CRANIAL NERVE V (THE TRIGEMINAL NERVE)

The fifth cranial nerve derives its name – Trigeminal – from the fact that it has three major divisions:

  1. Ophthalmic (V1)
  2. Maxillary (V2)
  3. Mandibular (V3).

Components:

Collectively, the three divisions of the nerve form a great somatic sensory (GSA) pathway to the anterior region of the head, including the:

  1. Face
  2. Temporal region
  3. Scalp
  4. Oral and nasal cavities
  5. Orbit
  6. Paranasal air sinuses
  7. Dura mater

The nerve also possesses a much smaller, branchiomeric motor (SVE) root that joins the mandibular division. These fibers are distributed to the:

  1. Muscles of mastication,
  2. Tensor tympani
  3. Tensor veli palatini (T. palati)
  4. Mylohyoid
  5. Anterior belly of the digastric

        all of which arise from the first branchial (pharyngeal) arch.

Course:

The sensory and motor roots of the trigeminal nerve leave the brain stem through the substance of the pons. Together, they cross the posterior cranial fossa and climb the ridge of the petrous temporal bone toward the middle cranial fossa. Here, they encounter the dura mater as it turns back off the ridge onto the undersurface of the tentorium cerebelli. The nerve doesn’t pierce the dura, nor does the dura blend immediately with the epineurium. Instead, the dura is prolonged around the nerve, over the petrous ridge and into the middle cranial fossa, more specifically into the cavernous dural venous sinus.

This glove-like extension of the dura, from posterior cranial fossa into the cavernous sinus, is called the Trigeminal (Meckle’s) Cave. It is fused with the lateral wall of the sinus and contains the sensory trigeminal ganglion.

The somatic sensory (GSA) Trigeminal (Semilunar) Ganglion is lodged in the Trigeminal Fossa a small depression on the anterior surface of the petrous temporal bone lateral to the cranial entrance of the carotid canal. The ganglion is semilunar in shape.

The sensory root of the trigeminal nerve passes posteromedially from the ganglion back over the petrous ridge into the posterior cranial fossa.

The three divisions of the trigeminal nerve issue forth from the anterolateral convexity of the ganglion.

Communications:

The trigeminal ganglion receives filaments from the postganglionic sympathetic plexus on the internal carotid artery.

Branches:

A number of small meningeal branches leave the ganglion and pass back to the dura of the tentorium cerebelli.

THE OPHTHALMIC NERVE (V1)

Components:

The ophthalmic division of the trigeminal nerve consists of somatic sensory (GSA) fibers destined for the dura mater of the middle and anterior cranial fossae, the forehead, the bridge, sides and tip of the nose, anterior portion of the nasal cavity, upper eyelid, upper half of the orbit, the globe of the eye, and the cornea.

In addition, all branches of the nerve distribute postganglionic sympathetic (GVE) fibers acquired from the internal carotid plexus in the cavernous sinus (see below).

Course:

The Ophthalmic Nerve (V1) leaves the anterior upper margin of the trigeminal ganglion, pierces the anterior wall of the trigeminal cave, and runs forward in the lateral wall of the cavernous sinus toward the superior orbital fissure. As it does so, it lies below the trochlear nerve. Just before it enters the orbit, the nerve divides into its three terminal branches: frontal, lacrimal, and nasociliary nerves.

Communications:

As it traverses the wall of the cavernous sinus, the ophthalmic nerve communicates with the oculomotor, trochlear, and abducent nerves and with the postganglionic sympathetic plexus on the internal carotid artery.

Somatic afferent (GSA) fibers returning from muscle spindles and other sensory endings in the extraocular muscles leave the orbit in the oculomotor, trochlear, and abducent nerves. Most if not all are transferred to the ophthalmic nerve in the cavernous sinus and reach the brainstem with the trigeminal.

Postganglionic sympathetic (GVE) fibers from the internal carotid plexus are widely distributed through the branches of the ophthalmic nerve. Most are destined for blood vessels, including those in the choroid tunic of the eye. Some are carried to the involuntary dilator pupillae muscle by the long ciliary branches of the nasociliary nerve (see below).

Branches:

The tentorial nerve (or meningeal branch) arises from the ophthalmic nerve as it leaves the trigeminal ganglion. This small nerve passes back along the undersurface of the tentorium cerebelli.

The frontal nerve is the largest of the terminal branches arising from the ophthalmic nerve in the superior orbital fissure. It enters the orbit superolateral to the annular tendon and runs forward above levator palpebrae superioris, just beneath the orbital periosteum (periorbita). At a variable distance between the apex and the anterior margin of the orbit, the nerve divides into its supraorbital and supratrochlear branches.

The supraorbital nerve continues anteriorly and leaves the orbit through the supraorbital notch or foramen. Its branches are distributed to the:

  1. upper eyelid and its conjunctiva,

  2. skin of the forehead and scalp as far back as the vertex or, often, the lambdoidal suture,

  3. periosteum of the skull, and

  4. mucous membrane of the frontal air sinus, through a small passage in the roof of the supraorbital foramen.

The supratrochlear nerve is much smaller. It is directed anteromedially and leaves the orbit by passing above the cartilaginous trochlea for the tendon of the superior oblique muscle. Its branches are distributed to the:

  1. upper eyelid and conjunctiva

  2. skin of the lower forehead close to the midline.

The lacrimal nerve is the smallest of the terminal branches of the ophthalmic nerve. It enters the orbit through the lateral extremity of the superior orbital fissure, outside the annular tendon. As it passes forward along the upper border of the lateral rectus muscle, the nerve receives a communicating filament that ascends the orbital wall from the zygomaticotemporal branch of the maxillary nerve. This communication contains parasympathetic secretomotor fibers from the pterygopalatine ganglion destined for the lacrimal gland.

The lacrimal nerve continues forward, passing below the lacrimal gland, to which it sends a series of fine branches. The nerve leaves the orbit by piercing the orbital septum and ends in branches distributed to the lateral aspect of the upper eyelid and conjunctiva.

The nasociliary nerve is the third and last terminal branch of the ophthalmic nerve. It enters the orbit within the annular tendon, between the superior and inferior divisions of the oculomotor nerve. It turns medially across the orbit between the superior rectus muscle and the optic nerve, runs forward along the frontoethmoidal suture between the roof and medial wall of the orbit, and ends by dividing into anterior ethmoidal and infratrochlear nerves.

The sensory root of the ciliary ganglion arises from the nasociliary nerve lateral to the optic nerve, between the ophthalmic artery and the lateral rectus muscle. The term “sensory root” is misleading in that the nerve consists of GSA fibers that pass forward through the ganglion and into the short ciliary nerves without interruption. Ultimately these fibers reach the back of the eye lateral to the entrance of the optic nerve. They supply the eye itself but contribute little, if anything, to sensory innervation of the cornea.

Two or three slender long ciliary nerves leave the nasociliary nerve as it crosses above the optic nerve. They run forward and enter the back of the eye, carrying:

  1. the somatic sensory innervation for the cornea, and

  2. most if not all the postganglionic sympathetic fibers that innervate the involuntary dilator pupillae muscle.

The posterior ethmoidal nerve arises as the nasociliary nerve approaches the medial wall of the orbit. It passes into the posterior ethmoidal foramen, which opens into the frontoethmoidal suture below the roof of the orbit. The nerve thus reaches the posterior ethmoidal air cells and the sphenoidal air sinus immediately behind them.

The anterior ethmoidal nerve is the larger terminal branch of the nasociliary nerve. It leaves the orbit through the anterior ethmoidal foramen, situated on the frontoethmoidal suture. The foramen is the orbital entrance to the anterior ethmoidal canal formed between the orbital plate of the frontal bone and the lateral mass of the ethmoid. The canal conveys the nerve medially, between adjacent ethmoidal air cells, into the anterior cranial fossa, where it opens above the lateral border of the cribriform plate through the cranial aspect of the frontoethmoidal suture. The nerve runs forward between the dura and the bone, in a shallow groove along the suture. It descends into the anterior part of the nasal cavity through a narrow slit at the anterolateral extremity of the cribriform plate. On the roof of the nasal cavity the nerve divides into medial and lateral internal nasal nerves.

The medial internal nasal nerve supplies the anterior upper portion of the nasal septum and its mucous membrane.

The larger lateral internal nasal nerve supplies the upper anterior portion of the lateral nasal wall and continues as the external nasal nerve.

The external nasal nerve emerges between the nasal bone and the nasal cartilage and descends to supply the skin of the side and tip of the nose, as well as the nasal vestibule.

The infratrochlear nerve continues the trajectory of the nasociliary nerve. It runs forward in the superior medial angle of the orbit. It communicates with the supratrochlear branch of the frontal nerve and passes onto the face below the cartilaginous trochlea. It supplies the:

  1. lacrimal sac

  2. conjunctiva

  3. eyelids

  4. skin on the side of the nose above the medial angle of the eye.

THE MAXILLARY NERVE (V2)

Components:

The maxillary division of the trigeminal nerve consists of somatic sensory (GSA) fibers destined for the dura mater of the middle cranial fossa, the side of the nose, upper lip, lower eyelid and conjunctiva, cheek and lateral temporal region, nasal cavity, palate, and upper teeth.

Certain branches distribute postganglionic parasympathetic secretomotor fibers acquired from cells of the pterygopalatine ganglion. These reach the lacrimal gland and glands in the mucous membrane of the nasal cavity, palate, and maxillary sinus.

In addition, all branches of the nerve distribute postganglionic sympathetic (GVE) fibers acquired from the internal carotid plexus either in the cavernous sinus or via the deep petrosal nerve and nerve of the pterygoid canal (see below).

Course:

The Maxillary Nerve (V2) leaves the anterior margin of the trigeminal ganglion, pierces the anterior wall of the trigeminal cave, and runs obliquely forward and downward in the lateral wall of the cavernous sinus toward foramen rotundum. As it does so, it lies below the ophthalmic nerve. The nerve passes through foramen rotundum into the pterygopalatine fossa, where it breaks up into its terminal branches according to a somewhat variable pattern. Here the parasympathetic motor pterygopalatine ganglion is suspended from the nerve by two short stout “roots”.

Beyond the ganglion, the maxillary nerve continues into the inferior orbital fissure as the infraorbital nerve. The infraorbital nerve appears briefly high in the infratemporal fossa, turns forward across the floor of the orbit, and emerges onto the face through the infraorbital foramen.

Communications:

As it traverses the wall of the cavernous sinus, the maxillary nerve communicates with the postganglionic sympathetic (GVE) plexus on the internal carotid artery.

In the pterygopalatine fossa, the nerve receives additional fibers from the internal carotid plexus. These reach the fossa through the deep petrosal nerve and the nerve of the pterygoid canal. They join the maxillary nerve at the level of the pterygopalatine ganglion, through which they pass without synapsing.

At its major branch point in the pterygopalatine fossa, the maxillary nerve acquires postganglionic parasympathetic (GVE) axons from the pterygopalatine ganglion.

The pterygopalatine ganglion is innervated by preganglionic fibers that reach it from the facial nerve via the greater petrosal nerve and nerve of the pterygoid canal.

The maxillary nerve also acquires a small number of taste (SA) fibers from the facial nerve. These accompany the preganglionic parasympathetic fibers in the greater petrosal nerve and nerve of the pterygoid canal but pass through the pterygopalatine ganglion without synapsing.

Postganglionic sympathetic (GVE) fibers from the internal carotid plexus are widely distributed through the branches of the maxillary nerve. These fibers are destined for blood vessels, including those in the lacrimal gland and in the mucous membranes of the nasal cavity, oral cavity, and maxillary sinus.

Postganglionic parasympathetic (GVE) secretomotor fibers from the pterygopalatine ganglion are carried to the lacrimal gland and to glands of the nasal cavity, palate, and maxillary sinus.

Taste (SA) fibers from the facial nerve reach taste buds in the palatal mucous membrane.

Branches.

The maxillary nerve enters the pterygopalatine fossa from the middle cranial fossa by passing through the foramen rotundum. As it gives rise to its terminal branches, the nerve acquires postganglionic parasympathetic fibers from the pterygopalatine ganglion. It also receives taste fibers from the facial nerve and postganglionic sympathetic fibers from the internal carotid plexus both of which reach the fossa from behind through the pterygoid (Vidian) canal.

The nerve is joined in the fossa by the third part of the maxillary artery, which enters from the infratemporal fossa through the pterygomaxillary fissure. Branches of the maxillary nerve pair up with branches of the maxillary artery and their corresponding veins to form typical neurovascular bundles. These bundles then pass out of the pterygopalatine fossa through gaps in its walls to reach their destinations. Therefore, as one learns the branches of the maxillary nerve, one also learns the branches of the last part of the maxillary artery.

The infraorbital nerve is the main continuation of the maxillary nerve beyond the pterygopalatine ganglion. Beyond the ganglion nerve passes into the inferior orbital fissure, traveling toward the inferior lateral angle of the orbit. It appears briefly high in the infratemporal fossa, then turns forward out of the fissure onto the floor of the orbit, where it occupies the infraorbital groove. The nerve descends gradually into the floor of the orbit, passes through the infraorbital canal, and emerges onto the face through the infraorbital foramen.  Here it gives rise to palpebral, nasal and labial branches.

The infraorbital nerve also provides branches to the upper teeth and the lining of the maxillary sinus.  These are given off in the floor of the orbit.

The posterior superior alveolar nerve (or nerves, there may be two or three) arises from the maxillary nerve in the pterygopalatine fossa. It passes through the pterygomaxillary fissure out into the infratemporal fossa and onto the tuberosity of the maxilla. After sending branches to the upper gum and mucous membrane of the cheek, the nerve enters the maxilla through the posterior superior alveolar foramen (foramina).

The nerve runs forward within the maxilla, sending fine branches through the bone to reach the lining of the maxillary sinus. It innervates the upper molar and premolar teeth directly and through the superior dental plexus formed with branches of the anterior and middle superior alveolar nerves.

The zygomatic nerve arises from the maxillary nerve in the pterygopalatine fossa. It runs the length of the inferior orbital fissure beneath the periosteum and passes onto the lateral wall of the orbit, where it divides into its terminal zygomaticofacial and zygomaticotemporal branches. Both branches pass out of the orbit and into the zygomatic bone through the zygomaticoorbital foramen or foramina. Within the bone they diverge from one another.

"Branches of the pterygopalatine ganglion”

The remaining branches of the maxillary nerve are usually described as “branches of the pterygopalatine ganglion.” In fact they all consist of bundles of somatic sensory (GSA) trigeminal fibers that acquire additional types of fibers as they pass through the ganglion.

Fine orbital branches of the pterygopalatine ganglion enter the orbit from the inferior orbital fissure and ramify, forming a delicate retroorbital plexus. The plexus distributes: -sensory trigeminal fibers to the orbital periosteum and lining of the posterior ethmoidal and sphenoidal sinuses.

  1. postganglionic sympathetic fibers to blood vessels of the orbital floor and walls and to the involuntary inferior tarsal muscle.

  2. postganglionic parasympathetic fibers to the lining of the posterior ethmoidal and sphenoidal sinuses and, possibly, to the lacrimal gland.

Posterior superior nasal nerves enter the nasal cavity from the pterygopalatine fossa through the sphenopalatine foramen.

They distribute somatic sensory (GSA) trigeminal fibers, postganglionic parasympathetic secretomotor fibers, and postganglionic sympathetic vasomotor fibers to the mucous membrane of the lateral and medial nasal walls, the posterior ethmoidal air cells, and the anterior inferior surface of the hard palate.

The posterior superior lateral nasal nerves turn forward from the sphenopalatine foramen to reach the mucous membrane covering posterior portions of the upper two nasal conchae and the superior and middle meati.  They also send fine branches to the posterior ethmoidal air cells.

The posterior superior medial nasal nerves proceed medially from the sphenopalatine foramen.  They hug the roof of the nasal cavity and turn downward onto the nasal septum.  One of these, the nasopalatine nerve, is far longer than the rest.

The nasopalatine nerve descends in a groove on the vomer, downward and forward to reach the upper surface of the hard palate.  It passes into the incisive canal and emerges through the incisive fossa onto the roof of the oral cavity behind the central incisor teeth.  Its terminal branches ramify beneath the mucous membrane of the anterior hard palate and intermingle with branches of the greater palatine nerve (see below).

The greater and lesser palatine nerves descend from the pterygopalatine ganglion into the greater palatine canal.  They supply the mucous membrane with somatic sensory (GSA) fibers, postganglionic parasympathetic secretomotor fibers, and postganglionic sympathetic fibers destined for mucosal blood vessels. The lesser palatine nerves also distribute SA fibers to taste buds in the mucous membrane of the soft palate.

 The greater palatine nerve runs vertically downward in the canal and emerges onto the undersurface of the hard palate through the greater palatine foramen.  It turns forward beneath the mucous membrane and intermingles with terminal branches of the nasopalatine nerve.

 The posterior inferior nasal nerves leave the greater palatine nerve, pierce the anterior wall of the greater palatine canal, and pass forward supplying the mucous membrane over the inferior nasal concha and the inferior meatus.

 The lesser palatine nerves (there are usually at least two) angle posteriorly as they descend and leave the greater palatine canal in one or more lesser palatine canals.  These open onto the undersurface of the hard palate through the lesser palatine foramina, from which the nerves supply the soft palate. They also join with fibers from the tonsillar branches of the glossopharyngeal nerve to form a tonsillar plexus.

 The small pharyngeal nerve passes back from the pterygopalatine ganglion through the palatovaginal canal to reach the pharyngeal recess behind the torus tubarius (pharyngeal entrance of the auditory tube).  It supplies somatic sensory (GSA) fibers, postganglionic parasympathetic secretomotor fibers, and postganglionic sympathetic vasomotor fibers to a small area of nasopharyngeal mucous membrane in the recess and around the opening of the auditory tube.    

THE MANDIBULAR NERVE (V3)

PENDING