Trigeminal Nerve - Cranial Nerve V/5

Introduction

• It is the largest cranial nerve.
• It divides into 3 nerve branches.

Functions in General (just to be oriented with the nerve. More detail below.):

• GSA (general sensory afferent/general somatic sensory):  sensory input from the head, ear and the dura mater.
• BE (branchial efferent AKA visceral motor AKA muscles derived from pharyngeal arches):  the muscles of mastication, the tensor tympani, the tensor veli palatini, the mylohyoid, and the anterior belly of the digastric.

Nuclei of Trigeminal Nerve in Brainstem

Nuclei of Trigeminal nerve are not confined to a specific part of the brainstem (such as only pons, or only the medulla) but are along the entire length of pons & medulla.

Figure 1: Trigeminal nerve nuclei approximate location in brainstem and relation to each other - longitudinal view

Figure 2: Location of Nuclei of Trigeminal Nerve in Brainstem and 
relation to each other - posterior view

Figure 3: Location of Nuclei of Trigeminal Nerve in Brainstem and 

relation to each other - longitudinal view

Sensory nuclei:

1. Main sensory nucleus: fibers carrying touch and pressure sensations end here.
2. Mesencephalic nucleus: fibers carrying proprioception from muscles supplied by the trigeminal nerve (muscles of mastication…etc.) end here.
3. Spinal nucleus: fibers carrying pain and temperature end here. 

Motor nuclei:

1. Motor nucleus: 
1. Receives corticonuclear(AKA corticobulbar) fibers from the precentral gyrus of the cerebral cortex of both hemispheres. 
2. Receives fibers from other brainstem nuclei.
3. Receives fibers from the mesencephalic nucleus thereby forming a reflex arc. 

Emerges from brainstem

• The trigeminal nerve has 2 roots that emerge together from the brainstem: one big sensory root and one small motor root. 
• These roots emerge from the anterior part of the pons. 

Figure 4: Trigeminal Nerve root emerging from brainstem - anterior view

Route

Figure 5: Trigeminal Nerve exit/entry from/to cranial cavity

1. After emerging from the pons, the roots continue anteriorly from the posterior cranial fossa to the middle cranial fossa by passing over the petrous temporal bone
2. The roots then reach the anterior part of the petrous temporal bone. 
1. At this point, the sensory root expands into the trigeminal ganglion. 
2. The motor root continues beside it without passing through the ganglion.
• Trigeminal ganglionWhat is it? The trigeminal ganglion is analogous to the spinal ganglion. It contains cell bodies for the sensory neurons of the trigeminal nerve.
  Where is it? It is located in a depression called the trigeminal depression on the anterior wall of the petrous bone.
  Note: the motor root of the trigeminal nerve is completely separate from the ganglion. It runs by the ganglion but does not pass through it as the trigeminal ganglion is purely for sensory neurons cell bodies.
3. Three nerve branches arise from the anterior border of the trigeminal ganglion: Ophthalmic branch, Maxillary branch and Mandibular branch.
1. Till here, these nerve branches are all sensory. 
2. What about the motor root that passed beside the ganglion? At this point, it continues as the motor root and is still separate from the 3 sensory roots. 

Opening in skull through which nerves pass

Nerve	Passes through Opening	To enter
Ophthalmic division (V1) of V	1.     Superior orbital fissure	Orbit
Maxillary division (V2) of V	2.     Foramen rotundum	Pterygopalatine fossa then inferior orbital fissure
Mandibular division (V3) of V	3.     Foramen ovale	Infratemporal fossa

Figure 6: Side view of internal cranial cavity showing openings in the skull through which Trigeminal nerve branches pass

Each branch passes through a different opening in the skull. 

1. V1: Ophthalmic branch passes through the cavernous sinus – in the lateral wall of the sinus above the maxillary nerve Fig. 7 – on its way to exit through the superior orbital fissure.

2. V2: Maxillary branch also passes through the cavernous sinus the most inferior structure in the lateral wall of the sinus Fig. 7 – on its way to exit through the foramen rotundum

Figure 7: Trigeminal Nerve location in cavernous sinus in relation to other structures

Figure 8: Cavernous sinus location inside skull

3. V3: Mandibular branch passes immediately through the foramen ovale.
4. Motor root: passes with the Mandibular branch through the foramen ovale. After exiting the foramen ovale it unites with the Mandibular nerve to form one nerve – still called Mandibular nerve. (Strange considering scientists love to name each part of a something differently especially when things merge together).

This means that the Mandibular nerve is the only trigeminal branch that has a motor component.

Figure 9: Side view of Trigeminal Nerve branches location and distribution

Figure 10: Trigeminal ganglion and relation to Trigeminal nerves

Thus:

1. 1. V1 – Ophthalmic branch: sensory fibers
2. 2. V2 – Maxillary branch: sensory fibers
3. 3. V3 – Mandibular branch: sensory fibers and motor fibers.

Branches

V1: Ophthalmic branch

Branches:

1. Lacrimal nerve:

Supplies?

• Lacrimal gland (for that time when we are watching The Notebook and we need tears to spill down)
• Sensory to conjunctiva and skin of upper eyelid
• Postganglionic parasympathetic secretomotor fibers: these fibers are from the Zygomaticotemporal nerve which is a branch of the Maxillary nerve. They are originally from the facial nerve though. (check Ptergopalatine ganglion post)

 NOTE: it is for this reason, in a lesion of the Ophthalmic nerve that you get loss of corneal reflex. The lacrimal nerve supplies the conjunctiva of the eye which if affected by an Ophthalmic nerve lesion would not convey the impulses when a cotton touches the eye. So a person would not blink when a cotton ball touches the eyeball.

2. Frontal:

Further branches?

These branches leave the orbital cavity to ascend to the forehead:

• supraorbital nerve
• supratrochlear nerve

Supplies?

• frontal air sinus
• skin of forehead and scalp

NOTE: thus a lesion of the Ophthalmic nerve would cause not only loss of corneal reflex but loss of upper facial sensation.

3. Nasociliary:

Where does it run?

• On the upper border of medial rectus muscle
• Enters anterior ethmoidal foramenenters cranial cavityexits through a slit beside the crista gallienters nasal cavity.
• Changes its name to anterior ethmoidal nerve as soon as it enters cranial cavity.

Branches in the eye and the supply of each branch?

• Sends sensory fibers to ciliary ganglion
• Long ciliary nerves  supply sympathetic to dilator pupillae muscle and sensory to cornea
• Infratrochlear nerve supplies sensory to skin of eyelids

Branches in ethmoid?

• Posterior ethmoidal nerve  supplies sensory to ethmoid and sphenoid sinuses

Branches in nose?

• Internal nasal branches
• External nasal branches  supplies sensory to skin of tip of nose

V2: Maxillary branch

It continues as the Infraorbital nerve as it passes through the infraorbital canal.

Figure 11: Branches of the maxillary nerve

Where does it run?

• Ganglionic branches: after entering pterygopalatine fossa it gives off branches to the pterygopalatine ganglion.
• Zygomatic branch: after entering inferior orbital fissure it gives off zygomatic nerve which divides into:
• Zygomaticotemporal nerve: supplies skin of face, transports parasympathetic secretomotor fibers of facial nerve to lacrimal gland
• Zygomaticofacial nerve: supplies skin of face
• Posterior superior, Middle superior and Anterior superior alveolar nerves from the infraorbital nerve: supplies middle region of face, nasal mucosa, maxillary sinus, palate, upper teeth & gums 

NOTE: thus a lesion of the Maxillary nerve causes loss of sensation from middle of face & upper jaw. 

V3: Mandibular branch

• Is the nerve of the 1^st pharyngeal (AKA branchial) arch.
• Divides into anterior and posterior divisions

Branches of main trunk (supply)?

• Meningeal branch: enters  through the foramen spinosuminto the middle cranial cavitysupplies the dura mater and mastoid cells
• Nerve to medial pterygoid muscle: supplies medial pterygoid muscle, tensor veli palatini

Branches of anterior division?

NOTE: all branches are motor except one – buccal nerve.

• Masseteric nerve: supplies masseter muscle
• Deep temporal nerves: supplies temporalis muscle
• Nerve to lateral pterygoid muscle: supplies lateral pterygoid muscle
• Buccal nerve: supplies sensory to mucous membranes of cheek

Branches of posterior division?

NOTE: all branches are sensory except one – the mylohoid nerve. “poSterior is Sensory”

• Auriculotemporal nerve (skin of auricle, external auditory meatus, temporomandibular joint, scalp, parasympathetic fibers to parotid salivary gland)
• Lingual nerve: 
• Joins fibers from the Chorda Tympani
• Its sensory supply is: 
• General sensation (general somatic afferent) from Lingual nerve fibers for the anterior 2/3 of tongue and floor of oral cavity.
• Fibers from the Chorda Tympani nerve (from the Facial nerve-CNVIII) carry:
• Special visceral afferent sensation carried is the taste from the anterior 2/3 of tongue. (do not pass through ganglion)
• Preganglionic parasympathetic secretomotor to the submandibular ganglion. These presynaptic fibers synapse with postganglionic parasympathetic fibers in the ganglion. The parasympathetic fibers then leave the ganglion to either:
• Supply the submandibular and sublingual glands straight away.
• Or re-enter the lingual nerve and from there are distributed to the submandibular and sublingual glands.
• Inferior alveolar nerve:
• Mylohyoid nerve: supplies the mylohyoid muscle
• Communicating branch: from inferior alveolar nerve to lingual nerve (of the anterior division)
• It then enters the Mandibular canal: supplies lower jaw and teeth
• Then it emerges from the mental foramen: supplies the skin of the chin

References

Drake, R., Vogl, A., & Mitchell, A. (2010). Chapter 8: Head and neck - orbit. Gray's anatomy for students (2nd ed., pp. 878-902). Philadelphia: USA: Elsevier: Churchill Livingstone.

Snell, R. (2010). The cranial nerve nuclei and their central connections and distribution. Clinical neuroanatomy (7th ed., pp. 331-370). Philadelphia: Lippincott Williams and Wilkins.

Snell, R. (2007). Chapter 18: The eye and the ear. Clinical anatomy by systems (pp. 657-685). Philadelphia: USA: Lippincott Williams & Wilkins.

Picture references

1. Done by me
2. By Gray696.png: User:mcstrother derivative work: Mcstrother (Gray696.png) [Public domain], via Wikimedia Commons / retouched from original
3. Brainstem Nuclei of Cranial Nerves
4. Done by me
5. CN V. Trigemninal Nerve fromm Stritch School of Medicine/retouched from original
6. Unknown (if you know source please message me so I can mention it) / retouched from original
7. Henry Gray (1918) Anatomy of the Human Body from Wikimedia Commons
8. By Anatomist90 (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons  / retouched from original
9. Struck on the face out of the blue from The Sunday Times
10. Done by me
11. Class presentation