Parasympathetic Ganglia
The four parasympathetic ganglia of the head and neck are home to the cell bodies of the post-ganglionic parasympathetic nerves. Somatic and sympathetic nerves often traverse the parasympathetic ganglia but never synapse in them.
Ciliary Ganglion
The ciliary ganglion is located about 1 cm anterior to the superior orbital fissure at the apex of the orbit, and supplies parasympathetic input to the eyeball. It is found between the optic nerve and the lateral rectus. It has three roots – motor, sensory and sympathetic. Around eight short ciliary nerves arise from the ganglion and pierce the eyeball adjacent to the optic nerve. These fibres then pass along the internal surface of the sclera to the cornea, iris and ciliary body.
The motor root is a branch of the oculomotor nerve (III) which carries the pre-ganglionic parasympathetic fibres from the accessory nucleus of the oculomotor nerve. These nerves synapse in the ganglion. Parasympathetic nerves are motor to the sphincter pupillae and muscles of the ciliary body.
The sensory root arises from the nasociliary nerve, itself a branch of the ophthalmic nerve (V1). It conveys the sensory fibres from the cornea, ciliary body and iris.
The sympathetic root conveys a variable number of fibres. It arises as a thin nerve from the internal carotid plexus, with the post-ganglionic cell bodies lying in the superior cervical ganglion. It passes through the superior orbital fissure and enters the ciliary ganglion. Fibres traverse the ganglion without synapsing and are distributed via the short ciliary nerves. Sympathetic fibres innervate the dilator pupillae muscle of the iris as well as blood vessels within the eyeball. Some are distributed to the ciliary muscle.
Summary of Ciliary Ganglion
| Supply | Route | Function |
|---|---|---|
| Parasympathetic | Motor Root (via III) | Motor to sphincter pupillae and ciliary body |
| Sympathetic | Sympathetic Root (via Internal Carotid Plexus) | Motor to dilator pupillae |
| General Sensory | Sensory Root (via V1) | Sensory to cornea, iris, ciliary body |
Pterygopalatine Ganglion
The pterygopalatine ganglion is the largest of the four cranial parasympathetic ganglia. It is located anterior to the foramen rotundum and pterygoid canal, near to the sphenopalatine foramen and beneath the maxillary nerve.
The pterygopalatine has two roots. The sensory routes arise from the maxillary nerve as it passes through the pterygopalatine fossa. The nerve of the pterygoid canal, carrying sympathetic and parasympathetic fibres, enters the ganglion posteriorly.
Numerous nerves arise from the ganglion and are considered to be branches of the maxillary nerve.
- Orbital branches pass through the superior orbital fissure
- The nasopalatine nerve passes through the sphenopalatine foramen and runs along the nasal septum. It passes anteriorly and inferiorly and enters the oral cavity through the incisive foramen.
- Posterior superior nasal nerves also pass through the sphenopalatine foramen to supply the mucosa of the superior and posterior nasal cavity.
- The greater and lesser palatine nerves pass through the greater palatine canal and supply the mucosa of the hard and soft palate
- The pharyngeal branch of the maxillary nerve accompanies the pharyngeal branch of the maxillary artery, passing through the palatovaginal canal to supply mucosa of the nasopharynx posterior to the pharyngotympanic tube.
Pre-ganglionic parasympathetic fibres are sourced from the facial nerve. They travel in the greater petrosal nerve, which collects the deep petrosal nerve from the internal carotid plexus and becomes the nerve of the pterygoid canal. After synapsing in the ganglion, post-ganglionic fibres join the maxillary nerve via a ganglionic branch. These are distributed to the lacrimal gland via the zygomatic and zygomaticotemporal branches of the maxillary nerve. Other secretomotor fibres of unknown origin are also distributed to the mucosa associated with the maxillary nerve.
Post-ganglionic sympathetic fibres from the superior cervical ganglion initially pass through the internal carotid plexus before accumulating as the deep petrosal nerve. This combines with the greater petrosal nerve to form the nerve of the pterygoid canal. Sympathetic fibres do not synapse in the pterygopalatine fossa and are distributed along the branches of the maxillary nerve.
Summary of Pterygopalatine Ganglion
| Supply | Route | Function |
|---|---|---|
| Parasympathetic | Nerve of the pterygoid canal (via greater petrosal nerve, VII) | Secretomotor to lacrimal gland, mucous glands of posterior/superior nasal cavity, nasopharynx, hard and soft palate. |
| Sympathetic | Nerve of the pterygoid canal (via internal carotid plexus) | Smooth muscle control of head and neck vessels. Lacrimal branches with uncertain function |
| General Sensory | Sensory Root (via V2) | Sensory to mucosa of posterior nasopharynx, posterior and superior nasal cavity, hard and soft palate |
Otic Ganglion
The otic ganglion is located in the infratemporal fossa, just below the foramen ovale. It is closely associated with the mandibular nerve (V3). It has a motor and sympathetic root. The sensory root is not well defined.
Pre-ganglionic parasympathetic motor fibres originate in the inferior salivatory nucleus and leave the brainstem with the glossopharyngeal nerve (IX). They leave with the tympanic nerve within the jugular foramen, and pass through the temporal bone to reach the middle ear, forming the tympanic plexus. The lesser petrosal nerve arises from this plexus, and emerges into the middle cranial fossa. It exits the foramen ovale with the mandibular nerve to reach the otic ganglion, synapsing with post-ganglionic fibres. The fibres leave the otic ganglion through a communicating branch to the auriculotemporal nerve, and thereby reach the parotid gland where they stimulate salivation.
Sympathetic fibres arise as a small nerve from a plexus surrounding the middle meningeal artery. The fibres pass through the ganglion without synapsing and accompany parasympathetic fibres to the parotid, where they act upon the vessels.
Summary of Otic Ganglion
| Supply | Route | Function |
|---|---|---|
| Parasympathetic | Lesser petrosal nerve (via tympanic nerve, IX) | Secretomotor to parotid gland |
| Sympathetic | Branch from middle meningeal plexus | To vessels within parotid gland |
Submandibular Ganglion
The submandibular ganglion is located on the hyoglossus muscle. It has the three roots of a parasympathetic ganglion.
Pre-ganglionic fibres are derived from the superior salivatory nucleus. They exit the posterior cranial fossa with the facial nerve, before departing as the chorda tympani nerve. This nerve arises 6 mm above the stylomastoid foramen, passing through a canal in the temporal bone to emerge into the middle ear via the posterior canaliculus. It curves through the middle ear, along the superior aspect of the tympanic membrane, and departs through the anterior canaliculus. The chorda tympani exits the skull via the petrotympanic fissure and unites with the lingual nerve in the infratemporal fossa. It then accompanies this nerve before leaving to become the motor root of the submandibular ganglion, in which the pre-ganglionic fibres synapse. Post ganglionic secretomotor fibres are distributed to the submandibular gland. Post-ganglionic fibres to the sublingual gland exit separately and rejoin the lingual nerve to reach their destination.
The sympathetic root arises from a plexus surrounding the facial artery. They are vasomotor to the vessels of the submandibular and sublingual salivary glands.
The sensory root arises from the lingual nerve. Its exact function is not well specified - ?general sensory to the submandibular gland.
Summary of Submandibular Ganglion
| Supply | Route | Function |
|---|---|---|
| Parasympathetic | Motor root from lingual nerve (via chorda tympani, VII) | Secretomotor to submandibular / sublingual salivary glands |
| Sympathetic | Branch from facial artery plexus | Vasomotor to submandibular / sublingual salivary glands |
| General Sensory | Sensory Root (via lingual nerve, V3) | ?? general sensory to submandibular gland |
Sympathetic Ganglia
Unlike the parasympathetic nerves of the head and neck, the sympathetic nerves exit the central nervous system from the thoracic spinal cord. They must therefore ascend back into the head and neck region to exert their influence. The cell bodies of post ganglionic sympathetic fibres are located in three ganglia within the neck.
Superior Cervical Ganglion
The superior cervical ganglion is the largest of the three neck ganglia. It is located posterior to the carotid artery and anterior to longus capitis. It connects inferiorly with the middle cervical ganglion. Its largest branch is the internal carotid nerve, which unites with the artery and forms a plexus within the cavernous sinus. This branch is responsible for sympathetic innervation to the eyeball (via the sympathetic root of the ciliary ganglion) as well as numerous glands associated with the maxillary nerve (lacrimal, nasal cavity, palate).
Lateral branches unite with the cervical nerves 1 – 4. Some also ascend with the internal jugular vein and merge with the glossopharyngeal and vagus nerves. Another branch unites with the hypoglossal nerve.
Medial branches are either laryngopharyngeal or cardiac. Laryngopharyngeal branches supply the carotid body and then merge with the fibres of cranial nerves IX and X to form the pharyngeal plexus. Cardiac branches descend along the posterior surface of the common carotid artery, receiving branches from the middle and inferior plexuses, before merging with the cardiac plexus. These fibres are thought to be efferent only.
Anterior branches ascend with the external carotid artery, and form a plexus around it and its own branches. The plexus around the facial artery contributes the sympathetic root to the submandibular plexus, functioning as vasomotor supply to the submandibular and sublingual salivary glands. The plexus around the maxillary artery extends into the middle meningeal artery, and contributes the sympathetic root to the otic ganglion. The anterior branches are responsible for innervation of the sweat glands of the face.
Summary of Superior Cervical Ganglion
| Branch | Function |
|---|---|
| Internal Carotid | Forms internal carotid plexus, contributes supply to ciliary and pterygopalatine ganglia and vessels of brain |
| Lateral Branches | Unite with cervical nerves, cranial nerves IX, X and XII and distributed to their territories |
| Medial Branches | Laryngopharyngeal branches to carotid body and pharynx. Cardiac branches descend to the heart |
| Anterior Branches | Forms external carotid plexus, contributes sympathetic supply to otic and submandibular ganglia. Controls sweat glands of the face. |
Middle Cervical Ganglion
The middle cervical ganglion is also the smallest, and lies at about the level of C5-6. It has communications with the spinal nerves of C5 and C6, and also sends anterior branches to the thyroid gland. It has its own cardiac branch which descends to the cardiac plexus.
Inferior Cervical Ganglion
Larger than the middle, this ganglion lies at the level of C7. It may be continuous with the first thoracic ganglion. Like the middle, it has gray rami communicans to spinal nerves (in this case C7 and C8). It also possesses its own cardiac branch.
