Download The Ophthalmic Nerve HO

The Fifth Cranial Nerves
“The Trigeminal”
By
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.
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.
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.
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.
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.
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.
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.