Muscles - Extraocular Flashcards
Where are the extraocular muscles located? What is their general function.
They are extrinsic and separate from the eyeball itself. They control the movements of the eyeball and the superior eyelid.
How many extraocular muscles are there?
7
- Levator palpabrae superioris (responsible for upper eyelid movement)
- Superior rectus
- Inferior rectus
- Lateral rectus
- Medial rectus
- Inferior oblique
- Superior oblique
Attachment of levator palpabrae superioris?
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).
Action of the levator palpabrae superioris?
Elevates the upper eyelid.
Innervation of the levator palpabrae superioris?
Oculomotor (CN III)
The superior tarsal muscles is innervated by the sympathetic nervous system.
Where do the recti muscles originate from characteristically?
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.
Attachments of the superior rectus?
Origin - Superior part of the common tendinous ring.
Insertion - to the superior and anterior aspects of the sclera.
Actions of the superior rectus?
Main - elevation
Secondary - adduction and medial rotation of the eyeball
Innervation of the superior rectus?
Occulomotor nerve (CN III)
Attachment of the inferior rectus?
Origin - inferior part of the common tendinous ring.
Insertion - inferior and anterior aspect of the sclera.
Actions of the inferior rectus?
Main - depression
Secondary - adduction and lateral rotation of the eyeball.
Innervation of the inferior rectus?
Oculomotor (CN III)
Attachments of the medial rectus?
Origin - medial part of the common tendious ring.
Insertion - anteromedial aspect of the sclera.
Actions of the medial rectus?
Adduction of the eyeball.
Innervation of the medial rectus?
Occulomotor (CN III)
Attachment of the lateral rectus?
Origin - lateral part of the common tendinous ring.
Insertion - anterolateral aspect of the sclera.
Actions of the lateral rectus?
Abduction of the eyeball.
Innervation of the lateral rectus?
Abducens nerve (CN VI).
Attachments of the superior oblique?
Origin - Body of sphenoid bone.
Insertion - Its tendon passes through a trochlea and then attaches to the sclera, posterior to the superior rectus.
Actions of the superior oblique?
Depresses
Abducts
Medially rotates
the eyeball
Innervation of the superior oblique?
Trochlear nerve (CN IV)
Attachments of the inferior oblique?
Origin - anterior aspect of the orbital floor.
Insertion - Sclera of the eye, posterior to the lateral rectus.
Actions of the inferior oblique?
Elevates
Abducts
Laterally rotates
the eyeball
Innervation of the inferior oblique?
Oculomotor nerve (CN III)
Clinical relevance: Cranial nerve palsies
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.
