By MRCSA in MRCS Part A — 04 Jul 2026

11 PARASYMPATHETIC PATHWAYS OF THE HEAD & NECK

# 12 PARASYMPATHETIC PATHWAYS OF THE HEAD & NECK

👩‍⚕️ Four parasympathetic pathways. Four ganglia. Four glandular (or smooth muscle) targets. Examiners love this topic because it forces you to track a fibre from brainstem nucleus, along a cranial nerve, through a named ganglion, and onto a final peripheral nerve. Learn the pattern once and the questions become almost automatic.

The general principle

All four pathways follow the same blueprint:

Preganglionic nucleus (brainstem) → preganglionic cranial nerve (CN III, VII, VII, or IX) → named branch → synapse in a parasympathetic ganglion → postganglionic fibres hitchhike on a trigeminal branch → target organ.

Three crucial points:

- Only CN III, VII and IX carry parasympathetic fibres to the head. The vagus (CN X) supplies the thorax and abdomen — not the head and neck glands.

- The ganglion is always parasympathetic, never sympathetic. Sympathetic fibres pass through these ganglia without synapsing (they synapsed in the superior cervical ganglion already).

- Postganglionic parasympathetic fibres are short and need a peripheral nerve to deliver them to the target — that delivery vehicle is almost always a branch of the trigeminal nerve (V).

The master table

Ganglion	Preganglionic CN	Brainstem nucleus	Preganglionic nerve	Postganglionic carrier (V branch)	Target	Function
Ciliary	CN III	Edinger-Westphal	Short branch to inferior oblique	Short ciliary nerves (via nasociliary, V1)	Sphincter pupillae + ciliary muscle	Pupil constriction + accommodation
Pterygopalatine	CN VII	Superior salivatory	Greater petrosal → joins deep petrosal to form nerve of pterygoid canal (Vidian)	Zygomatic branch of V2 → lacrimal branch of V1	Lacrimal gland (+ nasal and palatine glands)	Lacrimation, nasal secretion
Submandibular	CN VII	Superior salivatory	Chorda tympani → joins lingual nerve (V3)	Lingual nerve (V3)	Submandibular + sublingual glands	Salivation
Otic	CN IX	Inferior salivatory	Tympanic nerve (Jacobsen) → tympanic plexus → lesser petrosal (exits via foramen ovale)	Auriculotemporal nerve (V3)	Parotid gland	Salivation

👩‍⚕️ Pattern recognition: VII has two ganglia (pterygopalatine and submandibular), III and IX have one each. Whenever you see "lacrimation" or "submandibular/sublingual salivation" — think facial nerve. "Parotid" — glossopharyngeal. "Pupil" — oculomotor.

Ciliary ganglion (CN III)

Preganglionic fibres leave the Edinger-Westphal nucleus in the midbrain and travel within CN III. They enter the orbit via the superior orbital fissure, hop off the branch to inferior oblique, and synapse in the ciliary ganglion, which lies lateral to the optic nerve in the posterior orbit.

Postganglionic fibres run forward as the short ciliary nerves, pierce the sclera, and supply two smooth muscles:

- Sphincter pupillae — pupillary constriction (miosis)

- Ciliary muscle — contracts the ciliary body, slackens the suspensory ligaments, lens fattens, near focus → accommodation

➡ Examiner trap: the dilator pupillae is sympathetic (T1 via superior cervical ganglion → long ciliary nerves). Do not mix these up.

➡ Clinical: a third nerve palsy causes a fixed, dilated pupil because parasympathetic outflow is lost and sympathetic tone is unopposed. Pupillary fibres sit superficially on CN III, so compressive lesions (posterior communicating artery aneurysm, uncal herniation) blow the pupil before causing ophthalmoplegia.

Pterygopalatine ganglion (CN VII → lacrimal gland)

Preganglionic fibres arise in the superior salivatory nucleus (pons), travel with CN VII into the internal acoustic meatus, pass through the geniculate ganglion without synapsing, and emerge as the greater petrosal nerve. The greater petrosal crosses the foramen lacerum, joins the sympathetic deep petrosal nerve to form the nerve of the pterygoid canal (Vidian nerve), and reaches the pterygopalatine ganglion in the pterygopalatine fossa.

Postganglionic fibres take an unusual two-step route to the lacrimal gland:

1. Hitchhike on the zygomatic branch of V2

2. Jump across to the lacrimal branch of V1 via a communicating twig

3. Delivered to the lacrimal gland

Other postganglionic fibres supply mucous glands of the nose, palate and pharynx.

➡ Clinical: damage anywhere along this pathway (orbital floor fractures, skull-base tumours, pterygopalatine fossa surgery, parotid radiotherapy affecting CN VII upstream) → dry eye. "Crocodile tears" syndrome is aberrant regeneration after a Bell's palsy: salivary fibres misroute to the lacrimal gland, so the patient cries while eating.

Submandibular ganglion (CN VII → submandibular + sublingual glands)

Preganglionic fibres again leave the superior salivatory nucleus with CN VII. Inside the facial canal, they branch off as the chorda tympani. The chorda tympani crosses the medial surface of the tympanic membrane (between the malleus and incus), exits the skull via the petrotympanic fissure, and joins the lingual nerve (a branch of V3) in the infratemporal fossa.

The fibres travel within the lingual nerve until it descends near the submandibular gland, where they synapse in the submandibular ganglion (which hangs off the lingual nerve like a lantern).

Postganglionic fibres:

- Supply the submandibular gland directly

- Re-join the lingual nerve to reach the sublingual gland

👩‍⚕️ The chorda tympani also carries taste from the anterior two-thirds of the tongue. This is why a lingual nerve injury (e.g. during wisdom tooth extraction) produces ipsilateral loss of taste and reduced submandibular salivation.

Otic ganglion (CN IX → parotid gland)

Preganglionic fibres leave the inferior salivatory nucleus (medulla) in CN IX. They exit the skull through the jugular foramen, branch off as the tympanic nerve of Jacobsen, ascend back into the middle ear to form the tympanic plexus on the promontory, then emerge as the lesser petrosal nerve. The lesser petrosal exits the skull through the foramen ovale and synapses in the otic ganglion, just below the foramen ovale, medial to V3.

Postganglionic fibres hitchhike on the auriculotemporal nerve (V3) to reach the parotid gland.

➡ Frey's syndrome (gustatory sweating) is the auriculotemporal version of crocodile tears: after parotidectomy, regenerating parasympathetic fibres misroute onto sympathetic sweat-gland targets in overlying skin — patient sweats over the cheek while eating.

➡ Note the parotid gland is traversed by the facial nerve but not innervated by it. CN VII gives motor supply to muscles of facial expression only. Parotid secretomotor supply is CN IX.

[Image: Composite diagram of the four parasympathetic pathways of the head and neck, showing nuclei, cranial nerves, ganglia and target organs]

[Image: MCQs banner]

Test yourself

A patient suffers an orbital floor fracture and now has loss of lacrimation. Which nerve is most likely affected?

((Lacrimal nerve::Sensory branch of V1 only; carries postganglionic fibres but is not their source.))
((Facial CN VII::Too proximal — answer asks for the specific parasympathetic carrier, not the parent nerve.))
((Greater petrosal nerve::☑️ Carries preganglionic parasympathetics from CN VII to the pterygopalatine ganglion for lacrimation.))
((Auriculotemporal nerve::Carries postganglionic parasympathetics from the otic ganglion to the parotid, not the lacrimal gland.))

👩‍⚕️ Loss of lacrimation after orbital, skull-base or pterygopalatine fossa injury — think greater petrosal nerve and pterygopalatine ganglion.

A patient presents with loss of lacrimation. Which ganglion is involved?

((Otic::Relays CN IX fibres to the parotid gland via the auriculotemporal nerve.))
((Submandibular::Relays CN VII fibres (chorda tympani) to the submandibular and sublingual glands.))
((Pterygopalatine::☑️ Receives the greater petrosal nerve and relays parasympathetic fibres to the lacrimal gland via V2 → V1.))
((Ciliary::Relays CN III fibres to the sphincter pupillae and ciliary muscle — pupil constriction and accommodation.))

Which nerve delivers postganglionic parasympathetic fibres to the parotid gland?

((Lesser petrosal::This is the preganglionic nerve to the otic ganglion — not the postganglionic carrier.))
((Facial nerve::Traverses the parotid but supplies muscles of facial expression, not parotid secretion.))
((Greater petrosal::Preganglionic fibres to the pterygopalatine ganglion for lacrimation, not parotid.))
((Auriculotemporal nerve::☑️ Branch of V3 that carries postganglionic fibres from the otic ganglion to the parotid.))

👩‍⚕️ Classic Frey's syndrome question: gustatory sweating after parotidectomy is aberrant regeneration of auriculotemporal parasympathetic fibres.

After a wisdom tooth extraction, a patient develops loss of taste over the anterior two-thirds of the tongue and reduced salivation. Which nerve has been injured?

((Chorda tympani::Carries the same fibres but is injured proximally in the middle ear, not during dental work.))
((Lingual nerve::☑️ Carries chorda tympani fibres (taste + parasympathetic to submandibular ganglion) and is vulnerable during third molar extraction.))
((Glossopharyngeal nerve::Supplies taste and sensation to the posterior third of the tongue.))
((Hypoglossal nerve::Pure motor — tongue muscles only, no taste or secretomotor role.))

A patient with a third nerve palsy has a fixed, dilated pupil. Which fibres have been interrupted?

((Sympathetic fibres from T1::Sympathetic loss causes a constricted pupil (Horner's), not a dilated one.))
((Parasympathetic fibres from the Edinger-Westphal nucleus::☑️ Loss of parasympathetic outflow to sphincter pupillae leaves unopposed sympathetic dilatation.))
((Postganglionic fibres in the long ciliary nerves::Long ciliary nerves carry sympathetic fibres to the dilator pupillae.))
((Sensory fibres in the nasociliary nerve::Nasociliary is sensory to the cornea — affects the blink reflex, not pupil size.))

👩‍⚕️ Surgical sieve for a blown pupil: posterior communicating artery aneurysm or uncal herniation — pupillary fibres sit superficially on CN III and go first.

The lesser petrosal nerve exits the skull through which foramen?

((Foramen rotundum::Transmits V2 (maxillary nerve).))
((Foramen spinosum::Transmits the middle meningeal artery.))
((Foramen ovale::☑️ Transmits V3 and the lesser petrosal nerve; otic ganglion sits just below it.))
((Foramen lacerum::Crossed by the greater petrosal nerve, not transmitted through it.))

Revision summary

- Four ganglia, four targets: Ciliary → pupil/lens; Pterygopalatine → lacrimal; Submandibular → submandibular + sublingual; Otic → parotid.

- Cranial nerves: CN III (Edinger-Westphal) → ciliary. CN VII (superior salivatory) → pterygopalatine and submandibular. CN IX (inferior salivatory) → otic.

- Postganglionic carrier is always a trigeminal branch: V1 nasociliary (ciliary), V2 zygomatic → V1 lacrimal (pterygopalatine), V3 lingual (submandibular), V3 auriculotemporal (otic).

- Foramina: lesser petrosal exits foramen ovale; chorda tympani exits petrotympanic fissure; greater petrosal crosses foramen lacerum.

- Classic clinical hooks: orbital floor fracture → dry eye (pterygopalatine). Wisdom tooth extraction → lingual nerve (loss of taste + salivation). Parotidectomy → Frey's syndrome (auriculotemporal). PCom aneurysm → blown pupil (CN III parasympathetics).

- Pitfalls: vagus does not supply head and neck glands; dilator pupillae is sympathetic, not parasympathetic; CN VII traverses but does not secretomotor-supply the parotid.