Trigeminal Nerve Anatomy and Function

• The trigeminal nerve is the largest cranial nerve.
• It exits the anterior pons as a small motor root and a large sensory root.
• This nerve passes forward from the posterior cranial fossa to the apex of the petrous temporal bone in the middle cranial fossa.

Trigeminal Ganglion

• The large sensory root forms the trigeminal ganglion.
• This ganglion is flattened and crescent-shaped.
• The trigeminal ganglion lies within the trigeminal cave (Meckel cave), a dural pouch lateral to the cavernous sinus.
• The motor root of the trigeminal nerve is below the sensory ganglion and separate.
• The ophthalmic (V1), maxillary (V2), and mandibular (V3) nerves originate from the ganglion's anterior border.

Functions of Trigeminal Nerve

• Somatic sensory (general) and somatic motor (branchial) to derivatives of the 1st pharyngeal arch.
• Nuclei include 4 trigeminal nuclei: one motor (motor nucleus of trigeminal nerve) and 3 sensory (mesencephalic, principal sensory, and spinal nuclei of trigeminal nerve).

Ophthalmic Nerve (V1)

• V1 is purely sensory.
• It runs forward in the lateral wall of the cavernous sinus in the middle cranial fossa.
• V1 enters the orbital cavity through the superior orbital fissure, then divides into three branches: lacrimal, frontal, and nasociliary nerves.

Lacrimal Nerve (Branch of V1)

• It joins the zygomaticotemporal branch of the maxillary nerve.
• The zygomaticotemporal branch contains parasympathetic secretomotor fibers for the lacrimal gland.
• The lacrimal nerve then enters the lacrimal gland.
• It provides branches to the conjunctiva and upper eyelid skin

Frontal Nerve (Branch of V1)

• The Frontal nerve runs forward on the upper levator palpebrae superioris surface.
• It divides into the supraorbital and supratrochlear nerves.
• These nerves exit the orbital cavity.
• They supply the frontal air sinus, forehead skin, and scalp.

Nasociliary Nerve (Branch of V1)

• Nasociliary nerve crosses the optic nerve.
• It proceeds forward on the upper medial rectus border.
• This nerve continues as the anterior ethmoid nerve.
• The anterior ethmoid nerve descends on the crista galli’s side to the nasal cavity.
• It gives off 2 internal nasal branches and supplies the tip of the nose's skin with the external nasal nerve.

Branches of Nasociliary Nerve

• The branches include the sensory fibers to the ciliary ganglion.
• The long ciliary nerves contain sympathetic fibers to the dilator pupillae muscle plus sensory fibers to the cornea.
• The infratrochlear nerve supplies eyelid skin.
• The external nasal nerve serves the dorsum skin up to the tip of the nose.
• The anterior and posterior ethmoidal nerve are sensory to the ethmoid and sphenoid sinuses.

Testing Ophthalmic Nerve Function

• The integrity is tested by checking the corneal reflex.
• Touching the cornea, also supplied by CN V1, with cotton evokes a reflexive blink if the nerve is functional.

Maxillary Nerve (V2)

• The maxillary nerve also arises from the trigeminal ganglion in the middle cranial fossa.

• It is purely sensory.

• The Maxillary Nerve passes forward in the lateral wall of the cavernous sinus.

• It exits the skull through the foramen rotundum.

• Maxillary Nerve transverses the pterygopalatine fossa.

• It reaches the orbit via the inferior orbital fissure.

• The Maxillary Nerve continues as the infraorbital nerve in the infraorbital groove.

• It emerges on the face through the infraorbital foramen.

• This nerve provides sensory fibers to the skin of the face and side of nose.

Branches of Maxillary Nerve (V2)

• Meningeal branches: supply the dura mater in the anterior middle cranial fossa, accompanying middle meningeal vessels and entering the cranium through the foramen spinosum.
• Zygomatic branch divides into zygomaticotemporal and zygomaticofacial nerves, which supply the face skin. The Zygomaticotemporal branch contains parasympathetic secretomotor fibers to lacrimal glands via the lacrimal nerve.
• Ganglionic branches: two short nerves that suspend the pterygopalatine ganglion in the pterygopalatine fossa.
• Posterior superior alveolar nerve: supplies maxillary sinus, upper molar teeth, and adjacent gum/cheek parts.
• Middle superior alveolar nerve: supplies maxillary sinus, upper premolar teeth, gums, and cheek.
• Anterior superior alveolar nerve: supplies maxillary sinus, plus the upper canine and incisor teeth.

Pterygopalatine Ganglion

• It is a parasympathetic ganglion suspended from the maxillary nerve in the pterygopalatine fossa and is secretomotor to the lacrimal and nasal glands.

• Contains sensory fibers that have passed through the ganglion coming from nose, palate & pharynx.

• They also contain postganglionic parasympathetic fibers going to the lacrimal gland.

• The parasympathetic fibers to the pterygopalatine ganglion come from the facial nerve via the greater petrosal nerve.

• The greater petrosal nerve joins the deep petrosal nerve as it passes through the foramen lacerum, forming the nerve of the pterygoid canal (Vidian Nerve), which then passes anteriorly through to the pterygopalatine fossa.

• The deep petrosal nerve is a sympathetic nerve from the internal carotid plexus as it exits the carotid canal.

• The nerve transmits postsynaptic fibers from nerve cell bodies in the superior cervical sympathetic ganglion to the pterygopalatine ganglion by joining the nerve of the pterygoid canal.

Postsynaptic Fibers

• The postsynaptic parasympathetic and sympathetic fibers pass to the lacrimal gland, palatine glands, and the mucosal glands of the nasal cavity and superior pharynx.
• These fibers do not synapse in the ganglion, but runs directly through the branches of CN V2.

Branches of the Pterygopalatine Ganglion:

• Orbital branches go the orbit through the inferior orbital fissure.
• Greater and lesser palatine nerves: supply the palate, tonsil and the nasal cavity.
• Pharyngeal branch: supplies the roof of the nasopharynx.
• Posterior (superior & inferior) lateral nasal nerves
• The nasopalatine nerve.

Trigeminal Neuralgia

• A relatively common condition with excruciating pain in the mandibular or maxillary division, with the ophthalmic division usually spared.
• Usually caused by pressure on the trigeminal nerve near the brain stem from artery or vein.
• Microvascular Decompression (MVD) Surgery: the most long-lasting treatment for trigeminal neuralgia vessel compression.

Overview of the trigeminal nerve, the largest cranial nerve, including its sensory and motor roots. Discusses the Trigeminal Ganglion, its location in the trigeminal cave, and the origin of the ophthalmic, maxillary, and mandibular nerves. Also covers the nerve's somatic sensory and motor functions.