Cranial Nerves - Oculomotor Flashcards
The oculomotor system (controlling the movement of our eyes) is designed to do what two things?
- bring targets onto the fovea
- and to keep them there
What five movement systems have been identified to put the fovea on a target and keep it there?
- vestibulo-ocular
- optokinetic
- saccade
- smooth pursuit
- vergence
What 2 movement systems stabilize the eye when the head moves?
- vestibulo-ocular
- optokinetic
What 2 movement systems keep the fovea on a visual target?
- saccade
- smooth pursuit
- vergence
What movement system provides vestibular input that holds images stable on the retina during head and body movement (gaze stabilization)?
vestibulo-ocular
What movement system brings new objects of interest onto the fovea?
saccade
What movement system holds the image of a moving target on the fovea?
smooth pursuit
What movement system provides visual input that holds images stable on the retina during sustained or slow head rotation?
optokinetic
What movement system adjusts the eyes for viewing different distances in depth?
vergence
In an oculomotor system that is functioning normally, the two eyes do what? (locked or unlocked?)
the two eyes are “locked” together (both eyes focus on an object)
What is the result of the eyes being unlocked?
the eyes focus on different targets (retinal disparity), diplopia or double vision occurs
What movement systems allow for conjugate movements of the eyes for foveation?
- vestibulo-ocular
- optokinetic
- saccade
- smooth pursuit
What movement system allows for convergence or divergence (disconjugate movements)?
vergence system
What movement system is used to quickly reposition the eyes (fovea) to focus on an image that has suddenly been moved from the fovea?
Saccade system
What is the term for rapid eye movement required to bring the image back into focus?
saccade
The saccade system is directed through what? located where?
directed through a horizontal gaze center located in the pontine reticular formation (paramedian pontine reticular formation; PPRF) adjacent to the abducens nucleus
The “upper motor neuron control” of the saccade system is a complicated system of interneurons that involves what areas/structures of the brain?
- part of the middle frontal gyrus termed the Frontal Eye Field (FEF; area 8)
- the Superior Colliculus
What are 3 separate and distinct regions within area 8 (Frontal Eye Field)?
- horizontal gaze center
- vertical gaze center
- vergence center
What 2 movement systems/reflexes work together to keep your eyes fixed on an object as your head turns?
vestibulo-ocular and optokinetic reflexes
Your eyes remain fixed and focused on an object by moving at the same speed as your head, but in the opposite direction. This is driven by bilateral input of what system?
vestibular system
When the eyes reach a point in the periphery where they can no longer focus on that object, due tot he image now being directed to the peripheral retina, they reset to a new fixation point. This rapid movement is known as what?
saccade (the movement is rapid enough that visual input is momentarily impaired until the foveas fixate on the next point)
The result of the visual input being momentarily impaired until the foveas fixate on the next point is termed what?
rotatory nystagmus
What are the two components of rotatory nystagmus?
- the slow movement of fixation
- the rapid movement of resetting
This vestibulo-ocular reflex (eyes remain fixed on an object when head turns and refixating) is driven by what system? due to what?
driven by the vestibular system, due to the directional flow of endolymph opposite the direction your head is turning
If the head continues to rotate, what happens to the endolymph?
the endolymph eventually “catches up” or stabilizes
The same pattern of following and saccadic reset reaction continues to take place as long as your head continues to turn. This continuation of following and resetting of the focal point is now driven by what system?
optokinetic system (the vestibular input is balanced)
the optokinetic system requires input from what area/structures of the brain?
the visual cortex and the superior colliculus
Once the rotation of the head stops, the eyes will react in what direction?
the opposite direction of the rotation
The slow following eye movement (after head stops rotating) will be in what direction? The saccade will be in what direction?
the slow following eye movement will be in the direction of prior rotation and the saccade in the opposite direction of prior rotation
The slow following eye movement will be in the direction of prior rotation and the saccade in the opposite direction of prior rotation. This is known as what?
postrotatory nystagmus
Postrotatory nystagmus is driven by what system?
vestibular system
What movement system requires an image to be moving across the field of vision?
Smooth Pursuit
Are smooth pursuit movements under volitional control once fixation on the image has been established?
NO
Is the PPRF involved smooth pursuit movements?
YES
The “upper motor neuron control” of smooth pursuit movements comes from what? channeled through what? coupled with what?
comes from visual signals from primary visual cortex, channeled through an area in the caudal temporal gyrus, coupled with superior colliculus
The PPRF has a number of different types of neurons that control saccade and smooth pursuit conjugate eye movements. These can be activated through what?
reflexive pathways such as the vestibulo-ocular reflex or voluntarily as in the saccades initiated from the appropriate center of FEF
All the systems of conjugate eye movements are influenced by what?
influenced by the cerebellum through feedback information to the vestibular nuclei and then to the horizontal and/or vertical gaze centers
The vergence system is controlled through what?
the reticular formation at the midbrain level
The disconjugate movements of the eyes are necessary for what?
necessary for the foveation of an image as it moves toward or away from you
For convergence, what muscles must be activated and what is their role?
both medial rectus muscles must override the lateral rectus muscle tone to bring the eyes together
To overcome blurring of the image as it comes closer, this mechanism is coupled with what 2 actions in order to allow for changing of focal distances?
- pupillary constriction
- accommodation
Cortical control of the vergence system is located where?
located in the visual cortical areas and the vergence gaze center, an area rostral to the horizontal gaze center
Do deficits associated with horizontal or vertical gaze centers impair convergence or accommodation?
NO
The nucleus of what brain structure is located rostrally in the midbrain tectum (the region dorsal to the cerebral aqueduct of Sylvius)?
superior colliculus
The superior colliculus receives UMN fibers from where?
ipsilateral cortex (FEF - Brodmann’s area 8, occipital lobe and caudal temporal lobe)
“Tectobulbar” connections to the nuclei of the cranial nerves innervating the extraocular eye muscles are a part of the pathway for what?
voluntary and involuntary movements of the eyes
Those same tectobulbar connections are analagous to what?
upper motor neurons (FEF projects to the superior colliculus)
The superior colliculus receives direct retinal projections fro the optic tract via what?
the brachium of the superior colliculus
Descending efferent information from the superior colliculus if directed where?
to the spinal card and cranial nerve nuclei
The tectospinal tract crosses where and descends to what?
crosses in the midbrain and descends to cervical spinal cord levels
What tract is important in the relfex turning of the head and neck in response to both visual and auditory cues?
tectospinal tract
What area is composed of a number of nuclei and located rostral to the superior colliculus?
Pretectal area
The pretectal area receives projections from where?
receives projections from the cortex, retina, and superior colliculus
Efferents of the pretectal area are directed to what?
cranial nerve motor nuclei and the preganglionic parasympathetic neurons associated with CN III for reflex control of the pupil and lens
All of the cranial nerves involved with movement of the eye, voluntary or involuntary, are interconnected through axons traveling in what?
the Medial Longitudinal Fasciculus (MLF)
What do the LMNs of the abducens nerve (VI) innervated?
ipsilateral lateral rectus muscle
The axons of the LMNs of CN VI exit the brainstem laterally adjacent to the pyramids at what point?
at the pontomedullary junction
Function of LMNs of CN VI?
abduction of the eyeball
Tectobulbar fibers of the abducens nerve terminate where?
Paramedian pontine reticular formation (PPRF; horizontal gaze center)
PPRF then projects to what nucleus?
Abducens nucleus
Internuclear neurons from the abducens nucleus project where? to do what?
project to the ipsilateral oculomotor complex for inhibition of ipsilateral LMNs innervating medial rectus
Internuclear neurons from PPRF project where? to do what?
project to the contralateral oculomotor complex for activation of contralateral medial rectus
Axons projecting from the PPRF run through what?
run in the contralateral MLF
What is the term for a visible turn of one eye that may be constant?
stratbismus (aka tropia)
What term refers to the point of vergence of the eyes?
phoria
What term refers to where the eyes are postured in front of the point of focus?
esophoria
What term refers to where the eyes are postured in back of the point of focus?
exophoria
What is the term for near sighted?
myopia
What is the term for far sighted?
hyperopia
What two terms are for where the image is focused with respect to the retina, not where the point of vergence is with respect to the object the patient is viewing?
myopia and hyperopia
A lesion of the abducens nerve fibers results in what?
unopposed adduction of the ipsilateral eye
A lesion of the abducens nucleus (includes PPRF) results in what?
paralysis of horizontal gaze ipsilateral to the lesion (cannot look to the side of the lesion)
What results from MLF damaged in the pons?
- internuclear ophthalmoplegia - actions of the abducens and oculomotor nerves are uncoupled
- excursion of the abducting eye is full, but adduction of the other eye is impaired (this is the side the damage to the MLF is located)
- abducting eye will also exhibit pendular nystagmus
What causes the abducting eye to exhibit pendular nystagmus?
due to loss of inhibitory fibers in MLF
LMNs of the trochlear nerve (CN IV) innervate what?
the contralateral superior oblique muscle
The axons of the trochlear nerve course dorsally around what before decussating (crossing)?
the periaqueductal grey
What cranial nerve is involved in horizontal conjugate gaze?
abducens nerve (CN VI)
After decussation, the trochlear nerve then courses around the brainstem to occupy a position lateral to what nerve and between what 2 arteries?
lateral to the oculomotor nerve between the superior cerebellar and posterior cerebral arteries
LMNs of trochlear nerve function?
rotation and depression of the eyeball
A lesion of the trochlear nerve is marked by what?
an inability to look down and thus problems walking down stairs
Vertical gaze is coordinated by what center? what is the nucleus and where is it located?
vertical gaze center; interstitial nucleus of Cajal located near trochlear nucleus
LMNs of oculomotor nerve (CN III) innervate what muscles? ipsilateral or contralateral?
the remainder of the extraocular eye muscles and levator palpebrae superioris, all ipsilateral, (except to superior rectus)
The oculomotor nerve also contains preganglionic parasympathetic fibers to what?
the ciliary ganglia
What nucleus do the preganglionic parasympathetic cell bodies lie in?
Edinger-Westphal nucleus
All the fibers from the edinger-westphal nucleus travel what? and cross where? to exit where?
traverse the tegmentum near the red nucleus and cross the cerebral peduncles to exit in the interpeduncular fossa
The oculomotor nerve is seen exiting between what 2 arteries?
the superior cerebellar and posterior cerebral arteries
Exotropia is the result of a lesion to what cranial nerve?
oculomotor nerve
A lesion of the oculomotor nerve causes what pathology?
Oculomotor palsy
Symptoms of oculomotor palsy?
paralysis of all extraocular eye muscles except LR and SO and results in unopposed abduction of the ipsilateral eye
Because of the involvement of levator palpebrae superioris, oculomotor palsy results in what additional symptom?
drooping of the eyelid
Loss of parasympathetic innervation of the ciliary ganglia results in what?
dilation (mydriasis) of the pupil
What reflex is involved with fixation and convergence of the eye?
accommodation reflex
What reflex requires an intact optic nerve and tract?
pupillary light reflex
What is the name for the pupil that is small in dim light and non-reactive to light? It will also constrict in accommodation associated with convergence.
Argyll-Robertson pupil (seen in tertiary syphilis)
What are the 2 types of alternating hemiplegia?
- abducens or middle alternating hemiplegia
- oculomotor or superior alternating hemiplegia
What pathology results from a lesion of sympathetic nervous system pathway?
Horner’s Syndrome
What results from a loss of sympathetic innervation to superior tarsal muscle of the eyelid and its control by levator palpebrae superioris?
ptosis (drooping eyelid)
What results from a loss of dilator control; unopposed constrictor tone (parasympathetic)?
miosis (pupil constricted)
What results from a loss of sympathetic control of sweat glands?
dry skin (absence of sweating)
What results from a lack of constriction of capillary field?
flushed skin
