Lec 21 Eye Movements Flashcards
(44 cards)
What is the relationship between the pulling directions of extraocular eye muscles and the planes of semicircular canals?
same plane
What muscles are reponsible for horizontal eye movements?
- only medial and lateral rectus
What muscles are responsible for vertical eye movement?
SR, IR, SO, IO
elevation = SR and IO depression = IR and SO
What muscles control torsion when eye is abducted?
superior oblique = intorsion [top of eye toward nose]
inferior oblique = extorsion [top of eye away from nose]
What muscles control torsion when eye is adducted?
superior rectus controls intorsion [top of eye toward nose]
inferior rectus controls extorsion [top of eye away from nose]
Where are the oculomotor nuclei located?
in midbrain at level of superior colliculi
What does the oculomotor nerve innervate?
- medial, superior, inferior recti
- inferior oblique
- levator palpebrae
- caries parasympathetic from edinger-westphal nucleus to ciliary ganglion to innervate pupillary sphincter
What does the trochlear nerve innervate?
superior oblique
– nerve nuclei is contralateral to the eye it innervates
What does the abducens innervate?
lateral rectus
What are clinical signs when 3rd nerve function completely eliminated?
- ptosis [lid is closed]
- eye “down and out”
- pupil dilated [mydriasis]
- eye nonreactive to light
- loss of accomodation
- impaired elevation, depression, adduction [b/c weak medial rectus]
What is common cause of 3rd nerve palsy?
- aneurysm of posterior communicating artery
- uncal herniation
What is emergency sign of impending brain herniation?
- hutchinson pupil –> dilated non-reactive pupil caused by compression of 3rd nerve by herniation of temporal lobe uncus
Where are the paired trochlear nuclei located?
- close to ventromedial edge of periaqueductal gray in midbrain
- at level of inferior colliculi
What are signs of CN 4 dysfunction?
- elevation of affected eye [hypertropia]
- vertical diplopia [double vision]
- may present with head tilt in direction of the affected eye
what is path of oculomotor nerve?
- exits ventral in midbrain, passes between PCA/SCA through cavernous sinus to superior orbital fissure
what is path of CN4?
exits dorsally from midbrain and decussates
then through cavernous sinus to superior orbital fissure
What is the origin of CN4 dysfunction?
- head trauma
- congenital defect
Where is abducens nuclei located?
lower pons / floor of 4th ventricle at facial genu/colliculus
What is path of abducens nerve?
exits nucleus in pons, passes under gruber’s ligament
through cavernous sinus to superior orbital fissure
What are signs of abducens nerve dysfunction?
- medially directed eye [can’t adduct] on ipsilateral side
- deviation of eye toward one another [esotropia]
Where is lesion likely to be if oculomotor, trochlear, and abducens all affected in one eye? how can you determine?
- likely either orbital apex or cavernous sinus
if orbital apex –> optic nerve also affected so loss of vision
if cavernous –> no vision loss
What is the medial longitudinal fasiculus? function?
MLF = bilateral fiber tract along cerebral aqueduct/ ventricle 4
- used by interneurons of abducens 6 nucleus to synapse on contralateral medial rectus subnucleus of CN 3
- facilitates conjugate horizontal eye movements [can coordinate simultaneous contraction of ipsilateral LR and contralateral MR]
What two types of neurons are in the abducens nucleus?
- lower motor neurons
- internuclear neurons
What nerves does the part of MLF rostral to abducens nucleus interconnect?
- vestibular nuclei
- nuclei of 3, 4, 6
