CNV Trigeminal Nerve

Authors

Affiliations

Nate Yomogida, B.S., SPT

Doctor of Physical Therapy

B.S. in Kinesiology

Chloë Kerstein, B.S., SPT

Doctor of Physical Therapy

B.A. in Neuroscience

Trigeminal Nerve Sensory and Motor pathways (from Blumenfeld figure 12.7¹)

Nerves of the Orbit

Nerves of the orbit and ciliar ganglion (lateral view)²

Oblique section through the right cavernous sinus²

The path and connections of CN VII Facial nerve in the temporal bone²

Upper part of medulla spinalis, hindbrain, and midbrain (posterior view)²

“Ventral view of Surface Anatomy of the brainstem and cranial nerves (from fig12.2 of Blumenfeld¹)”

“Dorsal view of Surface Anatomy of the brainstem and cranial nerves (from fig12.2 of Blumenfeld¹)”

“Lateral view of the surface Anatomy of the brainstem and cranial nerves (from fig12.2 of Blumenfeld¹)”

“Skull foramina serving as cranial nerve exit points (from fig12.3 of Blumenfeld¹)”

Note

• Welzack Chapter 56 Trigeminal Mechanisms of Nociception³
• Welzack Chapter 58 Migraine and the Trigeminal Autonomic Cephalalgias³
• Welzack Chapter 66 Trigeminal and Glossopharyngeal Neuralgia³

Overview

CN V Trigeminal nerve is the largest cranial nerve and provides general somatic sensory to the scalp, teeth, oral and nasal cavity as well as branchial motor functions to the muscles of mastication and some surrounding musculature^1,4.

Additional functions

• Additionally, The trigeminal system plays a role in facial and dural sensitivity and has also been considered a component in brain nociceptive innervation⁵.
• “Proprioceptive nerve fibers from the masticatory muscles and (probably) extraocular muscle”⁴.

The Trigeminal nerve’s course can be broken down into: - Brainstem - Cisternal segment - Meckel’s cave segment - Trigeminal ganglion - Pperipheral divisions: Opthalmic division (V₁), Maxillary division (V₂), and Mandibular division (V₃).

Why should I care about this nerve? - The trigeminal nerve is the anatomical substrate of several pathologies or conditions, including: Headaches (primary or secondary), trigeminal neuralgia, and alternate types of orofacial pains⁵. - Understanding the complex anatomical arrangement of CN V’s pathway is crucial to understand these conditions’ pathophysiology and treatment⁵.

Trigeminal Nuclei

There are 4 trigeminal nuclei (3 sensory and 1 motor):

• Mesencephalic nucleus (Conveys afferent proprioceptive fibers from extraocular and masticatory muscles and allows for bite modulation⁴)
• Trigeminal sensory nucleus
  • Conveys touch and proprioception of the jaw area -ninjanerd
  • Conveys tactile and pressure sense⁴
• Trigeminal motor nucleus (Modulates degree of bite)
• Spinal trigeminal nucleus Conveys touch, pain, pressure, and proprioception from the entire face
  • Spinal Trigeminal tract

Anatomy

Brainstem

Trigeminal Root (Cisternal Segment)

• The 4 trigeminal nuclei (3 sensory, 1 motor) extend throughout most of the brain stem⁴
• “The trigeminal root is composed of the large sensory root and the small motor root”⁴
• “The sensory root receives somatosensory sensation from the entire face , temple, external acoustic meatus, and the anterior scalp as far posterior as the vertex of the skull”⁴

Note

The trigeminal nerve supplies somatosensation to the entire face except the angle of the jaw innervated by the cervical plexus⁴

The proprioceptive impulses from the masticatory muscle run through the motor root to enter the mesencephalic nucleus⁴

Sensory Root (Portio Major)

Sensory Pathway

Trigeminal Sensory System Nuclei and Pathways (from Blumenfeld figure 12.8¹)

• Somatosensory afferent nerves convey crude touch, pain, and temperature sensation from the face and mouth to the lateral pons¹.
• These nerve fibers then descend the spinal trigeminal tract to synapse in the spinal trigeminal nucleus¹.
• . Similarly, the spinal trigeminal tract is analogous to Lissauer’s tract (see Figures 6.4 and 7.2). Secondary sensory neurons from the spinal trigeminal nucleus cross the brainstem to ascend as the trigeminothalamic tract (or ventral trigeminothalamic tract). The trigeminothalamic tract is analogous to the spinothalamic tract (see Table 12.6), and the pathways travel together to the thalamus (see Figures 12.8 and 14.3). Trigeminothalamic tract fibers synapse in the thalamic ventral posterior medial nucleus (VPM), and tertiary sensory neurons then travel in the internal capsule to the primary somatosensory cortex. Like the anterolateral systems in the spinal cord, there are also pathways from the spinal trigeminal nucleus to intralaminar thalamic nuclei, the reticular formation, and other areas, to mediate the affective and arousal aspects of facial pain.

In summary, it is generally believed that sensory fibers involved in the conduction of pain and temperature spread over the trigeminal sensory nucleus complex (TSNC) and then cross over to the contralateral thalamus and cerebral cortex⁶

Sensory Function

• V₁ Opthalmic supplies the upper face
• V₂ Maxillary supplies the middle face
• V₃ Mandibular supplies the lower face

The trigeminal nerve also provides touch and pain sensation for the nasal sinuses, inside of the nose, mouth, and anterior two-thirds of the tongue.

Dysfunction

• Trigeminal neuralgia

Motor Root (Portio Minor)

Motor Pathway

• The motor plan is sent from the cerebrum/cerebellum inferiorly to the trigeminal motor nucleus
• From there, the motor signal exits the trigeminal motor nucleus and passes anteriorly in the pons⁷
• The motor root emerges from the ant-lat aspect of the pons⁷
  • The motor root is anterior and medial relative to sensory root⁷
• Next, the motor root passes through the posterior fossa and then through the dura mater below the attachment of the tentorium⁷
• The motor root then enters Meckel Cave⁷
  • travels beneath the trigeminal ganglia⁷
  • Exits the skull through foramen ovale⁷
• Upon its exodus from the skull, the motor root joins the sensory fibers in the mandibular (V₃) division to form the mandibular nerve
• The mandibular nerve (V₃) connects the motor root to the masticatory muscles (masseter, temporalis, and medial and lateral pterygoid muscles)⁷
  • In addition, motor fibers are given off to the tensor tympani, tensor veli palatini, and mylohyoid muscles, and to the anterior belly of the digastric muscle”⁷

Motor Function

Meninges Sensitivity

The trigeminal system not only supports sensation to the face, but also the dura and pia⁵.

Brain innervation

Pathways

• The trigeminal nerve exits the brainstem from the ventrolateral pons¹.
• Next CN V enters Meckel’s Cave (a small fossa posterior and inferolateral to the cavernous sinus)¹.
• CN V synapses on the trigeminal ganglion (sensory ganglion) in Meckel’s cave⁸.
• The ophthalmic division (V₁) travels through an inferior section of the cavernous sinus and exits the skull through the superior orbital fissure¹.
• The maxillary division (V₂) exits via the foramen rotundum¹
• The mandibular division (V₃) via the foramen ovale¹

Mnemonic

A way to remember the exit points of each trigeminal division is “Standing Room Occupancy”, or SRO (for Superior, Rotundum, Ovale)

In addition, pain sensation for the supratentorial dura mater is supplied by the trigeminal nerve, while the dura of the posterior fossa is innervated by CN X and upper cervical nerve roots.

Skin of face –> Receptor –> fine touch/dental pressure –> DIVISION –> Chief trigeminal sensory nucleus –> Trigeminal lemniscus –> VPM of thalamus

Skin of face –> Receptor –> Proprioception –> DIVISION –> Mesencephalic trigeminal nucleus –> ?

Skin of face –> Receptor –> Crude touch / Pain / Temperature –> DIVISION –> trigeminothalamic tract –> VPM of Thalamus

Trigeminal Ganglion

(AKA “semilunar ganglion” or “gasserian ganglion”)

Analagous Trigeminal and Spinal Somatosensory Systems

Nucleus	Sensory Modalities	Main pathway to thalamus	Main thalamic nucleus
Mesencephalic trigeminal nucleus	Proprioception	-	-
Chief trigeminal sensory nucleus	fine tough; dental pressure	Trigeminal Lemniscus	VPM
Spinal trigeminal nucleus	Crude touch; Pain; Temperature	Trigeminothalamic tract	VPM
Posterior column nuclei	Fine tough; proprioception	Medial lemniscus	VPL
Dorsal horn	Crude touch; Pain; Temperature	Spinothalamic Tract	VPL

Testing

• Jaw Jerk Reflex

External Resources

• Ninja Nerd’s Trigeminal Nerve video
• Brazis’s localization in neurology contains a solid overview and really good DDX⁷

References

1.

Blumenfeld H. Neuroanatomy Through Clinical Cases. 3rd ed. Oxford university press; 2022.

2.

Gray H. Anatomy of the Human Body. 20th ed. (Lewis WH, ed.). Lea & Febiger; 1918. https://www.bartleby.com/107/

3.

McMahon SB, ed. Wall and Melzack’s Textbook of Pain. 6th ed. Elsevier/Saunders; 2013.

4.

Joo W, Yoshioka F, Funaki T, Mizokami K, Rhoton AL. Microsurgical anatomy of the trigeminal nerve. Clinical Anatomy. 2014;27(1):61-88. doi:10.1002/ca.22330

5.

Terrier LM, Hadjikhani N, Destrieux C. The trigeminal pathways. Journal of Neurology. 2022;269(7):3443-3460. doi:10.1007/s00415-022-11002-4

6.

Henssen DJHA, Kurt E, Kozicz T, van Dongen R, Bartels RHMA, van Cappellen van Walsum AM. New Insights in Trigeminal Anatomy: A Double Orofacial Tract for Nociceptive Input. Frontiers in Neuroanatomy. 2016;10:53. doi:10.3389/fnana.2016.00053

7.

Brazis PW, Masdeu JC, Biller J. Localization in Clinical Neurology. 8th ed. Wolters Kluwer Health; 2022.

8.

Blumenfeld H. Neuroanatomical Basis of Consciousness. In: The Neurology of Conciousness. 2nd ed. Elsevier; 2016:3-29. doi:10.1016/B978-0-12-800948-2.00001-7