EXTRAOCULAR MUSCLES

INTRODUCTION:
  • The motor units are small, with only from 5 to 18 muscle fibers contact by each motor nerve.
  • Anteroposterior stability of eyeball is provided by Superior oblique,Superior rectus & Orbital fat.
  • The extraocular muscles develop along with Tenon's capsule (part of the ligaments) and the fatty tissue of the eye socket (orbit)
TYPES OF EXTRAOCULAR MUSCLES
  • VOLUNTARY MUSCLES
  1. Levator palpebrae superioris: Superior most muscle in the orbit.(Has voluntary and involuntary parts).
  2. Superior rectus:Its's Yoke muscle will be contralateral side of inferior rectus.Makes<230with anatgonis axiinferioripsilateralmedialmuscleobliqu oforbitalrectus:liesrectus rectus rectus sidesuperior superiorto synergistic to with">
  3. Lateral rectus
  4. Superior oblique:Longest and thinnest intraorbital muscle, the muscle ends before the trochlea, tendon is 2.5 cm, smooth movement through trochlea.Makes
  5. Orbitalis.
MUSCLES ORIGIN INSERTION NERVE SUPPLY ACTION
Levator palpebrae superioris Inferior surface of lesser wing of sphenoid Upper lamina-Anterior surface of superior tarsus and skin of upper eyelid
Middle lamina-superior margin of superior tarsus
Lower lamina-Superior conjunctival fornix
Upper division of occulomotor nerve Elevation of upper eyelid
Superior rectus Superior part of common tendon of zinn sclera by flat tendinous insertion(10mm broad)about 7.7 mm behind sclero-corneal junction superior division of occulomotor nerve Elevation
Rotation about the vertical axis toward midline
Adduction
Torsion nasally Intorsion.
Inferior rectus Inferior part of common tendon of zinn sclera 6.5 mm behind limbus/sclero corneal junction Inferior division occulomotor nerve Primary depressor
Subsidiary actions are adduction and extorsion
Medial rectus Annulus of zinn and from optic nerve sheath sclera 5.5mm behind sclero-corneal junction lower division of occulomotor nerve Adductor of the eye
Lateral rectus Annulus of zinn sclera 6.9mm behind sclerocorneal junction. Abducent nerve Primary abductor of eye
Superior oblique Body of sphenoid above & medial to optic canal.
Passes along superomedial part of orbit & ends in a tendon.(does not arrises from annulus)
Posterosuperior quadrant of sclera behind equator of eyeball trochlear nerve Primary action-intorsion.
Subsidiary actions-abduction and depression.
Adducted position-depression
Inferior oblique posteroinferior surface of globe near the macula Inferior division of occulomotor nerve Primary action-extorsion.
Subsidiary actions-elevations and abduction.
Causes elevation only in adducted position of eyeball
BLOOD SUPPLY:
  1. Ophthalmic artery
  2. Medial muscular branch-inferior rectus, inferior oblique, medial rectus
  3. Lateral muscular branch-superior rectus, superior oblique, lateral rectus.
MOVEMENTS OF EYE:
MUSCLE ACTION IN PRIMARY POSITION ACTION IN ABDUCTED EYE ACTION IN ADDUCTED EYE
Superior oblique Depression
Abduction
Intortion
Intortion Depression
Inferior oblique Elevation
Abduction
Extortion
Extortion Elevation
Inferior rectus Depression
Adduction
Extortion
Depression Extortion
Superior rectus Elevation
Adduction
Intortion
Elevation Intortion
Adduction - -
Lateral rectus Abduction - -
Exam Question
  • Superior oblique rotates the eye downward and away from midline.
  • All the extra ocular muscles except inferior oblique arise from the apex of orbit.
  • Anteroposterior stability of eyeball is provided by Superior oblique,Superior rectus & Orbital fat.
  • Superior oblique:Longest and thinnest intraorbital muscle
  • Superior oblique muscle is involved in intorsion, depression and abduction of the eyeball
  • The superior oblique muscle is supplied by trochlear nerve
  • Superior rectus is supplied by superior division ofocculomotor nerve.
  • Inferior rectus inserts 6.5 mm behind limbus
  • Inferior rectus Lies inferior to inferior obli
  • que muscle
  • Inferior rectus is antagoinst to superior rectus
  • Inferior oblique is supplied by 3rd cranial nerve
  • Lateral rectus, Superior oblique are not supplied by occulomotor nerve
  • Downward and lateral gaze is action of superior oblique
  • Inferior oblique is the shortest extraocular muscle
  • The possterior end of inferior oblique Muscle Lies Near macula.
  • Yoke muscle of rt. superior Rectus will be lt. inferior rectus
  • The muscle which makes an angle of about 51° with the optical axis is superior oblique
  • The muscle which makes an angle of about 23° with the optical axis is Superior rectus
  • Lateral rectus is supplied by abducent nerve
  • Action of superior rectus is elevtaion Adduction and intortion
  • The extraocular muscles that does not arise from annulus is superior oblique
  • Muscle responsible for intorsion of the eye are superior oblique & superior rectus
  • Primary action of inferior oblique muscles are Elevation,Abduction & Extortion
Don't Forget to Solve all the previous Year Question asked on EXTRAOCULAR MUSCLES