Eye Muscles Flashcards
What is the role of intrinsic muscles on the eye?
Control pupil diameter
Alters lens curvature to allow us to see close objects
What is the role of extrinsic muscles on the eye?
Move the eye
What helps give the eyeball its shape?
Fat behind the eye
How many cranial nerves go to the eye and what type of innervation do they supply?
3 cranial nerves give both parasympathetic and sympathetic innervation
What are the 4 straight muscles (recti) of the eye?
Medial rectus
Lateral rectus
Inferior rectus
Superior
What are 2 oblique muscles of the eye?
Superior oblique
Inferior oblique
Where do the recti muscles arise from?
Apex of the orbit from an annular fibrous ring
Where does the superior oblique muscle arise from?
Roof of the orbit (posteriorly)
Where does the inferior oblique arise from?
Floor of the orbit (anteriorly)
What structure does the superior oblique attach to?
Trochlea
What does the inferior oblique do?
Acts as a hammock under the eye for support
What is the levator palpebrae superioris?
A muscle that goes to the upper eyelid to elevate it
Where do the recti muscles insert?
Sclera posteriorly
Where does the superior and inferior oblique insert?
Sclera posteriorly
What is the origin of the LPS?
Roof of orbit
What is the origin of recti muscles?
Tendinous ring
What is the origin of the superior oblique?
Lesser wing of sphenoid
What is the origin of the inferior oblique?
Medial part of orbit floor
What does the trochlear nerve supply?
Muscles attached to trochlea = superior oblique
What do the abducent nerve supply?
Muscle which abducts = lateral rectus
What does the oculomotor nerve supply?
Everything but the SO and LR
What movement occurs when a person looks up?
Elevation
What movement occurs when a person looks down?
Depression
What movement occurs if right eye looks left?
Adduction
What movement occurs if right eye looks right?
Abduction
What movement occurs when the eyes focus on something close up?
Convergence
What movements occur with head tilting?
Intorsion and extorsion
What is intorsion?
When the top of the eyeball rotates towards the nose
What is extorsion?
When the top of the eyeball rotates away from the nose
What is the action of the medial rectus?
Adduction
What is the action of the lateral rectus?
Abduction
What are the actions of the superior rectus?
Elevation
Adduction
Intorsion
What are the actions of the inferior rectus?
Depression
Adduction
Extorsion
What are the actions of the superior oblique?
Intorsion
Depression
Abduction
What are the actions of the inferior oblique?
Extorsion
Elevation
Abduction
What is esotropia?
Manifest convergent squint
What is exotropia?
Manifest divergent squint
What is stabismus?
Misalignment of the eyes
What is amblyopia?
Lazy eye
Brain suppresses image of one eye - leads to poor vision in affected eye
No pathology
What is diplopia?
Double vision
Occurs in squints that occur from nerve palsies
What are the intrinsic eye muscles?
Ciliaris muscle
Constrictor pupillae
Dilator pupillae
Where is the ciliaris muscle found?
In the ciliary body
Where is the constrictor pupillae found?
In the iris at pupillary border
Where is the dilator pupillae found?
Radially running muscle in iris
What intrinsic muscles receive parasympathetic innervation?
Ciliaris
Constrictor pupillae
Which intrinsic muscle receives sympathetic innervation?
Dilator pupillae
What pupillary reaction occurs with increased illumination?
Parasympathetic innervation causes pupils to constrict
What pupillary reaction occurs with decreased illumination?
Sympathetic innervation causes pupils to dilate
What occurs in the light reflex pathway on the afferent limb?
Light falls on retina
Impulses travel along optic nerve to optic chiasma to optic tract
Fibres don’t go to LGB, go to midbrain instead
Pupillary reflex fibres go to edinger-westphal nucleus in CN III nucleus
What occurs in the light reflex pathway on the efferent limb?
Preganglionic parasympathetic fibres from edinger-westphal nucleus
Pass through CN III into orbit
Parasympathetic fibres go to and synapse in ciliary ganglion
Postganglionic fibres go through short ciliary nerves to constrictor pupillae
Causes pupillary constriction of both sides
What can cause absent/abnormal pupillary reflex?
Diseases of the retina - detachment/degenerations/dystrophies
Diseases of the optic nerve - e.g. optic neuritis
Diseases of CN III
What is the clinical relevance in CN III palsy related to pupillary reflex?
In medical cause (e.g. diabetes), usually no damage to parasympathetic fibres
If CN III palsy present, pupillary reflex needs checked, if absent - potential cerebral artery aneurysm = EMERGENCY
What is Horner’s syndrome?
Anisocoria due to damage tot he sympathetic innervation to the pupil
