Nasociliary nerve
Encyclopedia
The nasociliary nerve is a branch of the ophthalmic nerve
Ophthalmic nerve
The ophthalmic nerve is one of the three branches of the trigeminal nerve, the fifth cranial nerve. The ophthalmic nerve carries only sensory fibers.-Branches:*Nasociliary nerve**sensory root of ciliary ganglion**posterior ethmoidal nerve...

. It is intermediate in size between the two other main branches of the ophthalmic nerve, the frontal nerve
Frontal nerve
The frontal nerve is the largest branch of the ophthalmic nerve, and may be regarded, both from its size and direction, as the continuation of the nerve....

 and the lacrimal nerve
Lacrimal nerve
The lacrimal nerve is the smallest of the three branches of the ophthalmic division of the trigeminal nerve.It sometimes receives a filament from the trochlear nerve, but this is possibly derived from the branch that goes from the ophthalmic to the trochlear nerve.It passes forward in a separate...

, and is more deeply placed.

Path

The nasociliary nerve enters the orbit between the two heads of the lateral rectus muscle
Lateral rectus muscle
The lateral rectus muscle is a muscle in the orbit. It is one of six extraocular muscles that control the movements of the eye and the only muscle innervated by the abducens nerve, cranial nerve VI....

s and between the superior and inferior rami of the oculomotor nerve
Oculomotor nerve
The oculomotor nerve is the 3rd of 12 paired cranial nerves. It enters the orbit via the superior orbital fissure and controls most of the eye's movements, including constriction of the pupil and maintaining an open eyelid by innervating the Levator palpebrae superiors muscle. The optic nerve is...

 (CN III). It passes across the optic nerve
Optic nerve
The optic nerve, also called cranial nerve 2, transmits visual information from the retina to the brain. Derived from the embryonic retinal ganglion cell, a diverticulum located in the diencephalon, the optic nerve doesn't regenerate after transection.-Anatomy:The optic nerve is the second of...

 (CN II) and runs obliquely beneath the superior rectus muscle
Superior rectus muscle
The superior rectus muscle is a muscle in the orbit. It is one of the extraocular muscles. It is innervated by the superior division of the oculomotor nerve...

 and superior oblique muscle
Superior oblique muscle
For the abdominal muscle see: Abdominal external oblique muscleThe superior oblique muscle, or obliquus oculi superior, is a fusiform muscle originating in the upper, medial side of the orbit which abducts, depresses and internally rotates the eye...

 to the medial wall of the orbital cavity. It passes through the anterior ethmoidal opening as the anterior ethmoidal nerve and enters the cranial cavity just above the cribriform plate of the ethmoid bone. It supplies branches to the mucous membrane of the nasal cavity and finally emerges between the inferior border of the nasal bone and the side nasal cartilages as the external nasal branch.

Tests

Since the long ciliary nerves carry the afferent limb of the corneal blink reflex, one can test the integrity of the nasociliary nerve (and, ultimately, the trigeminal nerve
Trigeminal nerve
The trigeminal nerve contains both sensory and motor fibres. It is responsible for sensation in the face and certain motor functions such as biting, chewing, and swallowing. Sensory information from the face and body is processed by parallel pathways in the central nervous system...

) by examining this reflex in the patient. Normally both eyes should blink when either conjuntiva is irritated. If neither eye blinks, then either the ipsilateral nasociliary nerve is damaged, or the facial nerve
Facial nerve
The facial nerve is the seventh of twelve paired cranial nerves. It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity...

 (CN VII, which carries the efferent limb of this reflex) is bilaterally damaged. If only the contralateral eye blinks, then the ipsilateral facial nerve is damaged. If only the ipsilateral eye blinks, then the contralateral facial nerve is damaged.

Branches

The nasociliary nerve gives off the following branches:
  • posterior ethmoidal nerve
    Posterior ethmoidal nerve
    The posterior ethmoidal nerve is a branch of the nasociliary nerve.It passes through the posterior ethmoidal foramen, with the posterior ethmoidal artery.It carries sensory information from the sphenoid sinus and posterior ethmoidal air cells....

  • long ciliary nerves
  • infratrochlear nerve
    Infratrochlear nerve
    The infratrochlear nerve is given off from the nasociliary just before it enters the anterior ethmoidal foramen.It runs forward along the upper border of the medial rectus, and is joined, near the pulley of the superior oblique, by a filament from the supratrochlear nerve.It then passes to the...

  • communicating branch to the ciliary ganglion (long root of the ciliary ganglion)
  • anterior ethmoidal nerve
    Anterior ethmoidal nerve
    The anterior ethmoidal nerve is a nerve which provides sensory branches to the nasal cavity. The nerve is the continuation of the Nasociliary nerve after it enters the anterior ethmoidal foramen into the anterior ethmoidal air cells. The nasociliary nerve arises from the Ophthalmic division of...



PLICA is a mnemonic often used to remember these branches.

External links

- "A deeper dissection of the right orbit from a superior approach."
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