In this note, we are going to discuss the anatomy and function of the trigeminal nerve (n. trigeminus), which is the CN V.

This nerve is responsible for several functions: it provides sensory innervation to the face, oral cavity, nasal cavity, and dura mater. It also provides motor innervation to the muscles of mastication.

According to the generally accepted classification of functional components, it contains the following fiber types:

• general somatic afferent fibers (GSA)
• special visceral efferent (SVE) or branchiomotor fibers

Therefore, the trigeminal nerve is a mixed nerve.

The motor nucleus of the trigeminal nerve (nucleus motorius nervi trigemini), which is located in the dorsolateral part of the pons, is the source of the motor fibers.

It receives impulses from the corticobulbar tract (fibrae corticonucleares), which originates in the contralateral precentral gyrus.

The sensory trigeminal ganglion (ganglion trigeminale),

which is located in the trigeminal impression (impressio trigemini) on the anterior surface of the petrous part of the temporal bone, is the source of the sensory fibers. It is also known as the Gasserian ganglion.

The peripheral processes of sensory neurons pass to the innervation areas forming three branches:

• the ophthalmic nerve CN V1 (n. ophthalmicus),

• the maxillary nerve CN V2 (n. maxillaris),

• and the mandibular nerve CN V3 (n. mandibularis)

The central processes of the sensory neurons enter the brain, where they divide into smaller ascending and descending bundles. The descending bundle forms the so-called spinal tract of the trigeminal nerve (tractus spinalis nervi trigemini).

Descending into the medulla, and then into the spinal cord, this tract becomes gradually thinner as its fibers synapse with the neurons of the spinal nucleus (nucl. spinalis nervi trigemini).

The ascending bundle passes to two other nuclei: the main (or principal) sensory nucleus (nucl. principalis nervi trigemini),

located in the dorsal part of the pons near the motor nucleus, and the mesencephalic nucleus (nucl. mesencephalicus nervi trigemini), located in the tegmentum of the midbrain (within the lateral periaqueductal grey matter).

The spinal nucleus receives pain and temperature information from the face, the main sensory nucleus receives tactile information from the face and mouth. And finally, the mesencephalic nucleus receives proprioception for masticatory muscles, and it also senses deep pressure which helps us to regulate the process of mastication.

Moreover, the sensory nuclei of the trigeminal nerve (mainly the spinal nucleus) receive information from other mixed cranial nerves: facial, glossopharyngeal and vagus.

After synapsing, the ascending fibers emerge from the sensory nuclei. This pathway is called trigeminal lemniscus (lemniscus trigeminalis). They run towards the thalamus, and from there to the cortex of the postcentral gyrus, where sensory information is processed.

The trigeminal nerve emerges from the lateral aspect of the pons by a large sensory root (radix sensoria)

and a smaller motor root (radix motoria).

In the cranial cavity, the nerve is located between the sheaths of the dura mater within the lateral wall of the cavernous sinus.

The nerve splits into three major branches, which exit the cranium.

• The ophthalmic nerve passes through the superior orbital fissure (fissura orbitalis superior).

• The maxillary nerve passes through the foramen rotundum (foramen rotundum).

• And the mandibular nerve leaves the cranium through the foramen ovale (foramen ovale).

Let’s discuss each of the major divisions of the trigeminal nerve in greater detail.

Ophthalmic nerve

Ophthalmic nerve (n. ophthalmicus, CN V1)

It emerges from the trigeminal ganglion.

The nerve passes along the lateral wall of the cavernous sinus. It gives off the recurrent tentorial nerve, which courses backward and innervates the tentorium cerebelli.

The ophthalmic nerve exits the cranium through the superior orbital fissure and enters the orbit after dividing into the following branches:

• The lacrimal nerve (n. lacrimalis), which is located near the external surface of the orbit. It innervates the skin and conjunctiva of the external part of the superior eyelid and provides sensory innervation to the lacrimal gland. It also contains postganglionic parasympathetic fibers from the pterygopalatine ganglion.

• The frontal nerve (n. frontalis), which courses forwards, directly beneath the roof of the orbit and superiorly to the superior palpebral levator muscle. A little before reaching the supraorbital margin, it divides into two terminal branches: the supraorbital and supratrochlear branches.

• The supraorbital nerve (n. supraorbitalis), which passes through the supraorbital notch (or foramen) and supplies the conjunctiva and the skin of the upper eyelid, the skin of the lower forehead, and the mucous membrane of the frontal sinus.

• The supratrochlear nerve (n. supratrochlearis), which passes above the trochlea and circumflexes the superior orbital margin interiorly to the supraorbital nerve

and innervates the skin of the dorsum of the nose and adjacent skin of the upper eyelid.

• The nasociliary nerve (n. nasociliaris),

which passes forward along the superior border of the medial rectus muscle, giving off the following branches:

1. The communicating branch for the ciliary ganglion (r. communicans).

Through this branch, the sensory fibers that were passing from the eyeball as part of the short ciliary nerves leave the ganglion and then pass further as part of the nasociliary nerve. Moreover, short ciliary nerves contain postganglionic parasympathetic fibers from the Edinger-Westphal nucleus, innervating the ciliary body and the sphincter pupillae muscle.

2. Long ciliary nerves (nn. ciliares longi) penetrate the posterior part of the sclera, innervating the sclera and the choroidea.

3. The posterior ethmoid nerve (n. ethmoidalis posterior)

passes through the posterior ethmoid foramen and innervates the ethmoid cells and sphenoid sinus.

4. The infratrochlear nerve (n. infratrochlearis) exits the orbit below the trochlea of the superior oblique muscle and innervates the skin and conjunctiva of the upper eyelid, as well as the skin of the nasal root.

5. The anterior ethmoid nerve (n. ethmoidalis anterior)

passes through the anterior ethmoid foramen and enters the anterior cranial fossa,

where it lies on the superior surface of the horizontal plate of the ethmoid bone. From here, it passes into the nasal cavity through the small hiatus located laterally to the crista galli. This nerve innervates the mucous membrane of the nasal cavity.

The direct continuation of the anterior ethmoid nerve is the external nasal nerve (r. nasalis externus), which exits the nasal cavity between the nasal bone and the superior nasal cartilage and innervates the skin of the nose.

Maxillary nerve

Maxillary nerve (n. maxillaris, CN V2)

It emerges from the trigeminal ganglion.

The maxillary nerve passes along the lateral wall of the cavernous sinus, exits the cranium,

and enters the pterygopalatine fossa.

From there, the nerve goes into the orbit through the inferior orbital fissure,

and continues as the infraorbital nerve (n. infraorbitalis).

The infraorbital nerve lies in the infraorbital sulcus

and then enters the eponymous canal until it eventually passes through the infraorbital foramen.

In the area of the infraorbital sulcus, the nerve passes close to the maxillary sinus. Here it gives off the following branches:

• Anterior superior alveolar branches (rr. alveolares superiores anteriores)

• Middle superior alveolar branch (r. alveolaris superior medius)

• Together with the posterior superior alveolar branches, they form the superior dental plexus, which innervates the maxillary sinus and maxillary teeth.

Exiting the canal, the nerve divides into multiple small branches.

These are:

• External nasal branches (rr. nasales externi), these innervate the skin of the nose

• Internal nasal branches (rr. nasales interni), which innervate the nasal septum
• Superior labial branches (rr. labiales superiores), which innervate the upper lip

Inferior palpebral branches (rr. palpebrales inferiores), which innervate the lower eyelid

Along its course, the maxillary nerve gives off several more branches:

• The meningeal branch (r. meningeus), which innervates the dura mater of the middle cranial fossa.

• Branches to the pterygopalatine ganglion (rr. ganglionares).

They contain the sensory fibers that pass from the nasal cavity, palate, and pharynx through the ganglion without synapsing, and join the maxillary nerve.

• Posterior superior alveolar nerves (nn. alveolares superiores posteriores), which go to the maxillary tuberosity from the pterygopalatine fossa and through the alveolar foramina pass into the canals located inside the bone. With the other teeth branches, they form a plexus that innervates the teeth of the maxilla and the maxillary sinus.

• The zygomatic nerve (n. zygomaticus), which enters the orbit through the inferior orbital fissure and then goes superiorly along the lateral wall of the orbit, dividing into two branches.

The zygomaticofacial branch (r. zygomaticofacialis) is one of these terminal branches.

It passes to the face through the zygomaticofacial foramen, innervating the skin of the zygomatic region.

• The zygomaticotemporal branch (r. zygomaticotemporalis) is another terminal branch,

which emerges in the temporal region through the zygomaticotemporal foramen

on the posterior surface of the zygomatic bone, supplying the skin of the temporal region.

Furthermore, the zygomatic nerve contains postganglionic parasympathetic fibers from the pterygopalatine ganglion, which innervate the lacrimal gland.

• Lateral superior posterior nasal branches / LSPN (rr. nasales posteriores superiores laterales)

and medial superior posterior nasal branches / MSPN (rr. nasales posteriores superiores mediales)

pass through the sphenopalatine foramen and innervate the mucous membrane of the nasal cavity and paranasal sinuses. They also contain postganglionic parasympathetic fibers from the pterygopalatine ganglion, innervating the nasal glands.

The longest branch of the medial group is called the nasopalatine nerve (n. nasopalatinus).

It enters the incisive canal (canalis incisivus).

• The greater palatine nerve (n. palatinus major)

and usually two lesser palatine nerves (nn. palatini minores).

The greater nerve passes through the greater palatine canal (canalis palatinus major) and goes to the incisive fossa.

It innervates the mucous membrane of the hard palate. The lesser nerves pass, respectively, in the lesser palatine canals (canales palatini minores) and innervate the soft palate. Palatine nerves also contain postganglionic parasympathetic fibers from the pterygopalatine ganglion, innervating the minor salivary glands.

Mandibular nerve

Mandibular nerve (n. mandibularis, CN V3)

This branch of the trigeminal nerve is mixed. The motor component innervates the muscles developing from the first pharyngeal arch.

The sensory and motor roots of the mandibular nerve exit the cranial cavity through the foramen ovale and merge into the common trunk that descends between the lateral pterygoid muscle externally and the tensor veli palatini muscle internally.

There are two branches that arise from this common trunk.

1. The meningeal branch (r. meningeus), re-enters the cranium through the foramen spinosum and innervates the dura mater of the middle cranial fossa.

2. The medial pterygoid nerve (n. pterуgoideus medialis), which innervates the respective muscle.

Two branches arise from this nerve:

the nerve to the tensor veli palatini muscle (n. musculi tensoris veli palatini)

and the nerve to the tensor tympani muscle (n. musculi tensoris tympani).

Then mandibular nerve is divided into a smaller anterior and a larger posterior division.

Three motor branches and one sensory branch arise from the anterior division:

1. The masseteric nerve (n. massetericus)

which goes externally, passes through the mandibular notch to the internal surface of the masseter muscle and innervates it.

2. The deep temporal nerves (anterior and posterior) (nn. temporales profundi), which go superiorly to the internal surface of the temporalis muscle, innervating it.

3. The lateral pterygoid nerve (n. pterygoideus lateralis), which innervates the respective muscle.

4. The buccal nerve (n. buccalis), which is the sensory branch. It courses between the heads of the lateral pterygoid muscle.

It anastomoses with the buccal branches of the facial nerve (CN VII) and innervates the skin of the cheek and buccal mucosa.

There are two sensory branches and one mixed branch arising from the posterior division of the mandibular nerve.

1. The auriculotemporal nerve (n. auriculotemporalis), which loops around the middle meningeal artery.

It innervates the skin of the auricle and external acoustic meatus, the external surface of the tympanic membrane, and the skin of the temporal region above the auricle, as well as the temporomandibular joint. It also provides sensory innervation to the parotid gland. Moreover, a certain number of preganglionic parasympathetic fibers pass along the nerve to the otic ganglion.

2. The lingual nerve (n. lingualis), which descends along the external surface of the medial pterygoid muscle and then goes inferiorly along the internal surface of the mandible, passing beneath the submandibular gland and reaching the inferior surface of the tongue.

Dividing into terminal branches, it provides sensory innervation of the anterior two-thirds of the tongue, floor of the oral cavity and mandibular gingiva.

The chorda tympani, which is a branch of the facial nerve, joins it at the inferior border of the lateral pterygoid muscle. It provides gustatory innervation of the anterior two-thirds of the tongue.

3. The inferior alveolar nerve (n. alveolaris inferior), which is a mixed branch.

It enters the mandibular canal,

where it gives off numerous branches forming the inferior dental plexus.

The mental nerve (n. mentalis),

which is its terminal branch, exits the mandibular canal through the mental foramen

and innervates the skin of the lower lip and the chin.

At the entrance to the mandibular branch, it gives off the mylohyoid nerve (n. mylohyoideus), which is the motor branch that innervates the respective muscle

and gives off nerve fibers to the anterior belly of the digastric muscle.

Dictionary

CN V: Trigeminal nerve

Trigeminal nerve

nervus trigeminus

Sensory root

radix sensoria

Motor root

radix motoria

Trigeminal ganglion

ganglion trigeminale

Principal sensory nucleus of the trigeminal nerve

nucleus principalis n. trigemini

Pontine nucleus

nucleus pontinus n. trigemini

Spinal trigeminal nuclei

nucleus spinalis n. trigemini

Ophthalmic nerve

nervus ophthalmicus

Maxillary nerve

nervus maxillaris

Mandibular nerve

nervus mandibularis

Tentorial branch

ramus tentorius

Lacrimal nerve

nervus lacrimalis

Frontal nerve

nervus frontalis

Supraorbital nerve

nervus supraorbitalis

Supratrochlear nerve

nervus supratrochlearis

Nasociliary nerve

nervus nasociliaris

Anterior and posterior ethmoidal nerves

nn. ethmoidales anterior et posterior

Long ciliary nerves

nn. ciliares longi

Infratrochlear nerve

nervus infratrochlearis

Communicating branch to the ciliary ganglion

ramus communicans cum ganglio ciliare

Ciliary ganglion

ganglion ciliare

Ciliary nerves

nn. ciliares longi

Maxillary nerve

nervus maxillaris

Middle meningeal branch

ramus meningeus medius

Infraorbital nerve

nervus infraorbitalis

Inferior palpebral branches

rr. palpebrales inferiores

External nasal branches

rr. nasales externi

Superior labial branches

rr. labiales superiores

Superior alveolar nerves

nn. alveolares superiores

Anterior, middle, and posterior superior alveolar branches

rr. alveolares superiores anteriores, medius et posteriores

Superior dental plexus

plexus dentalis superior

Superior dental branches

rr. dentales superiores

Superior gingival branches

rr. gingivales superiores

Internal nasal branches

rr. nasales interni

Zygomatic nerve

n. zуgomaticus

Zygomaticotemporal branch

r. zуgomaticotemporalis

Zygomaticofacial branch

r. zуgomaticofacialis

Ganglionic branches to the pterygopalatine ganglion

rr. ganglionares ad ganglion pterуgopalatini

Pterygopalatine ganglion

ganglion pterуgopalatinum

Medial and lateral superior posterior nasal branches

rr. nasales posteriores superiores mediales et laterales

Nasopalatine nerve

n. nasopalatinus

Greater palatine nerve

n. palatinus major

Lesser palatine nerves

nn. palatini minores

Inferior posterior nasal branches

rr. nasales posteriores inferiores

Mandibular nerve

n. mandibularis

Masseteric nerve

n. massetericus

Deep temporal nerves

nn. temporales profundi

Nerves to lateral and medial pterygoid muscles

nn. pterуgoidei lateralis et medialis

Nerve of the tensor veli palatini muscle

n. musculi tensoris veli palatini

Nerve of the tensor tympani

nervus musculi tensoris

muscle

tуmpani

Buccal nerve

n. buccalis

Auriculotemporal nerve

n. auriculotemporalis

Lingual nerve

n. lingualis

Inferior alveolar nerve

n. alveolaris inferior

Meningeal branch

r. meningeus

Anterior auricular nerves

nn. auriculares anteriores

Nerve to external acoustic meatus

n. meatus acustici externi

Branches of the tympanic membrane

rr. membranae tуmpani

Superficial temporal branches

rr. temporales superficiales

Parotid branches

rr. parotidei

Otic ganglion

ganglion oticum

Lingual branches

rr. linguales

Sublingual nerve

n. sublingualis

Branches to the isthmus of the fauces

rr. isthmi faucium

Ganglionic branches to the sublingual ganglion and the submandibular ganglion

rr. ganglionares ad ganglion sublinguale et ad ganglion submandibulare

Sublingual ganglion

ganglion sublinguale

Communicating branch with chorda tympani

ramus communicans cum chorda tуmpani

Mental nerve

n. mentalis

Nerve to the mylohyoid

n. mуlohуoideus

Inferior dental plexus

plexus dentalis inferior

Inferior dental branches

rr. dentales inferiores

Inferior gingival branches

rr. gingivales inferiores

Inferior labial branches

rr. labiales inferiores