Anatomy of the muscular system of the eye, External muscles of the eye
EXTRAOCULAR MUSCLES
There are six extraocular muscles in each eye which control their movements.
I. The Recti Muscles
The four recti muscles originate from the common annular tendon of Zinn situated around the optic foramen at the apex of the orbit.
The recti muscles are inserted into the sclera by flat tendons at various distances from the limbus
- Superior rectus—7.7 mm
- Lateral rectus—7 mm
- Inferior rectus—6.6 mm ▯ Medial rectus—5.5 mm.
II. The Oblique Muscles ▯ Superior oblique ▯ Inferior oblique.
Superior oblique m. arises from the upper and inner margin of the optic foramen. It runs forwards to the upper and inner angle of the orbit. It passes through the trochlea (a fibrous pulley) and is inserted into the upper and outer part of the sclera.
Inferior oblique originates from the floor of the orbit near the inferior orbital margin. It passes outwards below the inferior rectus muscle. It is inserted into the outer part of the sclera behind the equator.
Innervation of the extraocular muscles
LR6-SO4-R3
- Lateral Rectus is 6th CN
- Superior Oblique is 4th CN
- Rest are all 3rd CN
- Oculomotor nerve (3^{rd} Cranial nerve) o Superior rectus muscle o Inferior rectus muscle o Medial rectus muscle o Inferior oblique muscle.
- Trochlear (4th cranial nerve): Superior oblique muscle.
- Abducens (6th cranial nerve): Lateral rectus muscle.
Blood Supply
The blood supply is by the muscular branches of the ophthalmic artery.
Action of the Extraocular Muscles
The action of the extraocular muscles can be thus summarized as follows:
- All the recti muscles are Adductors except lateral rectus.
- Both the oblique muscle are Abductors.
- Both the superior muscles are intortors.
- Both the inferior muscles are extortors.
- a. Intorsion—When the upper pole of the cornea rotates nasally.
- b. Extorsion—When the upper pole of the cornea rotates temporally.