Extraocular Muscles Ocular Anatomy
Exam 3
What are the two types of muscles of the globe and what do they control? -
ANS-Involuntary and voluntary.
Involuntary- located within the eye, controls movement of internal ocular structures
(ciliary muscle, iris sphincter and dilator)
Voluntary- attached to the sclera, control movement of the globe and six EOMs
What are the characteristics of extraocular muscles (EOMs)? - ANS-Have a denser
blood supply
Connective tissue sheaths are more delicate
Richer in elastic fibers than in skeletal muscle
Fewer muscle fibers in a motor unit
Dense innervation- for fine motor control, needed for high velocity and accurate eye
movements
Range of fiber sizes
Fibers closer to the surface have smaller diameters
Deeper fibers have larger diameters
Divided into groups based on location, size, morphology, and neuromuscular junction
type.
What are the types of fibers present in extraocular muscles and how do they differ? -
ANS-Twitch and slow
Twitch- fast movements
Slow- slower movements
What are the six EOMs ? Name the muscle which is the longest and the one which is
shortest. - ANS-MR, LR, SR, IR, SO, IO
Superior oblique = longest
Inferior rectus = shortest
What is annulus of Zinn? - ANS-A common tendinous ring that serves as an origin point
for 4 rectus muscles
What are the origins of the four rectus muscles on the annulus of Zinn? - ANS-MR and
LR- from upper and lower limb
SR- from upper limb
, IR- from lower limb
MR and SR- attach to the dural sheath of the optic nerve
What is occulomotor foramen and give its significance? - ANS-The area enclosed by the
tendinous ring. This is where several blood vessels and nerves pass through.
What is the tendon length and the distance from limbus of the 4 rectus muscles? -
ANS-MR: length = 3.7mm, distance = 5.5mm
LR: length = 8.8mm, distance = 6.9mm
SR: length = 5.8mm, distance = 7.7mm
IR: length = 5.5mm, distance = 6.5mm
What is Spiral of Tillaux? Give its origin and termination point - ANS-A line connecting
the rectus muscle insertions.
Starts at the medial rectus (closest to limbus), proceeds to the inferior, lateral and finally
superior rectus.
What is the largest EOM? - ANS-Medial rectus
What is the origin of medial rectus muscle, its insertion with respect to limbus and what
is the position of the insertion line? - ANS-Originates from upper and lower parts of
annulus and dural sheath of optic nerve.
Inserts closest to the limbus.
Insertion line lies vertically.
What is the origin and insertion of lateral rectus muscle? - ANS-Originates from upper
and lower limbs of annulus and from spina recti lateralis
Inserts parallel to medial rectus
What is spina recti lateralis? - ANS-A prominence on the greater wing of the sphenoid
bone.
What is the origin, insertion with respect to limbus and line of insertion of superior rectus
muscle? - ANS-Originates from upper limb of annulus and dural sheath of optic nerve
Insertion is farthest from the limbus
Line of insertion is oblique, the nasal side is closer to the limbus than the temporal side
What is the origin and how is the line of insertion of inferior rectus muscle? -
ANS-Originates from the lower limb of the annulus
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