Describe the extraocular muscles under the following heading
Origin
Insertion
Action
Nerve Supply
Clinical importance
INTRODUCTION
the movement and the position of eye is controlled by the extraocular muscles of the orbit that are attached to the eyeball and the boney orbit cavity. Some muscles of the eyeball are voluntary and some are involuntary
Voluntary muscles
the four rectus muscles( superior, lateral, medial , inferior rectus)
two oblique muscles(superior oblique and inferior oblique)
levator palpebrae superiors
Involuntary muscles
superior tarsal muscle
inferior tarsal muscle
orbitalis bridge
inferior orbital fissure
RECTI MUSCLES
origin
The four recti muscles arise form the common tendinous ring which is attached to the middle part of the superior orbital fissure. Although lateral rectus has an additional has an additional small tendinous head which arises from the middle part of the superior orbital fissure.
insertion
Recti are inserted into the sclera a little posterior to the limbus (corneoscleral junction)
actions
superior rectus - elevates at transverse axis
adducts at vertical axis
rotates the eyeball medially
inferior rectus - depresses at the transverse axis
adducts at the vertical axis
rotates the eyeball laterally
Medial rectus - adducts the eyeball in the vertical axis
Lateral rectus - Abducts the eyeball in the vertical axis
note: lateral rectus is the only recti muscle that abducts the eyeball in the ventromedial axis.
nerve supply
lateral rectus - abducent nerve.
remaining rectus muscles - oculomotor nerve
SUPERIOR OBLIQUE
origin
The superior oblique muscles arises from the undersurface of the lesser wing of sphenoid.
insertion
The tendon of superior oblique passes through a fibrocartilaginous pully and proceeds laterally downwards to insert into the sclera between the superior rectus and the lateral rectus.
action of superior oblique
depresses the eyeball at the transverse axis
abducts the eyeball in the vertical axis
facilitates medial rotation
nerve supply
the superior oblique is supplied by the trochlear nerve
INFERIOR OBLIQUE
origin
inferior oblique muscles arise from the undersurface of the lesser wing of sphenoid. lateral to the orbital groove.
insertion
It passes laterally upwards and backwards below the inferior rectus and the lateral rectus and inserts close to the superior oblique.
actions of inferior oblique muscle
elevates in the transverse axis.
abducts the eyeball
facilitates lateral rotation.
nerve supply - oculomotor nerve.
SINGLE MOVEMENT OF EYE
Elevators - inferior oblique
superior rectus
Depressors - superior oblique
inferior rectus
Adductors - medial rectus
superior rectus
inferior rectus
Abductors - inferior oblique
superior oblique
lateral rectus
intorters - superior oblique
superior rectus
extorters - inferior oblique
inferior rectus
CLINICAL SIGNIFICANCE
the weakness or the causes squint or strabismus, which may be concomitant or paralytic.
Concomitant squint is congenital and there is no limitation of movement
Paralytic squint is paralytic, movements are limited and head is turned in the direction of the function of paralytic muscle.
Nystagmus is the involuntary and rhythmical oscillatory movements of eyes due to incoordination of the oculomotor muscle.
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