CN5
Nuclei
Motor nucleus of the trigeminal nerve (V)
- Special visceral efferent fibres
- Arise from the motor nucleus of the nerve located at the level of upper pons
- Innervate the muscles of mastication
- Located in the pons.
Trigeminal sensory nucleus
- Comprises 3 distinct nuclei:
- Mesencephalic nucleus
- Proprioceptive
- Midbrain
- Main sensory nucleus
- Light touch
- Pons
- Spinal trigeminal tract nucleus
- Pain and temperature
- Pons + medulla
- Contains
- Pars Oralis
- Hypoglossal nucleus to motor nucleus
- Pars interpolaris
- Obex to hypoglossal nucleus
- Pars Caudalis
- C2/3 to obex
- An extension of the dorsal root entry zone and substantia gelatinosa of the trigeminal system into the lower medullary and high cervical regions
- Receive input from
- Trigeminal (V)
- Facial (VII)
- Glossopharyngeal (IX)
- Vagus (X)
Exit from the pons
- Lateral pons near CPA
- Root divisions
- There are anastomoses between the fibres from each division in the area posterior to the ganglion
- 1st division
- V1 (Ophthalmic) exits the skull base via SOF
- Rostromedial position
- 2nd division
- V2 (Maxillary) exit skull base via Foramen rotundum
- Intermediate position
- 3rd division
- V3 (Mandibular) exits skull base via Foramen ovale. Contains all motor neurones (which do not enter ganglion) en route to infratemporal fossa
- Caudolateral position
- Leaves the post. fossa via the trigeminal impression to enter the middle fossa and forms the large ganglion (Gasserian ganglion) within the cavernous sinus
- Meckel’s cave
- A dural recess in the posteromedial portion of the middle cranial fossa that acts as a conduit for the trigeminal nerve between the prepontine cistern and the cavernous sinus, and houses the Gasserian ganglion and proximal rootlets of the trigeminal nerve.
- Shaped like an open-ended three-fingered glove pointing anterosuperomedially
- Palm of the glove rests within a bony indentation of the petrous apex (impressio trigemini) and contains the semilunar-shaped Gasserian ganglion of the trigeminal nerve.
- Fingers of the glove, superior to inferior, contain the three postganglionic rootlets that comprise the “tri-” of the trigeminal nerve—ophthalmic (V1), maxillary (V2) and mandibular (V3)
- The cuff of the glove or the entrance of the cave, the porus trigeminus, is between the superior and inferior petrosal sinuses and contains the trigeminal nerve with an arachnoid sheath
- Relations
- Inferior medial: Internal carotid artery precavernous segment
- Anteriorly: cavernous sinus,
- Superomedial: lateral wall of cavernous sinus
- Clinically important
- A major pathway in perineural spread of pathologies such as head and neck neoplasms
- Key structure in assessing trigeminal neuralgia
- Rt trigeminal nerve
- Meckel’s cave, the cistern, which extends forward from the posterior fossa along the posterior trigeminal root to the level of the mid portion of the ganglion, has been exposed by removing the lateral dural wall of the cave.
- The motor root arises rostral to the sensory root and passes through Meckel’s cave on the medial side of the posterior sensory root and ganglion.
- The dura has been removed to expose the posterior root and ganglion and the three trigeminal divisions.
- There are diffuse anastomoses between the rootlets posterior to the ganglion
- Four motor rootlets, which arise around the rostral margin of the sensory root, have been elevated to expose the anastomoses between the motor and sensory roots.
- The cerebellar lip projects forward and may hide the junction of the sensory root with the pons in the retrosigmoid approach
Anatomical images
Nerve course
- Intracranial:
- The trigeminal nerve is attached to the ventrolateral surface of the pons by two roots
- Large lateral sensory root
- Small medial motor root.
- The sensory root contains a ganglion (trigeminal/ Gasserian ganglion)
- Located: at the apex of petrous part of the temporal bone in the Meckel’s cave.
- The trigeminal ganglion divides into three branches:
- Ophthalmic
- Sensory
- Maxillary
- Sensory
- Mandibular
- Motor
- Sensory fibres
- Images
- The nasal cavity, sphenoid sinus, and orbit have been unroofed.
- The dura has been removed from the roof and lateral wall of the cavernous sinus.
- The medial strip below the anterior cranial base is formed, from anterior to posterior, by the frontal, ethmoidal, and sphenoid sinuses.
- The orbital fat has been removed to expose the intraorbital structures.
- The frontal nerve courses above the levator muscle.
- The trochlear nerve passes above the annular tendon to reach the superior oblique muscle.
- The trochlea of the superior oblique muscle is attached in the superomedial part of the anterior orbit.
- The lacrimal nerve courses above the lateral rectus muscle.
- The ophthalmic artery and superior ophthalmic vein are seen in the interval between the levator and superior oblique muscle.
- The anterior and posterior ethmoidal branches of the ophthalmic artery course through the anterior and posterior ethmoidal canals.
- The superior oblique, levator, and superior rectus muscles have been removed.
- The ophthalmic artery and nasociliary nerve enter the orbital apex on the lateral side of the optic nerve and cross between the optic nerve and superior rectus muscle to reach the medial part of the orbit.
- The optic nerve has been elevated to expose the ophthalmic artery, which courses through the optic canal on the lower side of the optic nerve and enters the orbital apex on the lateral side of the optic nerve.
- The ophthalmic artery then crosses medially between the optic nerve and superior rectus muscle, as does the nasociliary nerve.
- The maxillary nerve exits the foramen rotundum to enter the pterygopalatine fossa, and the mandibular nerve exits the foramen ovale to enter the infratemporal fossa.
- Extracranial:
- Ophthalmic nerve exits superior orbital fissure
- Branches and distribution of ophthalmic nerve
- Maxillary nerve exits foramen rotundum
- Branches and distribution of maxillary nerve
- Mandibular nerve exits foramen ovale
- Branches and distribution of mandibular nerve
- The anterior belly of the digastric is innervated by CN V, whereas the posterior belly of the digastric muscle is innervated by CN VII.
Branches | Distribution |
Frontal supratrochlear | Skin of lower forehead |
Frontal supraorbital | Skin of scalp up to vertex, frontal sinus |
Lacrimal | Lateral conjunctiva |
Nasociliary anterior ethmoidal | Anterior ethmoidal air cells, middle ethmoidal air cells, anterosuperior quadrant of lateral wall of nose, anterosuperior part of septum of nose |
Nasociliary posterior ethmoidal | Posterior ethmoidal air cells, sphenoidal air sinus |
Nasociliary Infratrochlear | Conjunctiva over medial aspect, skin of root of nose |
Nasociliary external nasal | Skin of external aspect of nose |
Branches | Distribution |
Posterior superior alveolar | Molar teeth of upper jaw |
Ganglionic Palatine | Palatine mucosa |
Ganglionic Nasal | Nasal mucosa |
Ganglionic Pharyngeal | Mucosa of nasopharynx |
Zygomaticofacial | Skin of the prominence of cheek |
Zygomaticotemporal | Skin of the temporal region of scalp; Postganglionic fibres of lacrimal gland |
Infraorbital Palpebral | Skin and conjunctiva of lower eyelid |
Infraorbital Middle superior alveolar | Premolar teeth of upper jaw |
Infraorbital Anterior superior alveolar | Canine and incisor teeth of upper jaw |
Infraorbital Superior labial | Skin of upper lip including philtrum |
Branches | Distribution |
Nervus spinosus | Dura of middle cranial fossa |
Nerve to medial pterygoid | Medial pterygoid, tensor veli palatini, tensor tympani |
Anterior division Buccal | Skin over buccinator, mucosa of the vestibule of mouth |
Anterior division deep temporal | Temporalis |
Anterior division Masseteric | Masseter |
Anterior division Nerve to lateral pterygoid | Lateral pterygoid |
Posterior division Auriculotemporal | Temporomandibular joint, skin over pinna, external acoustic meatus, tympanic membrane, skin of temporal region of scalp |
Posterior division Lingual | Mucosa of anterior 2/3 of tongue, gums of lower jaw, mucosa of floor of mouth |
Posterior division Inferior alveolar | Mylohyoid muscle and anterior belly of digastric muscle, all teeth of lower jaw, skin of chin and lower lip, mucosa of lower lip |
Review of Blood Supply
Structures | Arteries |
SpTTr & SpTNu in Medulla | Caudal third, Vertebral; Rostral two-thirds, Posterior inferior cerebellar |
SpTTr & SpTNu in Pons | Long circumferential branches of basilar |
Trigeminothalamic fibers in Midbrain | Short circumferential branches of posterior cerebral and superior cerebellar |
VPM | Thalamogeniculate branches of posterior cerebral |
Posterior limb of IC | Lateral striate branches of middle cerebral |
Reflexes Mediated by Trigeminal Nerve
Reflex | Afferent Limb | Efferent Limb |
Corneal reflex | Ophthalmic nerve | Facial nerve |
Conjunctival reflex | Ophthalmic / Maxillary nerve | Facial nerve |
Lacrimation reflex | Ophthalmic nerve | Facial nerve |
Sneezing reflex | Maxillary nerve | Vagus nerve |
Jaw-jerk (Masseteric) reflex | Mandibular nerve | Mandibular nerve |
Function
Sensory supply
- General somatic afferent fibres
- Master sensory nerve of face and head.
- Light touch, Pain and temp
- From
- The skin of the face
- The mucous membrane of the mouth and nose.
- Peripheral processes of unipolar neurons in the trigeminal ganglion.
- Central processes terminate in the main sensory nucleus in upper pons and in the spinal nucleus of the nerve extending up to spinal cord.
- Perioral tingling and numbness in syringobulbia is due to compression of the spinal trigeminal tract.
- Proprioceptive
- From
- Muscles of mastication
- Ocular, facial, and lingual muscles
- Peripheral processes of unipolar neurons located in the mesencephalic nucleus of this nerve located in the midbrain.
- Central processes terminate in the main sensory nucleus.
Motor function
- Motor - Special Visceral Efferent (SVE)
- Innervates 8 muscles
- Voluntary motor innervation to 4 muscles of mastication (contents of infratemporal fossa):
- Temporalis
- Masseter
- Medial and Lateral Pterygoids
- 4 additional muscles:
- Tensor tympani
- Tensor veli palatini
- Mylohyoid
- Anterior belly of digastric
Associated with autonomic nerves
- Parasympathetic ganglia of the head are attached to CN5 and use it as a conduit to their destination
- Several SVEs ride the trigeminal nerve to innervate
- Salivary glands (submandibular, sublingual, parotid)
- The palate
- The nasal glands and
- The glands of the tongue
- It gets these parasympathetic fibers from the VII. and IX. nerves.
- The postganglionic fibers of these nerves join to the sensory branches of the trigeminal nerve
Assessment
- Function and Testing
- Sensory function can be tested in two ways:
- Touch: By touching different areas of the skin with a wisp of cotton wool.
- Pain: By applying gentle pressure with a pin.
- Motor function
- Asking the patient to clench their teeth firmly; the contraction of the masseter muscle can then be felt by palpation.
Clinical
- Effects of Injury or Disease
- Paralysis of Pterygoid Muscles:
- The muscles of mastication control the side-to-side movements of the mandible, and their balanced tone keeps the chin in the midline. When the pterygoid muscles on one side are paralysed, the chin is pushed to the paralysed side by the functioning muscles of the opposite side.
- Ophthalmic Division Injury:
- Loss of sensation in the cornea abolishes the protective corneal reflex, which is the automatic closing of eyelids when the cornea is touched. This can lead to corneal ulcers and potentially blindness.
- Referred Pain
- Referred pain occurs when pain originating in a structure supplied by one branch of the nerve is felt in a skin area supplied by a different branch.
- Examples of Referred Pain:
- Caries in a lower jaw tooth may cause pain to be felt in the ear.
- An ulcer or cancer on the tongue may cause pain to be felt over the ear and temple.
- In frontal sinusitis, pain is referred to the forehead.
- Headache is a common symptom when any structure supplied by the trigeminal nerve, such as the eyes, ears, or teeth, is involved.
- Trigeminal Neuralgia
- This condition is characterised by severe, persistent pain in the skin area supplied by the nerve, often caused by a source of irritation.
- Link with Trigeminal Neuralgia
- Clinical Procedures
- Mandibular Nerve Block: This procedure is used to anaesthetise the lower jaw for procedures like tooth extraction by injecting an anaesthetic near the inferior alveolar nerve before it enters the mandibular canal.
- Lingual Nerve Considerations:
- The lingual nerve is located very close to the medial side of the third molar tooth and is at risk of injury during careless extraction of that tooth.
- For intractable pain from tongue cancer, the nerve can be surgically cut at this site to provide relief.
Images
Abbreviation | Full Form | Abbreviation | Full Form | Abbreviation | Full Form |
ALS | Anterolateral system | MaxV | Maxillary division of trigeminal nerve | TriMoNu | Trigeminal motor nucleus |
CC | Crus cerebri | MesNu | Mesencephalic nucleus | TMJ | Temporomandibular joint |
CSNu | Chief (principal) sensory nucleus | ML | Medial lemniscus | VPL | Ventral posterolateral nucleus of thalamus |
DTTr | Dorsal trigeminothalamic tract | OpthV | Ophthalmic division of trigeminal nerve | VPM | Ventral posteromedial nucleus of thalamus |
FacNu | Facial nucleus | RB | Restiform body | VTTr | Ventral trigeminothalamic tract |
GSA | General somatic afferent | RetF | Reticular formation | Ganglia 1 | Trigeminal ganglion |
HyNu | Hypoglossal nucleus | RNu | Red nucleus | Ganglia 2 | Geniculate ganglion |
IC | Internal capsule | SpTNu | Spinal trigeminal nucleus | Ganglia 3 | Superior glossopharyngeal |
ManV | Mandibular division of trigeminal nerve | SpTTr | Spinal trigeminal tract | Ganglia 4 | ㅤ |
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