Test your understanding with 10 random multiple-choice questions from the question bank.
Introduction
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What’s up, Taim Talks Med here. Let’s continue our Cranial nerve series. Cranial
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nerves are twelve pairs of nerves that exit the brain and the brainstem, and in this segment,
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we’ll talk detailed about the fifth cranial nerve, which is the Trigeminal nerve.
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And we’ll do that by first making a quick scheme of the trochlear pathway to get an
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overview of it. Then we’ll cover the nerve in a little more
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detail, by first talking about the distribution of the trigeminal nerve nuclei within the
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brainstem. Then we’ll talk detailed about each branch of the trigeminal nerve, which
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is the ophthalmic nerve, maxillary nerve, and the mandibular nerve. You’ll often see
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them labelled as V1, V2 and V3. The V refers to the Roman numeral “5,” as the trigeminal
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nerve is the fifth cranial nerve, so these numbers refer to the divisions of this nerve
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according to the region of the face they innervate. When we’re done, we’ll quickly go through
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a fun clinical correlation that I think the general population should be aware of when
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it comes to this nerve. Alright. Awesome, let’s start by making
Trigeminal Nerve Scheme
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a rough and simplified scheme. Now, this nerve is primarily responsible for the sensory innervation
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of the face, and motor control of the muscles involved in mastication, or chewing. Right?
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It starts with three sensory nuclei, called mesencephalic, principal and the spinal nuclei
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of the trigeminal nerve, and one motor nucleus, all located within the brainstem. The sensory
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nuclei all have a sensory root that goes towards them, coming from a ganglion called the trigeminal
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ganglion. Now, the way the sensory distribution of the trigeminal nerve is formed is by three
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divisions. We got the ophthalmic, for the forehead and eyes, maxillary for the region
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of the middle face. And the mandibular, for the lower Face and jaw. The motor nucleus
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will give off motor fibers which will join the mandibular division, to innervate primarily
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the muscles of mastication. Now I’ll go through this scheme pretty fast,
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and then we’ll talk about it in a little more detailed, and then I’ll show this scheme
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again at the end of this video as a recap so you hopefully will understand a bit more
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about this nerve. And don’t get overwhelmed by the amount, we’ll try to break it down
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as simple as we can. So. Opthalmic nerve. The ophthalmic nerve will go through the superior
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orbital fissure, but before it does that, it’ll give a tentorial nerve, providing
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sensory innervation to the dura mater of the middle cranial fossa. Once the ophthalmic
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nerve goes through the superior orbital fissure, it receives three fibers. And the three main
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nerves that come together to form V1 are the nasociliary, frontal, and lacrimal nerves.
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The acronym NFL (as in American football) is also useful to recall these three branches.
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The frontal nerve goes directly beneath the roof of the orbit, and extends into two terminal
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division, called supraorbital nerve and the supratrochlear nerve. The supraorbital nerve
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goes up towards the forehead, where it splits into two of its own terminal branches; lateral
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branch and medial branch. The nasocilliary will go through the common
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tendinous ring, and splits into the posterior ethmoidal nerves going through the posterior
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ethmoid foramen and the orbito-ethmoidal canal where it innervates the mucosa of the ethmoid
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cells and sphenoid sinus. There’s the anterior ethmoid nerves which enters through the anterior
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ethmoid foramen and the foramina of the cribriform plate to innervates roof of the nasal cavity.
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We got long and short ciliary nerves for the eyes. And the infratrochlear nerve for the
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upper eyelid and the conjunctiva. And we got the lacrimal nerve, which is the
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thinnest branch of the ophthalmic nerve, going to the lacrimal gland and the upper eyelid.
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The maxillary nerve will go through the foramen rotundum. Before enters the foramen, it gives
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off a meningeal branch that detects stimuli from the dura of the middle cranial fossa.
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Once it enters the pterygopalatine fossa, it gives off 2-3 nerves to the pterygopalatine
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ganglion. Then what happens is that it gives off three branches. The posterior superior
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alveolar nerve, Infraorbital nerve and the zygomatic nerve. The zygomatic and the infraorbital
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nerves will enter the orbital cavity through the inferior orbital fissure. Now the zygomatic
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nerve as it runs through here it gives off two branches, the zygomaticotemporal branch
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and the zygomaticofacial branch, which both run through their own respective foramina.
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The infraorbital nerve will run on the floor of the orbital cavity. On it’s way, it’s
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going to give off the middle superior alveolar nerve and the anterior superior alveolar nerve.
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Then the nerve goes through the infraorbital groove, or foramen, and give off three branches.
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It gives off the inferior palpebral nerve, we got the nasal branches and the superior
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labial branches for the upper lips. The third branch here is the posterior superior
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alveolar nerve. So that’s the big part of the maxillary
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nerve. But there’s other branches that we need to talk about in respect to the pterygopalatine
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ganglion. One branch is going to the pharyngeal area, called pharyngeal nerve. There’s the
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nasopalatine nerve, and we got the lesser palatine for the soft palate and the greater
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palatine for the hard palate. Now there’re some other couple fo branches here too but
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I’m only focusing on some important ones to not make this too overwhelming.
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One important connection here before we go further is a connection between the zygomatic
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and the lactimal nerve. It’s a communicating branch that provide parasympathetic innervation
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for the lacrimal gland. Alright. Let’s do V3, the mandibular. Notice
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how motor fibers from the motor nuclei passes below the trigeminal ganglion without synapsing
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with it, and joins the sensory root of the nerve. This nerve will leave the neurocranium
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through the foramen ovale. And just as it leaves, it gives off the meningeal branch,
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which goes back into the neurocranium through the foramen spinosum. Now keep in might there
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might be some variations here but we’ll keep it at that.
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The V3 division is then going to give off the auriculotemporal nerve. The auroculotemporal
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nerve is composed of two roots that makes a small loop, encirceling the middle meningeal
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artery, to supply the ear and the temporal region. There’s a ganglion here called the
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Otic ganglion. There’s gonna be post-ganglionic parasympathetic secretomotor nerve fibres
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from the otic ganglion, that join and “hitch-hike” along the auriculotemporal nerve to innervate
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the parotid gland. Then we got the lingual nerve, which is sensory
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for the anterior ⅔ of the tongue. Then we got the inferior alveolar nerve. It’s
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going to split into the nerve of the mylohyoid muscle, which innervation to the mylohyoid
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and anterior belly of the digastric muscle respectively, which are responsible for elevating
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the hyoid and the complex movements of the jaw (speaking, swallowing, chewing, and breathing).
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The inferior alveolar nerve resumes its course to enter the mandibular foramen, and reach
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the mandibular canal. Within the mandibular canal, it give off branches to supply the
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teeth of the mandible. Henche the name inferior alveolar. The nerve then continues as the
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mental nerve, which is considered as the terminal branch of the inferior alveolar nerve. The
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mental nerve then passes the mental foramen of mandible to emerge on the face and innervate
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the lower lip. It give off the buccal nerve, which innervates
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the skin of the cheek and buccal mucosa. And then we got all these muscular branches responsible
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for different functions, primarily mastication. Alright, so again this is just a scheme. A
Trigeminal Nerve Nucleus
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superficial way that hopefully will make sense once we talk quickly through each nerve.
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Awesome, so let’s go quickly through the course in a little more detail. So here we
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see the spinal cord, medulla, cerebellum, Pons, mesencephalon, and the diencephalon.
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If we remove the cerebellum and focus only on the posterior side of the brainstem, we’ll
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see this. We can see the medulla, pons and the mesencephalon. Now, I’ll only show the
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left side, but keep in mind that everything you see on the left side you’ll also find
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on the right side. Remember, there’re are three sensory nuclei and one motor nucleus
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for the trigeminal nerve. The first sensory is the mesencephalic nucleus, which receives
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proprioception information from the masticatory muscles. Involved in processing information
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about the position of the jaw/teeth. It is functionally responsible for preventing excessive
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biting that may damage the teeth. Then we got the principal nucleus of the trigeminal
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nerve, which primarily is the main sensory nucleus that receives facial sensation of
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touch. We got the spinal nucleus of the trigeminal nerve, which receives information about things
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like pain, and temperature from the ipsilateral face. And then lastly we got the motor nucleus,
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providing motor innervation for the muscles of mastication, the tensor tympani, tensor
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veli palatini, mylohyoid, and anterior belly of the digastric.
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So, those are the nuclei of the trigeminal nerve. Now. The sensory root of the trigeminal
Course of the Trigeminal Nerve
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nerve will leave the anterior-lateral surface of pons, as you see here.
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Now, if we look from this angle, you’ll see the sensory root of the trigeminal nerve,
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and right next to it, underneath it, you’ll see the motor root of the trigeminal nerve.
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And as you see here. The sensory root comes from the trigeminal ganglion, while the motor
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root skips the trigeminal ganglion completely. So this is what it looks like from a lateral
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view. We got the sensory and the motor root. And the sensory root forms the trigeminal
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ganglion. Now. On the other side of the trigeminal nerve, we got some divisions. These are sensory
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divisions coming from the facial area. And these are the Ophthalmic nerve, Maxillary
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nerve, and the mandibular nerve. Let’s now go through them one by one, starting with
Ophthalmic Nerve (V1)
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the ophthalmic nerve. Now the ophthalmic nerve is the most superior
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branch of the trigeminal nerve, and it’s purely a sensory nerve. And it innervates
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the upper part of the face. And that includes structures associated with the eyes, the nasal
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cavity, the scalp and the dura mater of the anterior cranial fossa. So let’s see how
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it does that. The ophthalmic nerve is going to pass through
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the superior orbital fissure, and enter the orbital cavity. But before it does that, it’ll
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give off a tentorial nerve, providing sensory innervation to the dura mater of the middle
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cranial fossa. Once the ophthalmic nerve goes through the superior orbital fissure, it receives
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three fibers. Frontal nerve, Nasocilliary, and the lacrimal nerve. The frontal nerve
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is the thickest branch of the ophthalmic nerve. It courses forwards, directly beneath the
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roof of the orbit. Inside the orbit, the nerve divides into two terminal branches. The supraorbital
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nerve and the supratrochlear nerve. The supraorbital nerve passes through the supraorbitalnotch,
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goes up to the forehead, and splits into a lateral branch and a medial branch, to supply
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the skin of the lower forehead which they procide with sensory innervation. The supratrochlear
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nerve goes goes upward and medially on the forehead, exiting the skull through the supratrochlear
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foramen, and provides sensory innervation to the skin of the forehead and scalp near
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the midline, just above the nose. Then we got the lacrimal nerve. This nerve
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goes along the roof of the orbit and travels towards the lacrimal gland. So it innervates
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the lacrimal gland, and also some sensory innervation to the upper eyelid aswell.
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Then we got the nasocilliary nerve. This nerve runs from the lateral part of the orbit to
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its medial wall. On its way, it gives off a communicating branch for the ciliary ganglion
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that enters the ciliary ganglion. So it carries sensory fibres for the eyeball, which pass
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through the ciliary ganglion and then continue as the short ciliary nerves to reach the eyeball.
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It also give off long ciliary nerves that penetrate the sclera to innervate the sclera
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and the choroidea. It also give off the posterior ethmoid nerve,
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that leaves the orbit through the posterior ethmoidal foramen and enters the anterior
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cranial fossa. It then descends to the roof of the nasal cavity through the cribriform
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plate, where it innervates the mucosa of the ethmoid cells and sphenoid sinus. The nasocilliary
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nerve also give off the anterior ethmoid nerve, that passes through the anterior ethmoid foramen
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where it reaches the anterior cranial fossa. Then it goes through one of the foramina of
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the cribriform plate to reach the anterior part of the roof of the nasal cavity, where
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it innervates the mucosa of that part. And lastly we got the infratrochlear nerve which
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extends forward to innervation of the skin of the medial portion of the upper eyelid
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and the conjunctiva. Alright so that was mainly all the branches that I wanted to talk about
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regarding the ophthalmic nerve. Now, let’s talk about V2, the maxillary
Maxillary Nerve (V2)
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branch of the trigeminal nerve. The maxillary nerve is purely a somatosensory nerve aswell,
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that carries information from the midface, that is all the structures from the lower
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eyelid to the upper teeth and lips. Now. While the maxillary nerve is in the cranium. It
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gives off meningeal branch that carries the sensory impulses from the dura mater of the
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middle cranial fossa. The nerve then runs through foramen rotundum,
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as you see here. It goes through this foramen, to reach a space called the pterygopalatine
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fossa. Once the maxillary nerve is within the pterygopalatine fossa, it give off branches
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that go to the pterygopalatine ganglion. It’ll also give off Superior Posterior Alveolar
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Branches, and then it’ll give off two terminal branches that goes through the inferior orbital
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fissure, as you see here. These are the infraorbital nerve, and the zygomatic nerve. Alright. Let’s
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go through these nerves, starting with the infraorbital nerve.
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The infraorbital nerve is the strongest branch of the maxillary nerve. After it crosses through
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the inferior orbital fissure, it goes over the inferior wall of the orbit. The infraorbital
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nerve first goes through the infraorbital sulcus and then to the infraorbital canal.
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At the end of the canal, it goes out through the infraorbital foramen. Before it exits
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the infraorbital canal, it gives off the anterior superior alveolar branches and the middle
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superior alveolar branch, which participate in making the plexus that innervate the teeth
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of the upper jaw, together with the posterior superior alveolar branches. We’ll talk about
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it in a minute. But, now the nerve is going to exit the infraorbital canal, through the
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infraorbital foramen. It’s then going to dicide into the Inferior palpebral branches
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that provide innervation for the lower eyelid, external nasal branches that innervate the
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skin that covers the side of the nose, internal nasal branches which provide sensory innervation
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to the nasal septum, and the superior labial branches that innervate the upper lip.
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Alright, that was the infraorbital nerve. The posterior superior alveolar branches,
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as we said leaves the maxillary nerve in the pterygopalatine fossa. They then cross through
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the alveolar foramina on the maxillary tuberosity and enter the alveolar canals. This is where
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they form a plexus that innervate the teeth of the upper jaw, together woth the anterior
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superior alveolar branches and the middle superior alveolar branches.
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Alright, so that was these nerves. Next let’s talk about the zygomatic nerve. Remember it
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comes from the maxillary nerve in the pterygopalatine fossa, and then goes through the inferior
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orbital fissure and enters the orbit. While inside the orbit, the nerve goes along the
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inferior orbital wall, and branches off to give the Zygomaticofacial branch that reaches
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the upper lateral part of the cheek via the zygomaticofacial foramen to innervates the
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skin of the zygomatic region And the Zygomaticotemporal branch, that reaches
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the temporal fossa by passing through the zygomaticotemporal foramen, innervating the
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skin of the temporal region Another important thing to mention about this
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nerve is that on the lateral wall of the orbit, the zygomatic nerve makes anastomosis with
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the lacrimal nerve. And thanks to this anastomosis, parasympathetic fibers from the pterygopalatine
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ganglion reach the lacrimal gland to make it squeeze some tears.
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Alright. Now. The next thing we need to talk about now is the parasympathetic ganglion,
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which received sensory fibers from the maxillary nerve. We’re not gonna go too detailed about
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this one, but it do receive sensory fibers from the facial nerve aswell. The pterygopalatine
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ganglion then give off certain fibers, like the pharyngeal branches that go off to innervate
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the mucous membrane of the nasopharynx. It gives off the nasopalatine that provides sensory
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innervation to the nasal septum, and gingiva. There’s the greater palatine branches for
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primarily the hard palate, and the lesser palatine branches, primarily sensory innervation
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of the soft palate, along with the tonsils and the uvula. There are some other ones aswell
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but I’ll keep it at these ones for the sake of simplicity.
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Alright. So we did the ophthalmic division, we did the maxillary division. Let’s now
Mandibular Nerve (V3)
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do the mandibular divition. The mandibular division contain both sensory
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and motor fibers, right? It provides somatosensory innervation to the skin of the lower part
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of the face, so the lower lip, part of the cheek and chin, teeth of the lower jaw and
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part of the oral mucosa. The motor fibers innervate 8 muscles In total. 4 masticatory
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muscles, anterior belly of digastric, mylohyoid, tensor veli palatini and tensor tympani. Alright
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let’s break this nerve down starting with the somatosensory nerves.
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The nerve travels through the foramen ovale to reach the infratemporal fossa, as you see
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here. Now, just as the nerve leaves the skull, it give off the meningeal branch, which re-enters
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the neurocranium by going back through the foramen spinosum, as you see here. To innervate
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the dura mater of the middle cranial fossa. Then we got the auriculotemporal nerve. The
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way this works is that out from the mandibular nerve, two roots are gonna go out and encircle
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the middle meningeal artery. When these two roots meet, they form the auriculotemporal
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nerve. This nerve innervates part of the auricle and the skin of the temporal region.
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Then we got the lingual nerve, which is a thick nerve giving sensory innervation of
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the anterior 2/3 of the tongue. Then a bit more superiorly here we can see the buccal
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nerve, which innervates the skin of the cheek and buccal mucosa. Then back here we can see
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a small ganglion called the otic ganglion. Now, the otic ganglion. Now I’m not gonna
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spend too much time on this one, but the otic ganglion is one of the parasympathetic ganglions
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we have in the head that provide function to multiple salivary glands. And what this
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one does is that it gives off post-ganglionic parasympathetic secretomotor nerve fibres
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that join and “hitch-hike” along the auriculotemporal nerve to innervate the parotid gland to produce
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saliva. Then we got the inferior alveolar nerve. This
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one is going enter the mandibular foramen, and pass through the mandibular canal. Within
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the mandibular canal, it give off branches to supply the teeth of the mandible. Henche
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the name inferior alveolar. The nerve then continues as the mental nerve, which is considered
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as the terminal branch of the inferior alveolar nerve. The mental nerve then passes the mental
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foramen of mandible to emerge on the face and innervate the lower lip.
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Before entering the mandibular foramen, it gives rise to the nerve of mylohyoid muscle,
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which provide motor innervation to the mylohyoid and anterior belly of the digastric muscle
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respectively. Then we got the deep temporal nerves, we got
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one anterior and one posterior branch. Both of them innervate the temporalis muscle.
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We got the medial pterygoid nerve, innervating the medial pterygoid muscle. The nerve then
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penetrates the medial pterygoid and reaches the tensor tympani and tensor veli palatini,
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which it also innervates. And we got the nerve to lateral pterygoid, which innervates the
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lateral pterygoid muscle. Then we got the masseteric nerve, which innervates
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the temporomandibular joint, as well as the masseter muscle. So that was everything I
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had for the trigeminal nerve. One last thing that I wanna mention about
Clinical Relevance
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this nerve that’s kinda interesting. You’ve probably heard about the virus herpes simplex
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type 1 (HSV-1). Herpes virus is a neurotropic virus that infects the peripheral and central
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nervous systems. After primary infection in epithelial cells, HSV-1 spreads retrogradely
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to the peripheral nervous system, where it establishes a latent infection in the trigeminal
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ganglia. And it usually stays there for the rest of one persons life in the trigeminal
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ganglion. And when the person passes a period with decreased immunity, they’ll get a secondary
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infection of this virus again. Alright. So now we’ve gone through all the
Recap
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most important branches of the trigeminal nerve. Here you have the overview once again.
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It looks harder than it is. The trigeminal nerve is large but quite comprehensible.
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So that was everything I had for the fifth cranial nerve. The next video is going to
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be about the sixth cranial nerve, the abducens nerve.
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Thank you so much for watching another one of my videos. If you enjoyed, learned something
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from it, please remember to like, comment your favourite moment, subscribe. Turn on
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those notifications. If you looking for other ways to support, go ahead and check out the
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link in the description box. Have fun ya’ll. Peace.
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