EXTRAOCULAR MUSCLES Flashcards
SPIRAL OF TILLAUX
- rectus muscles pass through tenon’s capsule + insert into the sclera
- muscles insert at different distances from the cornea
- insertion pattern is a spiral with medial rectus closest to the cornea (5.5mm) + superior rectus furthest away (7.4mm)
TENON’S CAPSULE
- bulk of orbital fascial system
- forms envelope in which the eyeball moves
- fuses post. with optic nerve sheath
- fuses ant. with inter-muscular septum
ANNULUS OF ZINN
- ring of fibrous tissue surrounding optic nerve (ophthalmic artery + vein)
- all EOM arise from here except IO
- cone shaped structure behind eye
TROCHLEA
- loop of fibrous tissue that SO tendon passes through
- exerts pressure used in pulley system
ORIGIN OF INFERIOR OBLIQUE
behind lacrimal fossa
ORIGIN OF SUPERIOR OBLIQUE
lesser wing of sphenoid bone
SUPERIOR OBLIQUE CN
trochlear nerve (IV)
WHERE DO OBLIQUES INSERT INTO?
posterior aspect of sclera
THICK FIBRES
- striated muscle
- singly innervated
- motor end plate
- fast + slow twitch fibres
- all or none contraction
THIN FIBRES
- striated muscle
- multiply innervated (many branches, 1 nerve)
- en grappe end plate
- slow sustained (tonic)
- graded contraction
MOTION OF EYE
X axis - nasal -> temporal
Y axis - anterior -> posterior
Z axis - superior -> inferior
SACCADES
eye movement - quick jumps
SMOOTH TRACKING
combined head + eye tracking
WHAT INNERVATES THE LATERAL RECTUS?
abducens - cranial nerve VI
WHAT DOES CRANIAL NERVE III INNERVATE?
(oculomotor nerve)
- levator palpebrae
- superior rectus
- medial rectus
- inferior rectus
- inferior oblique
LEVATOR PALPEBRAE SUPERIORIS
- eyelid elevation
- originates above annulus of zinn
INFERIOR OBLIQUE
- EXTORSION
(abduction, elevation) - originates behind lacrimal fossa
SUPERIOR OBLIQUE
- INTORSION
(abduction, depression) - originates superior to annulus of zinn
- trochlear nerve
SLIM
superior - 7.4mm
lateral - 6.9mm
inferior - 6.7mm
medial - 5.5mm
WHAT MUSCLES ABDUCT?
- inferior oblique
- superior oblique
- lateral rectus
