Anatomy of the trigeminal nerve (CN V)

Chapters:

Watch video only

Introduction0:00–0:55

When it comes to the trigeminal nerve, or CN V, tri means three, so right off the bat, you can tell that the trigeminal nerve has three major branches: the ophthalmic nerve, or V1, the maxillary nerve, or V2, and the mandibular nerve, or V3.
The ophthalmic and the maxillary nerves only have sensory functions, while the mandibular nerve has both sensory and motor functions.
So, the trigeminal nerve is in charge of sensation for the face, mouth, nasal cavity and dura mater of the cranial cavity, and also of motor functions like biting and chewing.
In addition to motor and sensory fibers, postganglionic parasympathetic fibers join many of the branches of the trigeminal nerve to reach their final destination; so the branches of the trigeminal nerve serve as a pathway for parasympathetic innervation.
Now, the trigeminal nerve emerges from the lateral aspect of the pons by a large sensory root and a small motor root. The large sensory root mainly consists of cell bodies of the pseudounipolar neurons that make up the sensory trigeminal ganglion, which sits within a dural recess lateral to the cavernous sinus, called the trigeminal cave.

CN V0:55–4:08

When the ophthalmic, maxillary, and sensory component of the mandibular nerves detect a signal from their sensory nerve endings, the pseudounipolar neurons that make up these nerves transmit their signal through the trigeminal ganglion as first order neurons in the pathway, to synapse in the different trigeminal nuclei located along the brainstem.
The cell bodies of these pseudounipolar nerves are located in the trigeminal ganglion, similar to how the dorsal root ganglions hold the cell bodies for the sensory pseudounipolar neurons of the body.
After synapsing in the trigeminal nuclei, the second order neurons cross the medial plane at the level of the pons and ascend as the trigeminal lemniscus to synapse again in the contralateral thalamus to third order neurons.
These third order neurons then travel through the internal capsule and go on to synapse in the cerebral cortex of the postcentral gyrus where the sensory information is received and interpreted by our brain.
Now, regarding the motor component of the trigeminal nerve: first order neurons from areas such as the cerebral cortex of the precentral gyrus travel through the internal capsule and typically cross the median plane at the level of the pons to synapse in the trigeminal motor nuclei with second order neurons located in the pons of the brainstem.
These second order neurons then exit and pass inferior to the trigeminal ganglion to form the motor component of the mandibular nerve.
The motor fibers blend with the sensory fibers of the mandibular nerve as the nerve traverses the foramen ovale in the cranium.
Eventually, these motor branches innervate the muscles that help with mastication. The trigeminal nerve has four nuclei: one motor called the trigeminal motor nucleus, and three sensory: the mesencephalic nucleus, the principal sensory nucleus or the pontine nucleus, and the spinal trigeminal nucleus.
Each sensory nucleus receives a different type of information. So, the mesencephalic nucleus is located in the lower midbrain and receives proprioception for masticatory muscles, and it also senses deep pressure which prevents you from biting down hard enough to lose a tooth!
The principal sensory nucleus which is located in the pons, receives tactile information from the face and mouth. Finally, the spinal trigeminal nucleus extends down the medulla and into the spinal cord, and receives pain and temperature information from the face.
All these nuclei also receive somatic sensory information from other cranial nerves that carry somatic sensory information such as CN VII, IX and X.

Quiz4:08–4:22

Let’s take a quick break and try to identify the trigeminal nerve and its three major branches. Now, let’s take a look at the first branch of the trigeminal nerve which is the ophthalmic nerve, or cranial nerve V1.

Ophthalmic nerve (V1)4:22–8:28

It originates from the trigeminal ganglion in the middle cranial fossa and passes anteriorly through the lateral wall of the cavernous sinus.
Then, it divides into three branches, all of which pass through the superior orbital fissure to enter the orbit: the frontal nerve which then provides sensory innervation to the forehead and scalp, the lacrimal nerve which supplies the lacrimal gland, and the nasociliary nerve which supplies the eye and nose.
Overall, the ophthalmic nerve transmits sensory fibers from the eyeball, the skin of the upper face and anterior scalp, the lining of the upper part of the nasal cavity and air cells, and the meninges of the anterior cranial fossa.
And now for the specifics.The frontal nerve passes along the roof of the orbit and divides in two branches: the supraorbital nerve and the supratrochlear nerve.
The supraorbital nerve passes through the supraorbital notch along with a branch from the ophthalmic artery and supplies the skin of the forehead and the scalp.
The nasociliary nerve passes through the superior orbital fissure within the common tendinous ring and gives off four branches: the long ciliary nerve, the short ciliary nerve and the anterior and posterior ethmoidal nerves.
The long and short ciliary nerves supply the eyeball, while the short ciliary nerves also carry postganglionic parasympathetic fibers from the Edinger-Westphal nucleus of the oculomotor nerve to the ciliary body and sphincter pupillae.
The preganglionic parasympathetic fibers travel with the oculomotor nerve and synapse in the ciliary ganglion. The ethmoidal nerves give sensory fibers to the meninges of the anterior cranial fossa, and then supply the upper part of the nasal cavity and to the external tip of the nose, as well as the sphenoid and the ethmoidal air cells.
The lacrimal nerve supplies the lacrimal gland and a small area of the adjacent skin and conjunctiva. The lacrimal nerve also carries postganglionic parasympathetic fibers from the pterygopalatine ganglion to innervate the lacrimal gland, which synapse with the preganglionic fibers originating from the superior salivatory nucleus and travel with the facial nerve.
Now, the nasociliary branch of the trigeminal nerve, along with the temporal and zygomatic branches of the facial nerve, collaborate for two reflexes: the corneal reflex and the lacrimal reflex.
In these reflexes, cranial nerve five or the trigeminal nerve is the sensory or afferent pathway, while cranial nerve seven or the facial nerve serves as the motor or efferent pathway.
The corneal reflex, also known as the blink reflex, refers to involuntary blinking that happens when the cornea is stimulated by a foreign body or a bright light - like when a grain of sand gets in your eye, or when someone is pointing a flashlight at your eyes.
The stimulus is sensed by the nasociliary nerve, travels to the ophthalmic nerve and then to the principal sensory nucleus of the trigeminal nerve located in the brainstem.
This nucleus sends signals to the facial motor nucleus to begin the efferent portion of the reflex, and synapses with the facial nerve on each side.
Then, the facial nerve activates the orbicularis oculi muscle which contracts and causes the eyelid to close. So this reflex protects the eyes from foreign bodies and bright lights.
The lacrimal reflex has the same afferent pathway as the blink reflex, and the efferent pathway starts with the preganglionic parasympathetic fibers that travel through the facial nerve to synapse in the pterygopalatine ganglion.
The fibers then travel through various branches to reach the lacrimal nerve which innervates the lacrimal gland, initiating tear production.Let’s take another break and see if you can recognize the ophthalmic nerve and all its branches.

Quiz8:28–8:42

Maxillary nerve (V2)8:42–12:10

Moving on to the second branch of the trigeminal nerve which is the maxillary nerve, or cranial nerve V2, which transmits sensory fibers from the skin of the face between the palpebral fissure and the mouth, from the nasal cavity and the sinuses, and from the maxillary teeth.
From the trigeminal ganglion, cranial nerve V2 passes in the lower part of the lateral wall of the cavernous sinus, goes through the foramen rotundum to the pterygopalatine fossa and divides in two major branches: the infraorbital nerve and the zygomatic nerve, but it also gives smaller branches like the nasal, greater and lesser palatine, and pharyngeal nerves, which supply the nose and the palate.
The infraorbital nerve branches from the trigeminal nerve to enter the pterygopalatine fossa. Then, it passes through the inferior orbital fissure, and runs anteriorly within the infraorbital groove of the orbital floor where it gives off three superior alveolar nerves, which are sensory branches for the maxillary sinus and teeth.
Then it enters the infraorbital canal within the floor of the orbit, and exits through the infraorbital foramen giving off branches that supply the skin of the medial cheek, the lateral nose and the upper lip.
The zygomatic nerve, on the other hand, arises in the pterygopalatine fossa and enters the orbit through the inferior orbital fissure.
Then, it runs in the lateral wall of the orbit where it divides in two small cutaneous branches: the zygomaticotemporal nerve and the zygomaticofacial nerve, which supply the skin over the zygomatic and temporal bones, or more simply the cheek and temple.
The zygomatic nerve carries postganglionic parasympathetic nervous system (PNS) information to the lacrimal nerve as part of the lacrimal reflex, while its preganglionic fibers travel with the nervus intermedius and then the greater petrosal nerve before they synapse in the pterygopalatine ganglion.
The nasal branches pass medially from the pterygopalatine fossa through the sphenopalatine foramen into the nasal cavity where they supply the nasal cavity and the sinuses.
They also carry postganglionic parasympathetic fibers from the pterygopalatine ganglion to the nasal glands. The superior alveolar nerves pass directly through the maxilla to supply the maxillary teeth, gums and sinus.
The greater and lesser palatine nerves provide innervation for the hard and soft palate and also carry postganglionic parasympathetic fibers from the superior salivatory nucleus and pterygopalatine ganglion to the minor salivary glands located in the palatal mucosa.
The pharyngeal branch passes posteriorly to contribute to the sensory supply of the nasopharynx. Now don't forget, along with sensory information there is also special sensory information of the head.
Special sensory information, such as taste, passes from the taste buds on the palate through the palatine nerves, which pass through the pterygopalatine ganglion without synapsing, then go through the pterygoid canal, and finally hitchhike with the greater petrosal nerve back to the facial nerve.
The facial nerve ultimately takes this information back to the brainstem to be processed. That was enough for now.

Quiz12:10–12:28

Take a break and try to identify the maxillary nerve and all its branches.And now let’s look at the third branch of the trigeminal nerve, which is the mandibular nerve, or cranial nerve V3.

Mandibular nerve (V3)12:28–16:39

The mandibular nerve has both sensory and motor functions. Specifically, it has sensory fibers for the skin over the mandible, the side of the cheek and temple, the oral cavity, the external ear, the tympanic membrane and the temporomandibular joint.
Its motor fibers go to the eight muscles derived from the first pharyngeal arch. Remember that the pharyngeal arches are 6 embryological structures, of which only 5 eventually develop into the muscles, arteries, bones and cartilage of the head and neck.
Interestingly enough, each pharyngeal arch is typically associated with a cranial nerve innervating it - so for the first pharyngeal arch, that nerve is the trigeminal nerve!
Now, the 8 muscles are the temporalis, the masseter, the medial and lateral pterygoids, the mylohyoid, the anterior belly of the digastric, the tensor tympani and the tensor veli palatini muscle.
To remember these, think of the four groups of two! Two tensors, two pterygoids, two big muscles - the temporalis and the masseter - and two muscles in the floor of the mouth - the mylohyoid and the anterior belly of the digastric!
Alright, now. From the trigeminal ganglion, the mandibular nerve passes through the foramen ovale and then through the infratemporal fossa where it gives off four branches: the inferior alveolar nerve, the lingual nerve, the auriculotemporal nerve and the buccal nerve.
Now, the inferior alveolar nerve gives off a branch called the nerve to mylohyoid which supplies both the mylohyoid muscle and the anterior belly of the digastric.
Then it passes through the mandibular foramen to enter the mandibular canal where it gives off sensory branches for the lower teeth.
Anteriorly, the nerve gives off the mental nerve which exits the mandible through the mental foramen to supply sensation to the chin and the lower lip.
The lingual nerve travels along the floor of the mouth and provides sensory innervation to the anterior two thirds of the tongue and floor of the mouth.
The lingual nerve also carries preganglionic PNS information from the superior salivatory nucleus, which initially travels with a branch of the facial nerve called the chorda tympani, and finally to the lingual nerve where the fibers synapse in the submandibular ganglion.
Then the postganglionic parasympathetic fibers innervate the submandibular and sublingual glands. Speaking of which, chorda tympani also conveys taste information from the tongue back to the solitary nucleus in the brainstem.
Taste information from the taste buds of the anterior two thirds of the tongue and oral cavity travels through the lingual nerve and then through the chorda tympani, which joins the lingual nerve in the infratemporal fossa, back up to the facial nerve and eventually to the nucleus of the solitary tract in the brainstem.
The next branch of the mandibular nerve is the auriculotemporal nerve, which arises distal to the foramen ovale and encircles the middle meningeal artery.
It supplies the temporomandibular joint, the parotid fascia, the skin of the temple, and most of the skin of the external auditory meatus and tympanic membrane.
It also carries preganglionic parasympathetic information that starts from the inferior salivatory nucleus, then travels with the glossopharyngeal nerve, which is cranial nerve IX.
The PNS fibers synapse in the otic ganglion located in the infratemporal fossa, while postganglionic fibers travel with the auriculotemporal nerve to innervate the parotid gland.
The buccal nerve branch passes between the two heads of the lateral pterygoid muscle, and underneath the temporalis and masseter muscle to give sensory fibers for the skin and mucosa of the cheek.

Quiz16:39–16:57

Time for another break! Try to identify the mandibular nerve and all its branches.
Finally, the mandibular nerve has somatic motor function and gives off branches for the four muscles of mastication, better known as the muscles that help us chew food, which are the temporalis muscle, the masseter muscle, the lateral pterygoid muscle and the medial pterygoid muscle.

Muscles of mastication16:57–17:44

These upper motor neurons begin in the cerebral cortex, where they go and synapse in the trigeminal motor nucleus in the pons of the brainstem to the lower motor neurons.
From here, these fibers bypass the trigeminal ganglion and merge with the sensory component of the mandibular division. Then, after exiting from the foramen ovale, the mandibular nerve sends off motor branches to the four muscles of mastication.
Finally, let’s look at the jaw jerk reflex, where the afferent and efferent pathways are both carried out by the mandibular nerve.

Jaw jerk reflex17:44–18:25

This reflex is used to assess the function of the trigeminal nerve, and also to determine the level of a potential CNS lesion.
The afferent pathway is sensed via the muscle spindles from the masseter muscle, and the sensory information then travels to the mesencephalic nucleus of the trigeminal nerve.
Then, this primary neuron synapses in the trigeminal motor nucleus, where a signal is sent through the motor fibers of the mandibular nerve via the masseteric nerve to contract the masseter muscle, closing the jaw.Alright, as a quick recap.

Review18:25–20:58

The trigeminal nerve is the fifth cranial nerve and provides both sensory and motor functions, while also serving as a highway for parasympathetic innervation.
It has three major branches: the ophthalmic nerve, or V1, the maxillary nerve, or V2, and the mandibular nerve, or V3. The trigeminal nerve has four nuclei: one motor called the trigeminal motor nucleus, and three sensory: the mesencephalic nucleus, the principal sensory nucleus or the pontine nucleus, and the spinal trigeminal nucleus.
The ophthalmic nerve has three branches: the frontal nerve, the nasociliary nerve and the lacrimal nerve. The frontal nerve divides into the supraorbital and supratrochlear branch.
The nasociliary nerve gives off four branches: the long and short ciliary nerves and the anterior and posterior ethmoidal nerves.
The nasociliary nerve along with the temporal and zygomatic branches of the facial nerve work together for two reflexes: the corneal reflex and the lacrimal reflex, and it’s also important in carrying parasympathetic innervation to the ciliary body and sphincter pupillae, as well as the lacrimal gland.
The maxillary nerve divides in two major branches: the infraorbital nerve and the zygomatic nerve, and also gives other branches such as the nasal, superior alveolar, greater and lesser palatine, and pharyngeal nerves, which service as a parasympathetic pathway for the lacrimal, nasal, and palatal salivary glands.
The mandibular nerve is a mixed nerve providing both sensory and motor functions. It gives off four branches: the inferior alveolar nerve, the lingual nerve, the auriculotemporal nerve and the buccal nerve, and provides motor function to the 4 muscles of mastication which are the temporalis muscle, the masseter muscle, the medial and lateral pterygoid muscles.
It helps serve as a pathway for the special sense of taste, and also carries parasympathetic innervation to the parotid,