Trigeminal nerve (CN V)

Nervus trigeminus

Also known as: CN V, fifth cranial nerve, V1 V2 V3

The largest cranial nerve and a mixed nerve. It is the main sensory nerve of the face, scalp, eye, nasal and oral cavities, teeth and most of the dura. Through its mandibular division it is also the motor nerve to the muscles of mastication (1st pharyngeal arch).

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Overview

Largest cranial nerveYes

GanglionTrigeminal (semilunar/Gasserian), in Meckel's cave

ForaminaSOF (V1), rotundum (V2), ovale (V3)

NucleiMesencephalic, principal sensory, spinal, motor

Pharyngeal arch1st (V3 motor)

CN V leaves the lateral pons as a large sensory root and a small motor root. The sensory root expands into the trigeminal (semilunar, Gasserian) ganglion, which lies in a dural pouch (Meckel's cave) over the petrous apex in the middle cranial fossa. This is the cranial equivalent of a dorsal root ganglion. From the ganglion arise three divisions:
• ophthalmic (V1), through the superior orbital fissure;
• maxillary (V2), through the foramen rotundum;
• mandibular (V3), through the foramen ovale, which carries the whole motor root.

V1 and V2 are purely sensory; V3 is mixed.

Four brainstem nuclei are involved:
• the mesencephalic nucleus (midbrain) for proprioception from the muscles of mastication; it contains the only primary sensory cell bodies inside the CNS;
• the principal (chief) sensory nucleus (pons) for discriminative touch;
• the spinal trigeminal nucleus (pons to C2) for pain and temperature;
• the motor nucleus (pons, SVE).

Trigeminal sensory fibres cross and ascend in the trigeminal lemniscus to the VPM nucleus of the thalamus. The divisions also act as "carriers" for autonomic fibres from other nerves, which hitch-hike through the parasympathetic ganglia:
• lacrimal secretomotor fibres (VII) via the zygomatic (V2) and lacrimal (V1) nerves;
• taste and submandibular fibres (VII, chorda tympani) via the lingual nerve (V3);
• parotid fibres (IX) via the auriculotemporal nerve (V3).

Location: Lateral pons → trigeminal ganglion in Meckel's cave (middle cranial fossa) → three divisions to the orbit, the pterygopalatine fossa and the infratemporal fossa.

Parts & subdivisions

Ophthalmic division (V1)
Sensory. Exits through the superior orbital fissure; branches are the lacrimal, frontal and nasociliary nerves. It is the afferent limb of the corneal reflex, via the long ciliary nerves of the nasociliary branch.
Maxillary division (V2)
Sensory. Exits through the foramen rotundum. In the pterygopalatine fossa it suspends the pterygopalatine ganglion (VII parasympathetic) and continues as the infraorbital nerve to the mid-face.
Mandibular division (V3)
Mixed. Exits through the foramen ovale. It supplies the muscles of mastication, and its sensory branches are the lingual, inferior alveolar, buccal and auriculotemporal nerves. The otic ganglion (IX) hangs from it. The jaw jerk uses V3 for both its afferent and efferent limbs.
Clinical testing
- Sensation: light touch and pinprick in each division (forehead, cheek, jaw), comparing sides. • Corneal reflex: touch the cornea with cotton wool; a bilateral blink is normal. • Motor: palpate the masseter and temporalis while the patient clenches; ask them to open the mouth against resistance. With a unilateral V3 lesion the jaw deviates toward the weak side, because the intact lateral pterygoid pushes the jaw across. • Jaw jerk.
Lesion signs
Ipsilateral facial sensory loss in a divisional pattern (peripheral lesion) or an "onion-skin" pattern (spinal trigeminal nucleus lesion). Other signs are a lost corneal reflex, wasting of the temporalis and masseter, and jaw deviation toward the lesion.

Anatomy

Innervation

- Sensory: the face (except the angle of the jaw, which is C2–C3 via the great auricular nerve), anterior scalp, cornea, conjunctiva, nasal and oral mucosa, teeth, anterior 2/3 of the tongue (general sensation), paranasal sinuses and the dura of the anterior and middle cranial fossae.
• Motor (V3): masseter, temporalis, medial and lateral pterygoids, mylohyoid, the anterior belly of digastric, tensor tympani and tensor veli palatini.

Nerve roots

Sensory root and motor root from the lateral pons (at the middle cerebellar peduncle).

Branches

V1 (ophthalmic), through the superior orbital fissure, divides into lacrimal, frontal (supraorbital and supratrochlear) and nasociliary nerves:
• Nasociliary gives long ciliary nerves to the cornea, the infratrochlear and ethmoidal nerves, and the external nasal nerve to the tip of the nose.
• Supplies: forehead and scalp to the vertex, upper eyelid, cornea and conjunctiva, dorsum of the nose, and the frontal and ethmoid sinuses.

V2 (maxillary), through the foramen rotundum to the pterygopalatine fossa:
• Branches: infraorbital nerve (through the infraorbital foramen), zygomatic nerve (zygomaticotemporal and zygomaticofacial branches), superior alveolar nerves (posterior, middle, anterior) to the upper teeth, and greater and lesser palatine and nasopalatine nerves.
• Supplies: lower eyelid, cheek, side of the nose, upper lip, upper teeth and gums, maxillary sinus, palate and nasal cavity.

V3 (mandibular), through the foramen ovale to the infratemporal fossa:
• Sensory branches: buccal nerve (cheek mucosa), auriculotemporal nerve (temple, auricle, TMJ), lingual nerve (general sensation to the anterior 2/3 of the tongue, floor of mouth), and inferior alveolar nerve (lower teeth; mental nerve to the chin and lower lip). The meningeal branch (nervus spinosus) returns through the foramen spinosum.
• Motor branches: the four muscles of mastication (masseter, temporalis, medial and lateral pterygoid), mylohyoid, the anterior belly of digastric, tensor tympani and tensor veli palatini.

Function

General sensation (touch, pain, temperature, proprioception) of the face, scalp, eye, nasal and oral cavities, teeth and dura
Mastication (muscles of the 1st pharyngeal arch)
Tensing the tympanic membrane and the soft palate
Afferent limb of the corneal, sneeze, lacrimal and jaw-jerk reflexes
Distributes parasympathetic (VII, IX) and taste (VII) fibres to their targets

Clinical significance

Trigeminal neuralgia (tic douloureux)

Paroxysms of severe, electric shock-like, unilateral facial pain lasting seconds, most often in V2 or V3. Attacks are triggered by light touch, chewing, talking or cold wind. Most cases are caused by neurovascular compression of the nerve root (usually by the superior cerebellar artery) near the pons. In a young patient or with bilateral pain, consider multiple sclerosis. First-line treatment is carbamazepine; refractory cases may undergo microvascular decompression.

Herpes zoster ophthalmicus

Reactivation of varicella-zoster virus in the trigeminal ganglion produces a painful vesicular rash in the V1 dermatome. Hutchinson sign (vesicles on the tip of the nose, supplied by the external nasal branch of the nasociliary nerve) predicts ocular involvement such as keratitis and uveitis. It needs urgent antivirals and ophthalmology review.

Dental anaesthesia

An inferior alveolar nerve block at the mandibular foramen anaesthetises the lower teeth, and also the lower lip and chin (mental nerve). It often anaesthetises the lingual nerve as well, giving numbness of the anterior tongue.

Mnemonics

Foramina of V1, V2, V3

"Standing Room Only": Superior orbital fissure, foramen Rotundum, foramen Ovale.

V3 motor targets

"Muscles of mastication + Mylohyoid, Anterior belly of digastric, Tensor tympani, Tensor veli palatini" ("MATT"). V3 supplies the two "tensors".

Compiled from standard anatomy and physiology references — see the Nervous System sources. For education only; not medical advice.