Muscles of orbit

There are seven muscles of the orbit; one controlling the movement of the upper eyelid, and six others controlling the movement of the eyes.

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Muscle

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Innervation

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Primary function

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Secondary function

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Tertiary function

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Levator palpebrae superioris

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Oculomotor nerve

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Elevation of the superior (upper) eyelid

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Superior rectus

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Oculomotor nerve

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Elevation

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Intorsion

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Adduction

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Inferior rectus

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Oculomotor nerve

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Depression

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Extorsion

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Adduction

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Lateral rectus

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Abducens nerve

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Abduction

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Medial rectus

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Oculomotor nerve

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Adduction

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Superior oblique

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Trochlear nerve

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Intorsion

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Depression

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Abduction

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Inferior oblique

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Oculomotor nerve

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Extorsion

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Elevation

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Abduction

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A good mnemonic to remember which muscles are innervated by what nerve is to paraphrase it as a molecular equation: LR6SO4R3.

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Lateral Rectus - Cranial Nerve VI,

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Superior Orbital - Cranial Nerve IV,

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the Rest of the muscles - Cranial Nerve III.

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Another way to remember which nerves innervate which muscles is to understand the meaning behind all of the Latin words. The fourth cranial nerve, the trochlear, is so named because the muscle it innervates, the superior oblique, runs through a little fascial pulley that changes its direction of pull. This pulley exists in the superiomedial corner of each orbit, and "trochl-" is Latin for "pulley." The sixth cranial nerve, the abducens, is so named because it controls the lateral rectus, which abducts the eye (rotates it laterally) upon contraction. All of the other muscles are controlled by the third cranial nerve, the oculomotor, which is so named because it is in charge of the movement (motor) of the eye (oculo-).

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