The abducens nerve or abducent nerve, also known as the sixth cranial nerve, cranial nerve VI, or simply CN VI, is a cranial nerve in humans and various other animals that controls the movement of the lateral rectus muscle, one of the extraocular muscles responsible for outward gaze. It is a somatic efferent nerve.
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The oculomotor nerve, also known as the third cranial nerve, cranial nerve III, or simply CN III, is a cranial nerve that enters the orbit through the superior orbital fissure and innervates extraocular muscles that enable most movements of the eye and that raise the eyelid. The nerve also contains fibers that innervate the intrinsic eye muscles that enable pupillary constriction and accommodation. The oculomotor nerve is derived from the basal plate of the embryonic midbrain. Cranial nerves IV and VI also participate in control of eye movement.
In anatomy, the orbit is the cavity or socket/hole of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents. In the adult human, the volume of the orbit is 30 millilitres, of which the eye occupies 6.5 ml. The orbital contents comprise the eye, the orbital and retrobulbar fascia, extraocular muscles, cranial nerves II, III, IV, V, and VI, blood vessels, fat, the lacrimal gland with its sac and duct, the eyelids, medial and lateral palpebral ligaments, cheek ligaments, the suspensory ligament, septum, ciliary ganglion and short ciliary nerves.
The 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. It is the only extraocular muscle innervated by the trochlear nerve.
Duane syndrome is a congenital rare type of strabismus most commonly characterized by the inability of the eye to move outward. The syndrome was first described by ophthalmologists Jakob Stilling (1887) and Siegmund Türk (1896), and subsequently named after Alexander Duane, who discussed the disorder in more detail in 1905.
Eye movement includes the voluntary or involuntary movement of the eyes. Eye movements are used by a number of organisms to fixate, inspect and track visual objects of interests. A special type of eye movement, rapid eye movement, occurs during REM sleep.
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 (III). In the primary position, its primary function is elevation, although it also contributes to intorsion and adduction. It is associated with a number of medical conditions, and may be weak, paralysed, overreactive, or even congenitally absent in some people.
The inferior rectus muscle is a muscle in the orbit near the eye. It is one of the four recti muscles in the group of extraocular muscles. It originates from the common tendinous ring, and inserts into the anteroinferior surface of the eye. It depresses the eye (downwards).
The lateral rectus muscle is a muscle on the lateral side of the eye in the orbit. It is one of six extraocular muscles that control the movements of the eye. The lateral rectus muscle is responsible for lateral movement of the eyeball, specifically abduction. Abduction describes the movement of the eye away from the midline, allowing the eyeball to move horizontally in the lateral direction, bringing the pupil away from the midline of the body.
The medial rectus muscle is a muscle in the orbit near the eye. It is one of the extraocular muscles. It originates from the common tendinous ring, and inserts into the anteromedial surface of the eye. It is supplied by the inferior division of the oculomotor nerve (III). It rotates the eye medially (adduction).
The inferior oblique muscle or obliquus oculi inferior is a thin, narrow muscle placed near the anterior margin of the floor of the orbit. The inferior oblique is one of the extraocular muscles, and is attached to the maxillary bone (origin) and the posterior, inferior, lateral surface of the eye (insertion). The inferior oblique is innervated by the inferior branch of the oculomotor nerve.
The extraocular muscles, or extrinsic ocular muscles, are the seven extrinsic muscles of the human eye. Six of the extraocular muscles, the four recti muscles, and the superior and inferior oblique muscles, control movement of the eye and the other muscle, the levator palpebrae superioris, controls eyelid elevation. The actions of the six muscles responsible for eye movement depend on the position of the eye at the time of muscle contraction.
The nasociliary nerve is a branch of the ophthalmic nerve (CN V1) (which is in turn a branch of the trigeminal nerve (CN V)). It is intermediate in size between the other two branches of the ophthalmic nerve, the frontal nerve and lacrimal nerve.
The superior ophthalmic vein is a vein of the orbit that drains venous blood from structures of the upper orbit. It is formed by the union of the angular vein, and supraorbital vein. It passes backwards within the orbit alongside the ophthalmic artery, then exits the orbit through the superior orbital fissure to drain into the cavernous sinus.
The lacrimal nerve is the smallest of the three main branches of the ophthalmic nerve (CN V1) (itself a branch of the trigeminal nerve (CN V)).
The inferior ophthalmic vein is a vein of the orbit that - together with the superior ophthalmic vein - represents the principal drainage system of the orbit. It begins from a venous network in the front of the orbit, then passes backwards through the lower orbit. It drains several structures of the orbit. It may end by splitting into two branches, one draining into the pterygoid venous plexus and the other ultimately into the cavernous sinus.
The short posterior ciliary arteries are a number of branches of the ophthalmic artery. They pass forward with the optic nerve to reach the eyeball, piercing the sclera around the entry of the optic nerve into the eyeball.
Tenon's capsule, also known as the Tenon capsule, fascial sheath of the eyeball or the fascia bulbi, is a thin membrane which envelops the eyeball from the optic nerve to the corneal limbus, separating it from the orbital fat and forming a socket in which it moves.
The following outline is provided as an overview of and topical guide to human anatomy:
