Although nuclei are not required knowledge, they are interesting
The trigeminal nerve arises from four separate nuclei the extend from the midbrain into the spinal cord. The motor nucleus is the smallest and lies lateral to the principal sensory nucleus in the upper pons, near the ventral surface of the 4th ventricle. The three sensory nucleus include the mesencephalic, principal sensory and spinal nucleus of the trigeminal nerve. These lie in sequence from the midbrain (mesencephalic nucleus), upper pons (principle sensory) and medulla/spinal cord (spinal nucleus).
- The motor nucleus is the origin of motor supply for the muscles innervated by the trigeminal nerve (muscles of mastication)
- The mesencephalic nucleus is involved in unconscious proprioception
- The principal sensory nucleus is responsible for fine touch and conscious proprioception
- The spinal nucleus is responsible for pain and temperature sensation
The spinal nucleus also receives pain and temperature fibres from the glossopharyngeal (IX) and vagus (X) nerves
Within the brainstem, motor fibres travel separately to the sensory fibres. The sensory fibres to the mesencephalic nucleus and spinal nucleus from the mesencephalic tract and spinal tract of the trigeminal nerve.
Course of Trigeminal Nerve
The trigeminal nerve arise anteriorly from the upper lateral pons as two roots (motor and sensory). The motor root is much smaller. The sensory root passes beneath the tentorium cereberi, anteriorly to the trigeminal ganglion. The motor root does not enter the ganglion, instead passing inferiorly to exit the cranium through the foramen ovale with the mandibular division of the ganglion.
The trigeminal ganglion a large ganglion which lies posterior and lateral to the cavernous sinus within a dural recess known as the trigeminal cave (or Meckel's cave). The cell bodies of sensory neurons lie within the ganglion. Three nerves arise from the ganglion - the ophthalmic, maxillary and mandibular nerves which are numbered from rostral to caudal (V1, V2, and V3).
Ophthalmic Nerve (V1)
The sensory-only ophthalmic nerve is the smallest of the trigeminal branches. It passes anteriorly along the lateral wall of the cavernous sinus, covered by the venous endothelium and below the oculomotor and trochlear nerves. Just before leaving the cranium through superior orbital fissure, it divides into the nasociliary, frontal and lacrimal nerves.
The frontal nerve is the largest and most superior of the branches of V1. It passes along the roof of the orbit, superior to levator palpebrae superiorus. It divides into the supratrochlear nerve and the supraorbital nerve at the midpoint of the orbital roof.
This nerve passes medially along the roof and medial wall of the orbit, passing over the trochlea and exiting from the anteromedial aspect of the orbit. It supplies the skin of the upper eyelid and the most medial part of the forehead.
The supraorbital nerve continues the course of the frontal nerve, and exits the orbit through the supraorbital foramen or notch. It passes superiorly to supply the skin of the forehead and central upper eyelid/conjunctiva.
The lacrimal nerve is the smallest branch of V1. It passes through the lateral orbit, superior to the lateral rectus muscle. It receives a small branch from the zygomatic nerve (via V2) which carries parasympathetic fibres from the pterygopalatine ganglion (via VII). The nerve pierces the lacrimal gland, which receives the parasympathetic fibres but no contribution from the V1 fibres. The lacrimal nerve supplies the skin of the lateral outer eyelid and nearby face.
This nerve passes along the medial side of the orbit, below the superior rectus/oblique and accompanying the ophthalmic artery. It gives off anterior and posterior ethmoidal branches, as well as contributing to the ciliary ganglion and terminating as the infratrochlear nerve.
Sensory root of the ciliary ganglion
The sensory root of the ciliary ganglion arises from the nasociliary nerve and conveys general sensory fibres from the the eyeball (particularly the cornea). The nerve fibres merely pass through the ciliary ganglion and do not synapse.
Posterior ethmoidal nerve
The posterior ethmoidal nerve enters the paranasal sinuses through the posterior ethmoid canal, and carries general sensory information from the posterior ethmoid air cells, the frontal sinus and sphenoid sinus.
Anterior ethmoidal nerve
The anterior ethmoidal passes into the anterior ethmodial canal, giving supply to the anterior ethmoidal air cells and the frontal sinus. It then ascends into the anterior cranial fossa. Within the fossa, it passes anteriorly beneath the dura and above the cribriform plate, before entering a slit adjacent to the crista galli (the spikey bit in the midline that arises from the cribriform plate). It then descends internal surface of the nasal bone and provides general sensory supply to the superior and anterior parts of the lateral wall of the nasal cavity and the nasal septum. The nerve gives off an external nasal branch, which passes into the subcutaneous tissue of the nose to supply the skin of the nose.
The infratrochlear nerve continues along the medial wall of the orbit, passing beneath the trochlea and exiting the orbit to supply the skin of the eyelid, lacrimal canaliculi and the upper lateral nose.
Maxillary Nerve (V2)
The maxillary nerve is the second division of the trigeminal and is also a pure sensory nerve. It passes anteriorly, through the inferior part of the lateral wall of the cavernous sinus (inferior to V1) and exits the cranium through foramen rotundum. Before it exits it gives off a small meningeal branch which supplies the dura mater. The nerve exits this foramen into the deep part of the pterygopalatine fossa. Within the pterygopalatine fossa it gives off two large branches to the pterygopalatine ganglion, as well as the posterior superior alveolar and zygomatic nerves. The nerve then passes through the inferior orbital fissure into the orbit. It travels along the floor of the orbit in the infraorbital groove which becomes the infraorbital canal. When it enters the canal the nerve is renamed the infraorbital nerve.
The point at which the maxillary nerve becomes the infraorbital nerve is debatable. The description from Gray's Anatomy is what I have used. Moore's Anatomy says the nerve changes name as soon as it leaves the pterygopalatine fossa through the inferior orbital fissure. If I get asked "please describe the trigeminal nerve and its named branches" I think I'll mention this!
The small meningeal branch of the maxillary nerve accompanies the middle meningeal vessels arising through foramen spinosum.
The nerve is connected by two branches to the pterygopalatine ganglion, forming its sensory roots. This ganglion is deeply seated within the pterygopalatine fossa and receives its autonomic supply from the nerve of the pterygoid canal (mixture of sympathetic supply from the internal carotid plexus and parasympathetics from the greater petrosal nerve (VII)). There are numerous branches which arise from the ganglion, carrying a mixture of general sensory and autonomic supply. Importantly, nerves from the trigeminal ganglion do not synapse in the ganglion.
Greater palatine nerve
The greater palatine nerve passes inferiorly within the pterygopalatine fossa and enters the greater palatine canal. It emerges on the roof of the oral cavity from the greater palatine foramen and passes anteriorly and medially towards the incisors (these are supplied by the nasopalatine nerve, below). It supplies the anterior soft palate, the hard palate and also gives off branches to the lateral nasal cavity.
Lesser palatine nerves
The lesser palatine nerves are smaller branches that also exit the pterygopalatine fossa through the greater palatine canal. Within the canal they take a different course and exit into the oral cavity through the lesser palatine foramen. These nerves supply the mucosa of the soft palate (including the uvula) and the tonsillar fossa.
Posterior superior nasal nerves
These small nerves pass medially through the sphenopalatine foramen. They supply the lateral walls and posterior roof of the nasal cavity, and the posterior part of the nasal septum.
This much larger nerve also passes through the sphenopalatine foramen to enter the nasal cavity. It passes across the superior posterior part of the cavity and then descends along the septum. It passes anteriorly along the floor of the nasal cavity adjacent to the septum before descending into the incisive foramen to supply the anterior hard palate.
The pharyngeal branch passes through the palatovaginal canal on the posterior wall of the pterygopalatine foramen to enter the nasopharynx. It supplies a small part of the nasopharynx behind the pharyngotympanic tube.
The zygomatic nerve arises in the pterygopalatine fossa and also passes into the orbit through the inferior orbital fissure. It divides into three branches.
This small nerve passes through a canal in the zygomatic bone to emerge in the infratemporal fossa. It pierces the temporalis muscle and supplies the skin over the temple.
This other division of the zygomatic nerve leaves the orbit through a small canal in the zygomatic bone, near the infero-lateral part of the orbital rim. It supplies the skin over the cheekbone.
Communicating branch with the lacrimal nerve
The zygomatic nerve also gives off a small branch that joins with the lacrimal nerve (a branch of V1). This nerve carries parasympathetic fibres from the pterygopalatine ganglion to the lacrimal gland.
Superior alveolar nerves
The superior alveolar nerves are the posterior, middle and anterior. They supply the teeth and gingiva of the maxillary alveolar process.
Posterior Superior Alveolar Nerve
The PSAN branches from the maxillary nerve in the pterygopalatine fossa. It enters the maxilla and passes along the posterior wall of the maxillary sinus,which it supplies. It then joins the superior alveolar plexus which runs beneath the roots of the maxillary teeth, supplying them and the surrounding gingiva.
Middle Superior Alveolar Nerve
The MSAN leaves the infraorbital nerve within the infraorbital canal, and passes along the medial wall of the maxillary sinus to supply the premolar teeth.
Anterior Superior Alveolar Nerve
The ASAN passes along the anterior wall of the maxillary sinus to supply the incisors and adjoining gingiva.
The terminal branch of the maxillary nerve, the infraorbital nerve passes anteriorly beneath the orbit in the infraorbital canal. This canal opens onto the face and divides into nasal, palpebral and superior labial branches. These supply the skin of the lower eyelid, the ala of the nose and the superior lip.
Mandibular Nerve (V3)
The mandibular nerve is the largest division of the trigeminal and has both sensory and motor functions. The sensory root passes inferiorly from the trigeminal ganglion to exit the cranium from foramen ovale. The motor root of the trigeminal, which does not enter the ganglion, passes beneath and exits through foramen ovale, uniting with the sensory root outside the skull. It descends between tensor veli palatini and the lateral pterygoid, giving off a meningeal and a nerve to medial pterygoid before dividing into an anterior and posterior trunk.
The meningeal branch passes laterally and re-enters the cranium through foramen spinosum with the middle meningeal. It supplies the dura of the middle cranial fossa.
The anterior trunk is mostly motor in nature, giving branches to the pterygoids, masseter and temporalis. Buccinator is supplied by the facial nerve. The buccal branch of the anterior trunk passes anteriorly to merge with buccal branches of the facial nerve. This nerve supplies the skin and mucosa of the cheek as well as the buccal gingiva.
The posterior trunk is much larger and mostly sensory. It divides into three large branches and is in close proximity to the otic ganglion.
This nerve passes posteriorly and laterally behind the temporomandibular joint, deep to the superior parotid. It then passes superiorly, anterior to the external auditory meatus, to supply the skin of the lateral scalp.
The lingual nerve passes inferiorly to the junction of the ramus and body of the mandible. It then passes anteriorly along the internal surface of the mandible. Upon reaching the mylohyoid, it passes medially on its internal surface to the root of the tongue. From here it divides to supply the lingual mucosa. Taste fibres from the anterior 2/3rds of the tongue accompany the lingual nerve to its origin, where they depart as the chorda tympani. The submandibular ganglion also lies near the lingual nerve, to which it supplies a parasympathetic root. Pre-ganglionic fibres arrive in the ganglion from the chorda tympani.
Inferior alveolar nerve
The other terminal branch of the posterior division, the inferior alveolar follows a similar initial course to the lingual but enters the mandible on its internal surface at the mandibular foramen. Before entering the mandible it gives off a mylohyoid branch which passes on the external surface of mylohyoid and supplies that muscle. The inferior alveolar nerve then lies within the mandibular canal, which it follows beneath the alveolar process to supply the teeth. The inferior alveolar nerve divides within the mandible to give rise to the mental nerve (which supplies the chin) and the incisive nerve (which supplies the incisors and adjacent mucosa).