Muscles - Extraocular

Question 1

Where are the extraocular muscles located? What is their general function.

Answer 1

They are extrinsic and separate from the eyeball itself. They control the movements of the eyeball and the superior eyelid.

Question 2

How many extraocular muscles are there?

Answer 2

7

• Levator palpabrae superioris (responsible for upper eyelid movement)
• Superior rectus
• Inferior rectus
• Lateral rectus
• Medial rectus
• Inferior oblique
• Superior oblique

Question 3

Attachment of levator palpabrae superioris?

Answer 3

Origin - Lesser wing of sphenoid bone, immediately above the optic foramen.

Insertion - superior tarsal plate of the upper eyelid (a think plate of connective tissue).

Question 4

Action of the levator palpabrae superioris?

Answer 4

Elevates the upper eyelid.

Question 5

Innervation of the levator palpabrae superioris?

Answer 5

Oculomotor (CN III)

The superior tarsal muscles is innervated by the sympathetic nervous system.

Question 6

Where do the recti muscles originate from characteristically?

Answer 6

The common tendinous ring - a ring of fibros tissue, which surrounds from the optic canal at the back of the orbit. The muscles then pass anteriorly to attach to the sclera of the eyeball.

Note ‘recti’ is derived from latin, meaning ‘straight’. They have a direct path from origin to attachment, in contrast to the oblique muscles that have an angular approach.

Question 7

Attachments of the superior rectus?

Answer 7

Origin - Superior part of the common tendinous ring.

Insertion - to the superior and anterior aspects of the sclera.

Question 8

Actions of the superior rectus?

Answer 8

Main - elevation

Secondary - adduction and medial rotation of the eyeball

Question 9

Innervation of the superior rectus?

Answer 9

Occulomotor nerve (CN III)

Question 10

Attachment of the inferior rectus?

Answer 10

Origin - inferior part of the common tendinous ring.

Insertion - inferior and anterior aspect of the sclera.

Question 11

Actions of the inferior rectus?

Answer 11

Main - depression

Secondary - adduction and lateral rotation of the eyeball.

Question 12

Innervation of the inferior rectus?

Answer 12

Oculomotor (CN III)

Question 13

Attachments of the medial rectus?

Answer 13

Origin - medial part of the common tendious ring.

Insertion - anteromedial aspect of the sclera.

Question 14

Actions of the medial rectus?

Answer 14

Adduction of the eyeball.

Question 15

Innervation of the medial rectus?

Answer 15

Occulomotor (CN III)

Question 16

Attachment of the lateral rectus?

Answer 16

Origin - lateral part of the common tendinous ring.

Insertion - anterolateral aspect of the sclera.

Question 17

Actions of the lateral rectus?

Answer 17

Abduction of the eyeball.

Question 18

Innervation of the lateral rectus?

Answer 18

Abducens nerve (CN VI).

Question 19

Attachments of the superior oblique?

Answer 19

Origin - Body of sphenoid bone.

Insertion - Its tendon passes through a trochlea and then attaches to the sclera, posterior to the superior rectus.

Question 20

Actions of the superior oblique?

Answer 20

Depresses
Abducts
Medially rotates

the eyeball

Question 21

Innervation of the superior oblique?

Answer 21

Trochlear nerve (CN IV)

Question 22

Attachments of the inferior oblique?

Answer 22

Origin - anterior aspect of the orbital floor.

Insertion - Sclera of the eye, posterior to the lateral rectus.

Question 23

Actions of the inferior oblique?

Answer 23

Elevates
Abducts
Laterally rotates

the eyeball

Question 24

Innervation of the inferior oblique?

Answer 24

Oculomotor nerve (CN III)

Question 25

Clinical relevance: Cranial nerve palsies

Answer 25

The extraocular muscles are innervated by three cranial nerves. Damage to one of the nerves will cause paralyis of its respective muscles. This will alter the resting gaze of the affected eye. Thus, a lesion of each cranial nerve has its own characteristic appearance:

• Occulomotor (CN III) - a lesion of this nerve affects most of the extraocular muscles. The affected eye is displaced laterally by the lateral rectus and inferiorly by the superior oblique. The eye adopts a position known as the ‘down and out’.
• Trochlear nerve (CN IV) - This will paralyse the superior oblique. There is no obvious effect of the resting orientation of the eyeball. However the patient will complain of diploplia (double vision), and may develop a head tilt away from the site of the lesion.
• Abducens nerve (CN VI) - a lesion of CN VI will paralyse the lateral rectus muscle. The affected eye will be adducted the resting tone of the medial rectus.