Extraocular and Intraocular Muscles
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The extraocular muscles include the orbicularis oculi, levator palpebrae superioris, four rectus and two oblique muscles, totaling eight. The four rectus muscles have a common origin from an oval ring at the apex of the orbit called the annulus of Zinn, which encompasses the optic foramen at the back and the wider medial part of the superior orbital fissure. The ring has an upper and a lower tendon. The upper part supplies origin to part of the medial and lateral recti and the whole of the superior rectus. The lower part provides origin to part of the lateral and medial recti and the whole of the inferior rectus.
KeywordsExtraocular and intraocular muscles Four recti Two obliques Levator palpebrae superioris Orbicularis oculi Blinking reflex Unstriated involuntary muscles Cervical sympathetic Primary action Subsidiary action Neuromuscular control
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