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
