]

For a numerical period example, the 1865 account of medicated inhalation gives silver nitrate, 3–5 grains, sometimes 10 grains, per Imperial fluid ounce of distilled water. These are historical reservoir concentrations, approximately 0.7–2.3 percent mass per volume, not oral doses and not modern recommendations for inhaling a corrosive. Other concentrations in the same 1865 account, each per fluid ounce of water, are tannic acid, 3–10 grains; alum, 4–15 grains; zinc sulfate, 1/2–5 grains; and opium tincture, 1–10 minims. The first three were intended chiefly as local astringent applications, and the last as a soothing or narcotic application. These are reports of historical practice, including hazardous applications, rather than evidence that atomising these drugs is beneficial or safe today.^[ref]

Direct historical cauterisation used still stronger silver nitrate solutions or the solid salt for selected ulcers and growth bases. A contemporary review records disagreement over aggressive treatment and reports a recommendation of 40 grains per fluid ounce in one of the works reviewed. That disagreement is part of the answer: 40 grains per ounce for local painting must not be confused with a dilute gargle, an inhalation concentration or a swallowed dose. For a less destructive mode of local medication, the period dosage table lists one to four or more tannic acid lozenges, illustrating again the distinction between strength per item and the number administered.^[ref][ref]

Modern uncomplicated acute sore throat usually receives symptom relief, adequate drinking, and selective antibiotic treatment when indicated by the assessed cause and severity. Medicated lozenges can give a small reduction in pain in adults; that modest benefit does not validate the historical corrosive sprays. Persistent hoarseness, a focal ulcer or a suspected growth requires diagnosis rather than repeated empirical painting. Stridor, difficulty managing secretions or respiratory distress raises an airway problem, for which irritating instrumentation can be hazardous. Local treatment of a syphilitic or other specific lesion cannot replace systemic treatment of its cause.^[ref][ref]

The Eustachian tube, or auditory tube, connects the middle ear with the nasopharynx. Its principal functions are ventilation and pressure equalization, clearance of middle-ear secretions, and protection against inappropriate entry of nasopharyngeal material.

Developmentally, its lumen and epithelial lining arise chiefly from the proximal part of the tubotympanic recess, an extension of the first pharyngeal pouch. The expanded distal part contributes to the tympanic cavity. The neighbouring first pharyngeal cleft is associated with the external ear passage and must not be substituted for the pouch as the origin of the auditory tube. Supporting cartilage and connective tissue develop from surrounding mesenchyme. At birth the tube is shorter and more nearly horizontal; craniofacial growth lengthens it and changes its orientation. The developmental account distinguishes formation of the channel from later growth of its surrounding structures.^[ref]

In an adult the auditory tube is roughly 3.5–4 cm long. From its tympanic opening in the anterior wall of the middle ear, it runs forwards, downwards and medially towards its pharyngeal opening in the lateral wall of the nasopharynx, behind the nasal cavity. Its lateral third is bony, lying in the temporal bone; the medial two thirds are chiefly cartilaginous with a membranous part. The narrow junction is the tubal isthmus. The cartilaginous portion is normally collapsed, so an open passage for sound or reflux does not continuously connect pharynx and middle ear.

The bony part is closely related medially to the canal of the internal carotid artery; the canal for the tensor tympani muscle lies above it. The medial cartilaginous part rests towards the skull base. Its pharyngeal end makes the tubal prominence, or torus tubarius, near the soft palate. The tensor veli palatini muscle acts on the cartilaginous and membranous tube and is the main active dilator. The levator veli palatini muscle passes beneath it and participates in the palatal and tubal functional arrangement. Swallowing and yawning intermittently open the tube.^[ref]

Opening permits gas transfer to compensate for a difference between middle-ear and ambient pressure. If the tube remains obstructed, absorption of gas from the cavity can make middle-ear pressure fall; movement of the tympanic membrane and sound transmission then change. Clearance is helped by the mucociliary lining, which carries material towards the nasopharynx. Closure between openings limits reflux and transmission of nasopharyngeal pressure disturbances. A tube that remains persistently open therefore also functions abnormally; more openness is not invariably better.

The physiological point can be demonstrated by observing the tympanic membrane while swallowing during a change of external pressure, or by recording the membrane's mechanical response over a controlled range of ear-canal pressures using tympanometry. These observations examine pressure communication and membrane mobility, not merely whether air can be forcibly driven through a passage. The relatively immature geometry and opening mechanism in young children helps explain their vulnerability to middle-ear fluid retention, but geometry alone is not an exhaustive account of infection risk. The anatomical structures were recognizable in 1866; the modern measurement method should not be mistaken for apparatus supplied by the examination.

A free reed is a thin elastic tongue fixed at one end over a closely fitting opening in a rigid frame. A pressure difference drives an airflow; displacement of the tongue alters the available opening, and the changing aerodynamic force can sustain its vibration against elastic restoring force and damping. Unlike a beating reed, the tongue passes through the opening without regularly striking its rim. The air supply provides the energy; the reed's dimensions and stiffness largely set the pitch, while its enclosure and any attached pipe modify the response and radiated sound waves.

The useful analogy with phonation is an airflow-driven valve coupled to an elastic oscillator. Air from the lungs passes between the vocal folds in the larynx. Their motion periodically modulates the flow, generating a rich sound spectrum; the pharynx, mouth and nasal passages filter it, while the tongue and lips help form speech sounds. The vocal folds are paired living tissues with adjustable tension and geometry, rather than a single metal tongue. Their oscillation should not be explained as a passive string struck repeatedly by air, nor does the free-reed analogy establish every detail of tissue motion. ^[ref]

Changing vocal-fold tension and effective vibrating mass changes the source pitch. Changing the resonating passages changes its spectral envelope and the vowel quality. Those are different controls: a singer can change pitch while retaining a recognisable vowel, or change vowel while sustaining approximately the same pitch.

The two pneumogastric nerves are the right and left vagus nerves, the tenth cranial nerves: mixed sensory, branchial motor and parasympathetic pathways from the medulla oblongata to the neck, thorax and abdomen. A useful description separates their apparent origin at the surface of the brain from the origins and terminations of their component fibres.

Rootlets emerge in the groove behind the inferior olive, between the glossopharyngeal nerve above and the accessory rootlets below. Branchial motor fibres arise chiefly in the nucleus ambiguus; preganglionic parasympathetic fibres arise in the dorsal motor nucleus of the vagus and, particularly for cardiac control, the nucleus ambiguus. Visceral sensory fibres have their cell bodies chiefly in the inferior vagal ganglion and terminate centrally in the nucleus of the solitary tract; somatic sensory fibres associated with the superior vagal ganglion project to the spinal trigeminal nucleus. Consequently a sensory fibre is not accurately described as originating in a motor nucleus simply because its peripheral nerve emerges nearby.^[ref]

Each vagus nerve leaves the skull through the jugular foramen, with the glossopharyngeal nerve and accessory nerve. It bears the small superior vagal ganglion at the foramen and the larger inferior vagal ganglion below it. Connections include communications with adjacent cranial nerves and the cervical sympathetic nervous system. Traditional descriptions assign fibres joining the vagus nerve from the cranial part of the accessory nerve to the latter peripheral nerve; their modern classification is more nuanced and does not change the peripheral branches being described. In the neck the vagus nerve descends in the carotid sheath, behind and between the internal jugular vein and the internal, then common, carotid artery.

Its meningeal and auricular branches supply small sensory territories of the cranial covering and external ear. Pharyngeal branches contribute to the pharyngeal plexus, supplying much of the soft palate and pharynx; the stylopharyngeus muscle belongs to the glossopharyngeal nerve and the tensor veli palatini muscle to the mandibular division of the trigeminal nerve. The internal branch of the superior laryngeal nerve supplies sensation above the vocal folds; its external branch supplies the cricothyroid muscle. The recurrent laryngeal nerve supplies the other intrinsic laryngeal muscles and sensation below the vocal folds. The right recurrent laryngeal nerve loops beneath the right subclavian artery; the left loops under the aortic arch beside the ligamentum arteriosum. Both return towards the larynx near the groove between trachea and oesophagus.^[ref]

In the thorax, both vagus nerves pass behind the roots of the lungs, contrasting with the anterior course of the phrenic nerves. Cardiac branches join the cardiac plexus; pulmonary branches join the pulmonary plexus. The trunks break up into the oesophageal plexus, then collect principally as an anterior trunk derived from the left vagus nerve and a posterior trunk derived from the right. Through the oesophageal hiatus they reach the stomach; hepatic and coeliac branches distribute to abdominal viscera. Their parasympathetic territory includes foregut and midgut derivatives, extending into the proximal colon, rather than every abdominal and pelvic organ.^[ref] This extensive distribution explains why the level of experimental section is indispensable information.

The main consequences of section can be organized by the interrupted functions:

A discriminating historical experiment would record respiratory movements and heart rate before and after section, distinguish unilateral from bilateral section, and compare an intact airway with an airway bypass. A tracheal cannula can separate obstruction at the glottis from changes in the respiratory rhythm, while the central-versus-peripheral stimulation comparison separates incoming reflex traffic from outgoing motor effects. Later separate-lung recordings confirmed that a change following unilateral section could affect both lungs, supporting a central reflex interpretation rather than simple local paralysis.^[ref] The gastric distinction is also borne out by measurements of persistent acidity after surgical vagotomy, despite major reductions in stimulated gastric acid secretion.^[ref]

Inflammation of the pharynx.