Orbit and Cavernous Sinus - LO 7
7. What are the nerves that provide motor, sensory, and autonomic innervation to the orbit and its content?
Ophthalmic n. (V1) branches:
The frontal nerve is the largest branch of V1, and it afferently serves the medial upper eyelid (skin & conjunctiva), skin of the forehead, and frontal sinus mucosa. A prominent feature of the superior orbit, the frontal n. may be found superior to the levator palpebrae superioris m.
The frontal n. divides about midway through the orbit into the supra-orbital (lateral) and supratrochlear (medial) nn. The supratrochlear n. passes superior to the trochlea of the superior oblique m. to afferently serve the skin of the medial forehead, and skin and conjunctiva of the medial superior eye. The supra-orbital n. further divides into medial and lateral branches, which afferently serve the mucosa of the frontal sinus, skin of the lateral forehead, and skin and conjunctiva of the lateral superior eye. Branches of the supra-orbital n. may be seen exiting the cranium via the supra-orbital foramen or notch.
The lacrimal n. (V1) is the smallest branch of the ophthalmic n. The lacrimal n. enters the orbit through the superior orbital fissure, and may be found superior to the lateral rectus m., en route to the lacrimal gland.
The nasociliary n. branches from V1 in the superior orbital fissure. The nasociliary n. gives rise to:
long ciliary nn.,
anterior & posterior ethmoidal nn.,
infratrochlear n., and
a communicating branch to the ciliary ganglion transmitting afferent fibers from the eye via short ciliary nn.
The infratrochlear n. provides sensory innervation to conjunctiva, skin of eyelids, lacrimal caruncle and sac, and side of nose. This nerve can be seen exiting the orbit below the trochlea of the superior oblique m.
The anterior and posterior ethmoidal nn. exit through the anterior and posterior ethmoidal foramina, respectively.
The long ciliary nerves arise from the nasociliary n. (V1) in the vicinity of the optic n. (CN II). These branches carry afferent fibers from the eye and postganglionic sympathetic fibers to the dilator pupillae muscle of the eye.
Oculomotor n. (CN III)
The oculomotor n. (CN III) arises from the midbrain, travels within the lateral wall of the cavernous sinus, divides into superior and inferior divisions, and these divisions enter the orbit through the superior optic fissure (and also through the common anular tendon). The superior and inferior divisions are typically separated by the nasociliary n. (of V1) and the optic n. (CN II).
The superior division of oculomotor n. efferently innervates:
levator palpebrae superioris m., and
superior rectus m.
The inferior division of oculomotor n. efferently innervates:
medial rectus m.,
inferior rectus m.,
inferior oblique m., and
transmits preganglionic parasympathetic fibers to:
ciliary ganglion (for sphincter pupillae muscles and ciliary muscles)
Short cilary nn.
The short ciliary nn. transmit three types of fibers between the eye and the ciliary ganglion:
afferent fibers from the eye, through the ganglion, to the nasociliary n. (V1),
postganglionic parasympathetic fibers from the ganglion (preganglionics from oculomotor) to the ciliary muscles and sphincter pupillae muscles, and
postganglionic sympathetic fibers (from perivascular plexuses) to the intra-ocular vessels.
Ciliary ganglion
The ciliary ganglion is a peripheral parasympathetic ganglion for intra-ocular muscles, typically located on the lateral aspect of the optic n. (CN II) near the apex of the orbit. The ciliary ganglion has three conduits to/from the remainder of the PNS:
nasociliary n. (of V1) - transmits afferent fibers from the eye through the ganglion to the nasociliary n.,
oculomotor n. (CN III) - transmits preganglionic parasympathetic fibers to the ciliary ganglion, and
sympathetic - postganglionic sympathetic fibers are transmitted to (and through) the ciliary ganglion from perivascular plexuses of the internal carotid a. These fibers may also associate with the oculomotor n.
The ciliary ganglion communicates with the eye via the short ciliary nn.
Optic n. (CN II)
Optic n. (CN II) travels through the optic canal to enter the orbit and pierce the sclera. This is the most obvious structure in this area. This cranial nerve is special somatic afferent and functions in vision.
Abducens n. (CN VI)
The abducens n. (CN VI) arises from the brainstem, travels through the cavernous sinus, and enters the orbit through the superior orbital fissure (and also through the common anular tendon). The abducens n. innervates the lateral rectus m. (i.e. the ABDUCens ABDUCts the eye).
Trochlear n. (CN IV)
The trochlear n. (CN IV) is the smallest cranial nerve and the only nerve to arise from the dorsal aspect of the brainstem. The trochlear n. travels within the lateral wall of the cavernous sinus, enters the orbit through the superior orbital fissure, and travels along the medial wall of the orbit to innervate the superior oblique m. This nerve is generally easiest to locate running deep to the posterior-most aspect of the superior oblique m.
