The Fifth Cranial Nerves “The Trigeminal” By Prof. Dr. Muhammad Imran Qureshi

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The Fifth Cranial Nerves
“The Trigeminal”


Prof. Dr. Muhammad Imran Qureshi

The Trigeminal nerve has both Somatic Sensory and Branchial / Visceral Motor components.

It leaves the brainstem in two separate bundles.

One bundle contains all the Sensory axons (the Sensory root). It is the larger of the two. The other contains all the Motor axons (the Motor root).

After leaving the brain, the two roots travel alongside each other {with the motor root deep (medial) to the sensory root} toward the superior edge of the petrous temporal bone near its apex. Just below the superior petrosal sinus, they come across the arachnoid lying on the dura and push both meningeal layers out to form a two-layered pocket of these meninges. This meningeal pocket incorporates itself between the endocranium and dura on the anterior surface of the petrous temporal (at the site known as the trigeminal impression). This pocket is called Meckel's cave (or cavum trigeminale). Within the Meckel's cave, it is lies in subarachnoid space.

The sensory cell bodies of the Trigeminal nerve are located in a clump along the sensory root at the site where this root actually pierces the arachnoid / dural floor of Meckel's cave to take up a position between true dura and endocranium. This clump is crescentic in shape and is often called the Semilunar / Gasserian ganglion.scan0032.jpg

The peripheral processes of the sensory axons emerge from the anteroinferior edge of the ganglion in three separate bundles.

These three bundles are the Ophthalmic, Maxillary, and Mandibular divisions of the Trigeminal.

These are usually written as Va, Vb, and Vc or VI, VII, and VIII respectively.

The motor root also pierces the floor of Meckel's cave. It then joins the Mandibular division.

The Ophthalmic Nerve - Va or VI

The Ophthalmic nerve passes straight forward into the Cavernous sinus. Like the Oculomotor and Trochlear nerves, VI runs forward in the sinus with its epineurium adherent to the medial face of its lateral dural wall. It is the largest and most inferior of the three nerves adherent to the lateral dural wall of the Cavernous sinus. scan0042.jpg

While traveling within the sinus, it picks up postganglionic sympathetic fibers from the internal carotid plexus (these probably pass through the Abducent to reach it).

The sympathetic axons are distributed with branches of the ophthalmic nerve to supply vasculature of the orbit and forehead, sweat glands of the forehead, and the Dilator Pupillae. f66122-008-f044

After it exits the front of the cavernous sinus, it divides into its three main branches viz. the Frontal, the Lacrimal, and Nasociliary nerves.

These pass separately through the superior orbital fissure, the Frontal and Lacrimal in the upper compartment and the Nasociliary in the middle compartment of the SOF.

The Frontal nerve continues forward in the orbit onto the upper surface of Levator Palpebrae Superioris, and follows it toward the front of the eye.scan0033.jpg

Before reaching the orbital septum, the Frontal nerve bifurcates into a Supratrochlear and a Supraorbital branch.

The Supratrochlear is the smaller and medial of the two. Both of them pierce the orbital septum and turn upward into the superficial fascia of the scalp deep to the Frontalis muscle.

The Supraorbital nerve passes through the Supraorbital notch, where it is separated from the more inferiorly placed Supraorbital artery by a ligament (sometimes ossified) that bridges across the notch. The Supratrochlear nerve crosses the orbital rim at its upper inner angle. Both the Supraorbital and Supratrochlear are cutaneous nerves for the skin of the forehead all the way up to the vertex of the skull.

They also give twigs to the upper eyelid as they leave the orbit.

The small Lacrimal nerve passes along the upper edge of the lateral rectus with the artery of the same name. It passes to the Lacrimal gland, sends branches to it, and then pierces the orbital septum above the lateral palpebral ligament for cutaneous innervation of the upper eyelid. While traveling within the orbit, the Lacrimal nerve picks up a nerve bundle sent over to it from the Zygomatic nerve. This bundle carries postganglionic parasympathetic axons to the Lacrimal nerve for its supply. scan0034.jpg

The Nasociliary nerve passes through the middle compartment of the superior orbital fissure (thus it lies inferolateral to the Optic nerve).

It then passes upward on the lateral side of the Optic nerve, runs anteromedially across its top surface, and then forward along the upper border of Medial rectus.

It gives off branches corresponding to branches of the Ophthalmic artery with the exception that the Frontal nerve will send branches to accompany the Supraorbital and Supratrochlear arteries and the Lacrimal nerve accompanies the Lacrimal branch of the ophthalmic artery. scan0040.jpg

Immediately after it enters the orbit, the Nasociliary nerve is connected to the Ciliary ganglion by a small twig. It has been suggested that some sensory fibers from the eyeball travel with the Short Ciliary nerves to the ganglion and then pass through it into this twig to reach the Nasociliary nerve, which carries them back to VI

Early in its course, the Nasociliary nerve also gives off two Long ciliary nerves that run with the Long Posterior Ciliary arteries parallel to the Optic nerve and pierce the sclera adjacent to it. These carry sensation from the eyeball and, particularly, the cornea. They may also carry postganglionic sympathetic axons to the Dilator Pupillae and vasculature of the eye. After giving off the Long Ciliary nerves, the Nasociliary sometimes gives off a Posterior Ethmoidal nerve but always gives off an Anterior Ethmoidal nerve. These accompany the arteries of the same name and carry sensation from the areas to which the arteries send blood. The terminal branch of the Anterior Ethmoidal nerve accompanies the cutaneous branch of the Anterior Ethmoidal artery onto the surface of the nose.

The cutaneous branch of the artery has no separate name, but the accompanying nerve is called the External Nasal nerve.

Once the Anterior Ethmoidal nerve is given off by the Nasociliary, the latter has no function other than to innervate the skin on the bridge of the nose supplied by the dorsal nasal branch of the Ophthalmic artery.

This part of the Nasociliary nerve is called the Infratrochlear nerve.

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