Extrinsic Ocular Muscles Flashcards
(8 cards)
EOM diagram
Top - superior rectus
Left - lateral rectus
Bottom - inferior rectus
Right - medial rectus
Top - superior oblique
Bottom - inferior oblique
Trochlea surrounds S.O
Lacrimal foramen - attached to inferior oblique
EOM x6 facts
6 muscles external to the eye.
Houses within the orbit.
Brings about rotation of the globe.
Proximal tendon anchored at periorbita.
Distal tendon blends into scleral storma.
Provides strong attachment to the eye.
EOM facts x4
4 rectus and superior oblique anchored at apex of orbit.
Run forward in a cone and surround and protect the optic nerve.
Inferior oblique originates at lateral edge of lacrimal foramen, passing underneath the eye with the orbital fasciae.
Helps support the eye in the orbit.
EOM features x4
Generally thinner than skeletal cells (10-15 nanometers diameter).
Cells extend full length of the muscle (up to 40mm)
Very active cells - rich blood supply.
High level nervous control compared to general skeletal muscle.
EOM function
To provide precise and co-ordinated eye movement, maintaining binocular vision.
EOM nervous system x4
1 motor neurone controls 3-10 muscle cells vs > 1000 in general skeletal.
En plaque endings - “fast twitch” fibres for rapid movement.
En grape endings - “tonic” fibres for smoother movements and hold point of fixation.
Extensive presence of feedback structures - proprioceptors
EOM measurements
Superior rectus to limbus - 7.5mm
Lateral rectus to limbus - 7.0mm
Inferior rectus to limbus - 6.5mm
Medial rectus to limbus - 5.5mm
EOM rectus muscles x4
4 rectus muscles share common origin at apex of orbit, the annulus of zinn.
Ring of tendon attached to the lesser wing of sphenoid bone, enclosing optical foramen.
Lateral expansion crosses superior orbital fissure and attaches to edge of greater wing of sphenoid.
Rectus muscles pass anteriorly from common origin, passing equator of eye to insertions where distal tendons blend with scleral stroma.
