Extraocular Muscles Flashcards
(19 cards)
What are the extraocular muscles (EOMs)?
The extraocular muscles are six muscles responsible for controlling eye movements. These include:
Medial rectus (MR)
Lateral rectus (LR)
Superior rectus (SR)
Inferior rectus (IR)
Superior oblique (SO)
Inferior oblique (IO)
What are the main functions of the extraocular muscles?
The extraocular muscles control the position and movement of the eyeball, including:
Adduction: Moving the eye toward the nose.
Abduction: Moving the eye away from the nose.
Elevation: Moving the eye upward.
Depression: Moving the eye downward.
Intorsion: Rotating the top of the eye toward the nose.
Extorsion: Rotating the top of the eye away from the nose.
Which cranial nerves innervate the extraocular muscles?
Lateral Rectus (LR): CN VI (Abducens) – controls abduction.
Superior Oblique (SO): CN IV (Trochlear) – controls intorsion.
Other EOMs (MR, SR, IR, IO): CN III (Oculomotor) – controls adduction, elevation, depression, and intorsion/extorsion.
What is the mnemonic to remember the cranial nerve innervation of the extraocular muscles?
LR6 SO4 (O3)
Lateral Rectus (abduction) = CN VI (Abducens)
Superior Oblique (intorsion) = CN IV (Trochlear)
Other muscles (MR, SR, IR, IO) = CN III (Oculomotor)
What is the origin and insertion of the Medial Rectus (MR)?
Origin: Common tendinous ring.
Insertion: Medial side of the eyeball.
Innervation: CN III (Oculomotor) (inferior division).
Action: Adduction (moves the eye towards the nose).
What is the origin and insertion of the Lateral Rectus (LR)?
A6:
Origin: Common tendinous ring.
Insertion: Lateral side of the eyeball.
Innervation: CN VI (Abducens).
Action: Abduction (moves the eye away from the nose).
What is the origin and insertion of the Superior Rectus (SR)?
Origin: Common tendinous ring.
Insertion: Superior aspect of the eyeball.
Innervation: CN III (Oculomotor) (superior division).
Action: Elevation, adduction, and intorsion (when the eye is looking straight ahead).
What is the origin and insertion of the Inferior Rectus (IR)?
Origin: Common tendinous ring.
Insertion: Inferior aspect of the eyeball.
Innervation: CN III (Oculomotor) (inferior division).
Action: Depression, abduction, and extorsion (when the eye is looking straight ahead).
What is the origin and insertion of the Superior Oblique (SO)?
Origin: Anterior orbital floor.
Insertion: Posterior lower lateral (temporal) quadrant of the eyeball.
Innervation: CN IV (Trochlear).
Action: Intorsion, depression, and abduction.
What is the origin and insertion of the Inferior Oblique (IO)?
Origin: Just outside the common tendinous ring.
Insertion: Upper lid, superior conjunctival fornix, lateral orbital tubercle, lacrimal crest.
Innervation: CN III (Oculomotor) (superior division).
Action: Elevation, extorsion, and abduction.
What is the role of the Levator Palpebrae Superioris muscle?
Action: Raises the upper eyelid.
Innervation: CN III (Oculomotor) (superior division).
What are the primary actions of the Superior Rectus (SR)?
Primary action: Elevation.
Secondary action: Intorsion.
Tertiary action: Adduction.
What are the primary actions of the Inferior Oblique (IO)?
Primary action: Extorsion.
Secondary action: Elevation.
Tertiary action: Abduction.
What is the mnemonic for remembering the actions of the Superior Rectus and Inferior Oblique?
RADSIN
R: Recti → A: Adduct.
S: Superior → I: Intort.
I: Inferior → N: Extort.
What does a motility test assess?
A motility test assesses the movement and coordination of the extraocular muscles (EOMs) and can detect abnormalities in eye movement that may indicate underlying neurological issues.
What is the common cause of anomalous motility?
Anomalous motility may be a sign of serious brain disease or neurological disorders, which require prompt clinical investigation.
How does the trochlea relate to the Superior Oblique (SO) muscle?
The trochlea is a pulley-like structure through which the Superior Oblique (SO) muscle passes, enabling its function in intorsion, depression, and abduction.
How is intorsion and extorsion defined in relation to eye movement?
Intorsion: Rotating the top of the eye toward the nose (e.g., by the Superior Rectus and Superior Oblique).
Extorsion: Rotating the top of the eye away from the nose (e.g., by the Inferior Rectus and Inferior Oblique).
Which extraocular muscle is responsible for abduction of the eye?
The Lateral Rectus (LR), innervated by CN VI (Abducens), is responsible for abduction (moving the eye away from the nose).
