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
What is a likely cause of unilateral CN III eye muscle paresis without unilateral enlarged pupil?
Diabetes mellitus (small vessel dz) --> the superficial position of parasympathetic fibers along blood vessels makes them less prone to the ischemic dz causes by diabetes, so the constrictors are usually not involved
What is the accommodation reflex?
Convergence of the eyes along with parasympathetic mediated constriction of the pupil and thickening of the lens to allow for near vision
Subsequent activation by cortical areas (including supraocularmotor area) of what 2 nuclei is required to produce the coordinated actions in the accommodation reflex?
Edinger-Westphal nucleus --> pupil constriction and lens thickening
Ventral nucleus of CN III (bilaterally)--> movement do medial rectus muscles
What is the clinical consequence of failure of conjugate lateral eye movement?
Diplopia--> eyes no longer "yoked" so not looking at some spot
What fibers are responsible for the ability to have conjugate lateral eye movement? (Looking left causes both eyes to move at same time)
The medial longitudinal fasciculus (MLF)
What structures does the MLF connect?
Connects the abducens nucleus to the contralateral ventral nucleus of CN --> allows for simultaneous contraction of lateral rectus (abducens nucleus) and contralateral medial rectus (ventral nucleus of III)
What is the function of the paramedian pontine reticular formation (PPRF)?
Allows for simultaneous actions of the lateral rectus (on ipsilateral side to the PPRF) and contralateral medial rectus (via contralateral ventral nucleus)--> phasic firing
What will a lesion of the right MLF cause?
When patient is asked to look to the left, the left eye will a duct, but the right will not adduct (right MLF is the one coming from the left abducens nuclei and going to the right ventral nucleus of III--> crosses midline immediately, so never really on the left side)
How will the accommodation reflex be affected by a lesion of the MLF?
It won't --> normal accommodation reflex would be seen
What gaze deficit would be seen with a right abducens n lesion?
In looking right, the right eye will not adduct; both eyes normal in left gaze
*affected side with lesion will lose ability to adduct
What gaze deficits would be seen with a right abducens nucleus lesion?
Neither eye would move in a rightward gaze; left gaze normal--> failure of right lateral rectus and also no input through the MLF to left medial rectus (right lateral gaze palsy)
* failure of both eyes to go toward side of lesion
What gaze abnormality would be seen in a right PPRF lesion?
Failure of either eye to go towards the right; left gaze normal
*same issue as an abducens nucleus lesion
What gaze abnormalities would be seen in a left MLF lesion (left intranuclear opthalmoplegia)?
In right gaze, right eye will abduct with nystagmus, but left eye will not adduct; leftward gaze normal
*seen frequently with MS
What gaze abnormalities would be expected in a left MLF lesion with Left abducens nucleus lesion (1 1/2 syndrome)?
On rightward gaze, nystagmus in right eye (w/ abduction) and left eye doesn't move
On leftward gaze, there is no movement of either eye (stay in midline)
What is the vestibulo-ocular reflex? It is used to test structural integrity of what two structures?
Turning head to one side will cause eyes to go to that side in the new direction of gaze
* tests integrity of midbrain to pons; in comatose patients, the eyes will remain fixed in one location as head is moved back and forth (oculocephalic or Dolls eyes maneuver)
Which nucleus is responsible for the vestibulo-ocular reflex? How does it mediate its action?
Medial vestibular nucleus --> sends projections to the contralateral PPRF and thus activate the abducens nucleus and ventral nucleus of III to turn eyes in direction head turned
* rotation of head to right= activation of lateral semicircular canal->right medial vestibular nucleus-> contralateral (left) PPRF-> left abducens nucleus and right ventral nucleus of III
What are saccades?
Fast conjugate ("yoked") eye movements
What cortical structure controls saccadic eye movements?
Frontal eye field
* vestibulo-ocular reflex is an example of a saccadic reflex
From the frontal eye field, where to fibers in the saccadic pathway travel before going to the PPRF? It travels to the PPRF on which side relative to the frontal eye field activated?
Travels to ipsilateral superior colliculus--> contralateral PPRF
The ____ frontal eye field causes the eyes to turn to the right
Left (will activate the right PPRF--> right lateral rectus and left medial rectus= look to right)
* the left hemisphere (which contains the left eye field) controls right hand, so if catching a ball with the right hand, you want eyes looking right
Slow pursuit eye movements are under control of what cortical region?
*slow pursuit movement are slow conjugate (yoked) eye movements
The POT area involved in the slow pursuit eye movements directs gaze to which side (relative to the POT on the side of the brain activated)?
To the ipsilateral side
Signals are sent from the POM to the _______ cerebellum and vestibular nuclei in slow pursuit eye movements.
In frontal cortex lesion (above the brainstem) which direction would the eyes point relative to lesion?
Would point away from the side paralyzed
* in a left frontal lobe lesion, there is right hemiparesis and a loss of input to right PPRF, so left PPRF takes over--> eyes to the left (away from paralyzed side, which is the right)