The Extrinsic and Intrinsic Muscles  of the Eye

Definition
Extrinsic muscles = situated outside the eye ball = Extraocular muscles
Intrinsic muscles = situated inside the eye ball = Intraocular muscles
Striated

Extrinsic or extraocular muscles
Six
attached to the eye ball and the walls of the orbital cavity
Four straight (rectus)
Two Oblique

medial rectus                           superior oblique
lateral rectus                            inferior oblique
superior rectus
inferior rectus

Movements & Nerve supply
Looking in a particular direction - voluntary
Coordination, convergence, accomodation - autonomic control

Lateral rectus - rotates the eyeball outwards        --   Abducent nerve (6th cranial nerve)
Medial rectus - rotates the eyeball inwards           --        Oculomotor nerve (3rd)
Superior rectus - rotates the eyeball upwards      --        Oculomotor nerve (3rd)
Inferior rectus - rotates the eyeball downwards    --        Oculomoter nerve (3rd)
Inferior oblique - rotates the eyeball upwards and outwards  ... Oculomotor nerve                                                                                                                       (3rd)
Superior oblique - rotates the eyeball downwards and outwards--Trochlear nerve    (4th)

        Intrinsic or intraocular muscles
Ciliary muscle - part of the ciliary body
Non-striated muscle
Attached through the suspensory ligament to the lens capsule
Changes the thickness of the lens
Accommodation is the main function
Iris
Iris has non-striated muscle fibres which constric and dilate the pupil and regulate the amount of light entering the eye.

Applied Anatomy
Extrinsic muscles - paralysis - squint (strabismus)
Ciliary muscles - weakness of accommodation in old age - presbyopia













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Muscle Name                Function                                                            Cranial Nerve Associated With Muscle
Superior Rectus       Rotates eye upward and towards midline                    Oculomotor nerve III
Inferior Rectus         Rotates eye downward and towards midline               Oculomotor nerve III
Medial Rectus          Rotates eye toward midline                                           Oculomotor nerve III
Lateral Rectus          Rotates eye away from midline                                    Abducens nerve VI
Superior Oblique     Rotates eye ownward and away from midline            Trochlear nerve IV
Inferior Oblique       Rotates eye upward and away from midline                Oculomotor nerve III

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