Hello, everyone. This is Joao from Kenhub, and welcome to another anatomy tutorial where, this time, we’re going to be talking about the nerves of the orbit.
So what we’re going to be doing here on this tutorial is exploring the different nerves that you find on the orbit.
And right now, we’re looking the superior view of the cranium where we just made a cut so we can expose here, as you can see, the orbit and the different nerves here represented in yellow.
These are the structures that we’re going to be talking about in a little bit more detail throughout this tutorial.
We’re going to be seeing here on this tutorial that we are finding five of the 12 cranial nerves on this area that we’re going to be talking about. And that includes the cranial nerve number two, the optic.
We’re also going to see the oculomotor or the third cranial nerve, the trochlear which is the fourth cranial nerve, the trigeminal or the fifth cranial nerve, and the abducens or the sixth cranial nerve.
Let’s have a look at the first one here on this list that I’m highlighting in green. Notice here that, now, we’re looking at a lateral view, a cut here of the orbit.
So we can expose the different contents of the orbit including some of the blood vessels, some muscles here; but in yellow, you see the different nerves. And we’re highlighting this structure here that is known as the optic nerve.
As I mentioned before, the optic nerve is the second cranial nerve and leaves the orbit via the optic canal running posteromedially towards the optic chiasm. This nerve transmits visual information from the retina to the brain.
Your eyes’ blind spot is a result of the absence of photoreceptors in the area of the retina where the optic nerve leaves the eye, so a bit of a fun fact here on this tutorial.
And now we’re looking at another image that we saw in the beginning. So this is the superior view of the orbit where you can clearly see now the optic nerve highlighted in green and how it exits the … or leaves the orbit via the optic canal running posteromedially towards then the optic chiasm.
Next on our list, we’re going to also see another cranial nerve seen here highlighted in green. This is the oculomotor nerve. And as you probably remember, this one is the third cranial nerve. And it enters the orbit via the superior orbital fissure and controls most of the eyes’ movements.
The oculomotor nerve will give off two branches. One is the superior branch and another one is an inferior branch which you can also see here. So this is the superior branch and the inferior branch.
The oculomotor nerve also will be supplying parasympathetic fibers to the eye. And for that reason, controlling the sphincter pupillae muscle and affecting that way the pupil constriction and the ciliary muscle which then affects accommodation.
We’re going to move on to the next structure that you see here highlighted in green, one that we already talked about. Yes, this is the superior branch of the oculomotor nerve.
Now, the superior branch of the oculomotor nerve is smaller and it passes medially over the optic nerve, and the superior branch will be superior rectus and the levator palpebrae superioris muscles.
We’re going to move on to, now, what you see here. This is then seen on the lateral view of the orbit, the inferior branch of the oculomotor nerve.
This one is the larger of the two, and it divides into three branches. One branch will be passing beneath the optic nerve and will be supplying then the medial rectus muscle.
Another branch will be then innervating the inferior rectus muscle, and the third longus runs forward to the inferior oblique muscle.
We’re moving on to another cranial nerve that you see here highlighted in green from a superior view. We’re looking at the trochlear nerve.
This one is the fourth cranial nerve, and it is a motor nerve that innervates a single muscle which is then the superior oblique muscle of the eye.
And here on this image, you can also see here this muscle which is the superior oblique muscle of the eye.
The trochlear nerve is unique among the cranial nerves in several aspects. It is the smallest nerve in terms of number of axons it contains. It has the greatest intracranial length. And it is the only cranial nerve that exits from the caudal aspect of the brain stem.
We’re moving on to another cranial nerve that you see here highlighted in green. This is known as the trigeminal nerve.
The trigeminal nerve is the fifth cranial nerve. It is a nerve responsible for sensation in the face and certain motor functions such as biting and chewing.
It is the largest of the cranial nerves, and it gives off three branches which you can also see here from this image clearly.
One of them is going to be the ophthalmic branch; this one right here. Another one will be the maxillary; this branch right here. And the third one will be the mandibular; this branch right about here on this image.
You can also see the trigeminal nerve from a superior view and the three branches – the ophthalmic, the maxillary, and mandibular.
We’re going to start off by talking about the ophthalmic nerve which is then a branch of the trigeminal nerve that I talked about. So this is a branch of the fifth cranial nerve.
The ophthalmic nerve carries only sensory fibers. The ophthalmic nerve will be then supplying branches to or specifically three branches to various structures of the orbit and face. These include the nasociliary nerve, the lacrimal nerve, and the frontal nerve.
Now, let’s take a look at this one that you see here highlighted in green. This is the nasociliary nerve, which as I mentioned before, this is a branch of the ophthalmic nerve; and it innervates the mucous membrane of the nasal cavity.
The nasociliary nerve will be giving off several branches which include the posterior ethmoidal nerve, the long ciliary nerves, the infratrochlear nerve, the sensory root of the ciliary ganglion, and the anterior ethmoidal nerve. And a good way to remember these is using this mnemonic – PLICA. So write this down on your notes.
Now, we’re going to move on and talk about a branch that we’ve just listed, the posterior ethmoidal nerve which you see here highlighted in green just branching off of this one that we talked about the nasociliary nerve.
So as you can see, this is a branch of the nasociliary nerve.
The posterior ethmoidal nerve passes through the posterior ethmoidal foramen with the posterior ethmoidal artery. It carries sensory information from the sphenoid sinus and posterior ethmoidal air cells, and it is absent at about thirty percent of people.
Next, we’re going to be talking about these highlighted in green which are the long ciliary nerves. There are two or three in number, and they are branches of the nasociliary nerve. And the long ciliary nerves provide sensory innervation into the eyeball including the cornea.
Next in line are going to be … or this nerve that you see here highlighted in green. This one is the infratrochlear nerve.
The infratrochlear nerve is also a branch of the nasociliary nerve just before it enters the anterior ethmoidal foramen. So the anterior ethmoidal foramen should be right about here.
Notice how the branch then starts this infratrochlear nerve starts right about where the nasociliary nerve will be entering the anterior ethmoidal foramen.
This nerve will be supplying the skin of the upper eyelids and branch of the nose, the conjunctiva, the lacrimal sac, and the caruncle.
Now, before we talk about the sensory root of the ciliary ganglion, we should first clarify what the ciliary ganglion really is.
You see it here highlighted in green; this is the ciliary ganglion. And this is a parasympathetic ganglion located in the posterior orbit.
Now, there are three types of nerve fibers that run through the ciliary ganglion. There are the parasympathetic fibers, sympathetic fibers, and sensory fibers.
Only parasympathetic fibers form synapses in the ganglion. The other two types of nerve fibers will simply pass through here.
And now we’re ready to move on to then what you see here highlighted in green. And this really thin, thin, thin highlight. This is known as the sensory root of the ciliary ganglion.
It is made of sensory fibers from the cornea, iris, and ciliary body that run posteriorly through the short ciliary nerves and pass through the ciliary ganglion without forming synapses.
Now, we’re going to talk about these really short, thin filaments that are known as the short ciliary nerves. Now, the short ciliary nerves are branches of the ciliary ganglion.
There are about six to ten in numbers which arise from then the anterior part of the ganglion in two bundles as you can see here. And they pierce the sclera as you can see here at the posterior part of the ball of the eye and pass through in delicate grooves on the inner surface of the sclera and then will be supplying the ciliary muscle, the iris, and the cornea.
Next we’re going to be talking about this small highlight that you see here on the nasociliary nerve, a branch of the nasociliary nerve. And this is the anterior ethmoidal nerve.
Now, anterior ethmoidal nerve is the continuation of the nasociliary nerve. After that, it enters the anterior ethmoidal foramen into the anterior ethmoidal air cells.
The anterior ethmoidal nerve arises only after the nasociliary has given off its other branches.
This nerve will be sending sensory fibers to the middle and anterior ethmoidal air cells, also to the meninges and the anterior part of the nasal septum, and the skin on the lateral sides of the nose.
The next nerve that we’re going to be seen here highlighted in green piercing this gland, this is known as the lacrimal nerve.
Now, the lacrimal nerve is the smallest of the three branches of the ophthalmic nerve. It travels forward in a separate tube of dura mater and enters the orbit through the narrowest part of the superior orbital fissure.
This nerve will be providing sensory innervation for then the lacrimal gland, the conjunctiva, and the lateral upper eyelids.
The next nerve that we’re going to be talking about is seen here highlighted in green, a very thin structure that you see on this image. The name of this branch, this is known as the communicating branch of the lacrimal nerve with the zygomatic nerve.
It is a nerve branch by which the postsynaptic parasympathetic fibers from the pterygoid palatine ganglion are transferred from the zygomatic nerve, which you see here, all the way to then this nerve that we talked about which is the lacrimal nerve for distribution to then the lacrimal gland.
Next nerve that we’re going to be seeing here on the lateral view of the orbit; this highlighted in green is known as the frontal nerve.
The frontal nerve is the largest branch of the ophthalmic nerve and maybe regarded both from its size and direction as the continuation of the nerve.
This nerve enters the orbit through the superior orbital fissure. Midway between the apex and base of the orbit, it divides into two branches, the super trochlear and the supraorbital nerve which we will be talking about next.
The frontal nerve will be then providing sensory innervation for the skin of the forehead, the mucosa of the frontal sinus, and the skin of the upper eyelid.
Now, let’s talk about one of these branches come out of the frontal nerve. This highlighted in green is known as the supratrochlear nerve which as I mentioned is a branch of the frontal nerve and it passes above the pulley of the superior oblique muscle which you can see here on this image. So this is the superior oblique muscle and you notice how this passes superior to it.
The supratrochlear nerve exits the orbit between the pulley of the superior oblique and the supraorbital foramen.
This nerve will be then supplying the skin of the lower part of the forehead and close to the midline, the conjunctiva and the skin of the upper eyelid.
Next branch of the frontal nerve that we’re going to be seeing here highlighted in green. This one is the supraorbital nerve.
Now, the supraorbital nerve is a terminal branch of the frontal nerve and it will be innervating a few structures including the upper eyelids, the conjunctiva of the eye, the frontal sinus, the skin from the forehead extending back to the midline of the scalp, and the integument of the scalp, and not to forget also the pericranium.
Now, the next nerve that we’re going to talk about that you see here highlighted in green, this is the maxillary nerve which is a second branch of the trigeminal nerve.
It goes through the foramen rotundum and then travels through its branches across the infraorbital groove and canal in the floor of the orbit. And it appears upon the face at the infraorbital foramen. And there, it is called the infraorbital nerve, a terminal branch.
The maxillary nerve transmits sensory fibers from the maxillary teeth, the skin between the palpebral fissure, and the mouth, and from the nasal cavity and sinuses.
Next one that we’re going to be seeing here highlighted in green, this is known as the infraorbital nerve which is a branch of the maxillary nerve and the … or infraorbital canal.
This nerve innervates the lower eyelid, the upper lip, and part or the nasal vestibule, and exits the infraorbital foramen of the maxilla which you can also see here on this image.
Next nerve that we’re going to be seeing here highlighted in green, this one is known as the zygomatic nerve which is also a branch of the maxillary nerve.
It enters the orbit by the inferior orbital fissure and divides at the back of that cavity into two branches, the zygomatical temporal nerve and the zygomatical facial nerve. And you can also see here where the nerve is going to be splitting.
Now, the zygomatic nerve will be innervating the skin over the zygomatic and temporal bones and also the lacrimal gland.
Last nerve that we’re going to be talking about, also a cranial nerve, this is the abducens nerve. Now, this is cranial nerve number six.
It enters the orbit through the superior orbital fissure. It is a somatic efferent nerve that controls the movement of the lateral rectus muscle of the eye.