Flashcards in Eye Movement - CN III, IV, VI (14) Deck (54)
CN III and IV lie in the midbrain just ventral to which two structures, respectively?
Superior and inferior colliculi
CN VI nucleus lies in the caudal 1/2 of the _____.
Dorsal nucleus of CN III operates which eye muscle?
Intermediate nucleus of CN III operates which eye muscle?
Medial nucleus of CN III operates which eye muscle?
Ventral nucleus of CN III operates which eye muscle?
Trochlear nucleus of CN IV which operates eye muscle?
Central caudal nucleus of CN III operates which eye muscle?
Levator palpeprae superior
Which nucleus operates the lateral rectus?
Abducens nucleus--> serves CN VI
What structure in the floor of the 4th ventricle does the nucleus of CN VI (abducens) lie just below?
Which CN III nerve is served by the nucleus on the contralateral side to the eye controlled?
Medial nucleus ---> so superior rectus
Lateralized lesions of what 2 things can produce unilateral eye movement and pupillary abnormalities ?
2. CN III after it leaves the brainstem
What CN is the only one that exits the brainstem dorsally?
CN IV - Trochlear, which serves the superior oblique
Other than superior rectus, what other eye muscle is innervated by the CN on the contralateral side?
Superior oblique --> CN IV, Trochlear
*contralateral = Trochlear nucleus and medial nucleus of CN III
Which two arteries does CN III pass between after leaving the brainstem?
Superior cerebellar and posterior cerebral arteries
* passes under the internal carotid also---> fork these reasons!I to s susceptible to compression/injury from aneurysms
What 5 CN/ CN parts pass through the cavernous sinus and are thus subject to injury due to injury or hemorrhage in this area?
1. CN III
2. CN IV
3. CN VI
4. V1 (opthalmic)
5. V2 (maxillary)
Which muscle, innervated by which CN is responsible for voluntary elevation of eyelid?
Levator palpeprae superioris --> CN III
What muscle provides autonomic elevation of eyelid? What division innervates?
Tarsal muscle --> sympathetic fibers
How do you test the superior or inferior rectus muscles in isolation?
Have patient look laterally, then up to test superior rectus or down for inferior rectus
How do you test the superior and inferior obliques in isolation? (Which direction for which muscle?)
Have the patient look medially, then look down to test superior oblique and up to test inferior oblique
What is a quick and dirty way to tell if a CN III lesion is complete or partial?
Since it innervates the levator palpeprae, complete lesions will result in the eye being closed fully, while partial lesions will cause only partial closure (zeal so weakness or paresis of movement)
CN III innervates all eye muscle except which two? What innervates these?
Lateral rectus muscles--> CN VI (Abducens)
Superior oblique--> CN IV (Trochlear)
Where do primary neurons of origin of the sympathetic NS originate in the brain?
In the hypothalamus
Via which nerve do sympathetic fibers reach the superior tarsal muscles?
Via which nerves do sympathetic fibers reach the dilator muscles of the pupils?
Long and short ciliary nerves
Afferent signals due to light being shown in the eye travel with the optic nerve to what nuclei?
Left and right pretectal nuclei (in midbrain just under the superior colliculi)
How do efferent signals due to light shown into the eye get back to the eye to cause pupil constriction in the light reflex? (What nucleus and what CN)
Via the Edinger-Westphal nucleus to fibers of CN III to constrictor muscles (through ciliary ganglia and short ciliary n.)
Why does the consensual (indirect) light reflex response exist? (Why do both pupils constrict due to light being shown into only one)
Because the Edinger-Westphal nucleus sends out bilateral axons, so stimulation of it via the light reflex will cause constriction of pupils bilaterally
* also there is only one central Edinger-Westphal nucleus, compared to most which have on on either side
Why is acute onset of unilateral paresis of CN III muscles and unilateral enlarged pupil a neurologic emergency?
Are often due to compression of CN III by an aneurysm, which has a 30-40% mortality rate