Cranial Nerves _ Oculomotor Flashcards
For the visual system to work efficiently, both eyes must focus and remain focused on:
an object so the information can reach cortex in a form that can result in vision.
While we can detect objects over a large range extending into the periphery, we “see” objects only when:
they are focused on the fovea.
The oculomotor system, controlling the movement of our eyes, is designed to (2 functions):
1) bring targets onto the fovea, and 2) keep them there.
Historically, five movement systems have been identified that put the fovea on a target (both eyes in a conjugate manner; foveation) and keep it there. They are as follows:
- movements that stabilize the eye when the head moves
2. movements that keep the fovea on a visual target
Movements that stabilize the eye when the head moves are classified as ___________________ and ____________________.
• vestibulo-ocular
and
• optokinetic
Movements that keep the fovea on a visual target are classified as ___________________, ___________________ and ____________________.
- saccade
- smooth pursuit
- vergence
vestibulo-ocular =
vestibular input holds images stable on retina during head and body movement; gaze stabilization
optokinetic =
visual input holds images stable on retina during sustained or slow head rotation
saccade =
brings new objects of interest onto fovea
smooth pursuit =
holds image of a moving target on the fovea
vergence =
adjusts eyes for viewing different distances in depth
In an oculomotor system that is functioning normally, the two eyes are:
“locked” together.
This allows both eyes to be focused on an object.
If the system becomes “unlocked” and the eyes focus on different targets (retinal disparity), what occurs?
diplopia or double vision occurs.
While the first four systems allow for the conjugate movements of the eyes for foveation, the vergence system allows for:
convergence or divergence (disconjugate movements)
What is diplopia?
the subjective complaint of seeing 2 images instead of one and is often referred to as double-vision.
The Saccade System is used to quickly:
reposition the eyes (fovea) to focus on an image that has suddenly been moved from the fovea.
Saccades can be ________________ or _________________.
horizontal or vertical
with the horizontal being the best understood from a neuronal pathway point of view.
What is the rapid eye movement required to bring the image back into focus?
saccade
Reading this card is done by a series of ________________ saccadic eye movements.
conjugate
Saccadic eye movements can be elicited by what types of inputs?
Visual input, auditory stimuli, memories of locations, or verbal commands.
Both eyes move in conjugate manner, in terms of ______________, _______________ and _____________ for reestablishment of the image on the fovea
velocity, amplitude and direction for reestablishment of the image on the fovea
This movement (reestablishment of image on fovea) is similar to the quick or saccade phase of _________________________.
vestibular nystagmus
This conjugate system is directed through a horizontal gaze center located in the ________________________________________,
pontine reticular formation (paramedian pontine reticular formation; PPRF)
Where is the PPRF located?
adjacent to the abducens nucleus.
The “upper motor neuron control” is a complicated system of interneurons, that involves a part of the middle frontal gyrus termed the _________________________ and the Superior Colliculus.
Frontal Eye Fields (FEF; area 8)
This cortical region is represented on both _____________________ and contains specific regions termed _______________ center, _______________center and a _______________ center.
hemispheres
horizontal gaze center, vertical gaze center and a vergence center
** These are separate and distinct regions within area 8.
Do vestibulo-ocular and Optokinetic reflexes work together?
Yes
As your head turns, your eyes are fixed on an object. Your eyes remain fixed and focused on that position by moving at the same speed as your head, but in the opposite direction. This is driven by the:
bilateral input of the vestibular system. [See diagram 15-8 in your text]
When the eyes reach a point in the periphery where they can no longer focus on that object, due to the image now being _________________________________ they reset to a new __________________________.
directed to the peripheral retina,
fixation point
This rapid movement is a saccade and is rapid enough that visual input is _______________________________.
The result is termed a ROTATORY NYSTAGMUS.
momentarily impaired until the foveas fixate on the next point.
This (rotatory nystagmus) has two components:
- the slow movement of fixation and
2. the rapid movement of resetting.
This vestibulo-ocular reflex is ______________ driven, due to the directional flow of endolymph _______________ the direction your head is turning.
vestibular
opposite
If the head continues to rotate, as on a spinning chair, the ________________ eventually “catches up” or stabilizes.
Then, the same pattern of following and ________________________ continues to take place as long as your head continues to turn.
endolymph
saccadic reset reaction
This continuation of following and resetting of the focal point is now driven by the _____________________ (the vestibular input is balanced).
optokinetic system
The optokinetic system requires input from the _________________ and _________________.
visual cortex and the superior colliculus.
Once the rotation is stopped, the eyes will react in the _______________ direction.
opposite
The slow following eye movement will be in the direction of ______________ and the saccade in the ________________ direction of prior rotation.
PRIOR ROTATION
OPPOSITE
= postrotatory nystagmus
What is postrotatory nystagmus ?
- Reflexive movements of the eyes after a quick rotational movement (e.g., spinning) observed to determine vestibular dysfunction.
- Involuntary oscillation of the eyes as a result of being rotated after stimulation of the vestibular system by spinning activities.
Is postrotatory nystagmus vestibular driven?
yes
The rotation of endolymph in the horizontal ______________ canals and the effects they have on the activity of the hair cells of the _______________ will be discussed later.
semicircular
cupula
What is rotatory nystagmus?
involuntary rotation of the eyes about the visual axis.
Smooth Pursuit requires an image to be moving across the:
field of vision.
Smooth pursuit movements are not under _______________________ once fixation on the image has been established.
volitional control
The PPRF is involved, but the “upper motor neuron” control comes from visual signals from ____________________, channeled through an area in the _____________________, coupled with _____________________.
primary visual cortex
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 ___________________________________________or ____________________________________________.
reflexive pathways such as the vestibulo-ocular reflex (quick phase of nystagmus)
OR
voluntarily as in the saccades initiated from the appropriate center of Frontal Eye Fields.
All of the systems for conjugate eye movements are influenced by __________________ through feedback information to the vestibular nuclei and then to the horizontal and/or vertical gaze centers.
cerebellum
For instance, the ___________________ responds to differences in head versus eye movements and “adjusts” the __________________ of the vestibular nuclei to correct the velocity of the eye movements to match the head movements.
flocculus
interneurons
The Vergence system is controlled through the ________________________ at the midbrain level.
reticular formation
The _____________________ movements of the eyes are necessary for the foveation of an image as it moves _________________________.
disconjugate
toward or away from you.
For ___________________, an activation of both _____________________ muscles must override the lateral rectus muscle tone to bring the eyes together.
convergence
medial rectus
To overcome blurring of the image as it comes closer, this mechanism is coupled with _____________________________________________________________ for changing of focal distances.
pupillary constriction and accommodation (rounding of the lens)
Cortical control of this system is located in the visual cortical areas and the vergence gaze center, an area ______________ to the horizontal gaze center. Deficits associated with horizontal or vertical gaze centers do not impair ____________________________.
rostral
convergence or accommodation
SUPERIOR COLLICULUS -
nucleus located rostrally in the midbrain tectum (the region dorsal to the cerebral aqueduct of Sylvius).
(Superior Colliculus) receives “upper motor neuron” fibers from the _____________ cortex (frontal eye fields - Brodmann’s area 8, ______________ lobe and caudal _____________ lobe).
ipsilateral
OCCIPITAL lobe and caudal TEMPORAL lobe.
“Tectobulbar” connections to the nuclei of the cranial nerves innervating the _________________ eye muscles are a part of the pathway for ___________________________movements of the eyes, and are analogous to ___________________________ [Area 8 (Frontal Eye Fields) projects to superior colliculus].
extraocular
voluntary and involuntary
“upper motor neurons,”
bulbar refers to:
brainstem
Receives (tectobulbar) direct retinal projections from the optic tract via the ________________ of the superior colliculus.
brachium
Descending efferent information is directed to the spinal cord and cranial nerve nuclei. The tectospinal tract crosses in the ______________ and descends to cervical spinal cord levels.
midbrain
Tectospinal tract is important in the reflex _______________________________ in response to both visual and auditory cues.
turning of the head and neck
PRETECTAL AREA -
composed of a number nuclei and located rostral to the superior colliculus.
(Pretectal area) receives projections from the:
cortex, retina and superior colliculus.
Efferents (from pretectal area) are directed to cranial nerve motor nuclei and the preganglionic parasympathetic neurons associated with _________ for reflex control of the ________________ and ________________.
CN III
pupil and lens
ALL OF THE CRANIAL NERVES INVOLVED WITH MOVEMENT OF THE EYE, VOLUNTARY OR INVOLUNTARY, ARE INTERCONNECTED THROUGH AXONS TRAVELING IN THE:
MEDIAL LONGITUDINAL FASCICULUS (MLF).
Abducens Nerve (CN VI) -
lower motor neurons innervating lateral rectus muscle.
Abducens nerve exit the brainstem laterally adjacent to the pyramids at the:
pontomedullary junction.
The abducens functions in ______________ of the eyeball.
abduction
Tectobulbar fibers terminate in a __________________________, adjacent to the abducens nucleus = __________________________________________. This nucleus then projects to the abducens nucleus.
reticular formation nucleus
… the PARAMEDIAN PONTINE RETICULAR FORMATION (PPRF; horizontal gaze center).
HORIZONTAL CONJUGATE GAZE [template] - internuclear neurons from the abducens nucleus (different than interneurons of PPRF) project to the _____________________________ for inhibition of _______________ lower motor neurons innervating medial rectus.
ipsilateral oculomotor complex
ipsilateral
Internuclear neurons from PPRF project to the _____________________ oculomotor complex for activation of ___________________ medial rectus. These axons run in the ____________________________________.
contralateral
contralateral
contralateral MLF
STRABISMUS –
a visible turn of one eye that may be constant. Also termed tropia (esotropia or exotropia).
Phoria refers to the point of:
vergence of the eyes
Esophoria is where the eyes are postured in __________ of the point of focus
front
Exophoria is where the eyes are postured in_____________ of the point of focus.
back
Myopia = or
(near sighted)
** different than exopheria
hyperopia=
far sighted
Myopia and hyperopia are for where the image is focused with respect to the ______________, not where the point of vergence is with respect to the _______________________________.
retina
object the patient is viewing
ESOTROPIA =
a lesion of the abducens nerve fibers results in unopposed adduction of the ipsilateral eye.
A lesion of the abducens nucleus (includes PPRF) results in:
paralysis of horizontal gaze ipsilateral to the lesion (can’t look to the side of the lesion).
Internuclear ophthalmoplegia (MLF damaged in pons) - actions of the abducens and oculomotor nerves are:
uncoupled
Excursion of the abducting eye is full, but adduction of the other eye is __________. This is the side the damage to the MLF is ___________. Abducting eye will also exhibit __________________.
impaired
located
pendular nystagmus
Pendular nystagmus is thought to be due to loss of
inhibitory fibers in MLF.
Trochlear Nerve (CN IV) -
lower motor neurons innervating the contralateral superior oblique muscle.
The axons of this nerve (CN IV) course dorsally around the:
periaqueductal grey and decussate.
The nerve (CN IV) then courses around the brainstem to occupy a position ___________ to the oculomotor nerve between the ________________________________
lateral
superior cerebellar and posterior cerebral arteries.
CN IV functions in _______________ and _______________ of the eyeball.
rotation and
depression
Lesion of the trochlear nerve (RARE) is marked by an inability to:
look down and thus problems walking down stairs.
Vertical gaze is also coordinated through a vertical gaze center (Interstitial nucleus of ____________; located near ____________ nucleus)
Cajal
trochlear
Oculomotor Nerve (CN III) -
lower motor neurons for the remainder of the extraocular eye muscles and levator palpebrae superioris, all ipsilateral, (except to superior rectus).
CN III also contains:
preganglionic parasympathetic fibers to the ciliary ganglia.
The oculomotor nuclear complex is divided into individual cell groups responsible for the innervation of each _____________.
muscle
The preganglionic parasympathetic cell bodies lie in an ________________ nucleus, the ________________________ nucleus.
adjacent
Edinger Westphal
All of the fibers from these nuclei traverse the ______________ near the ________________ and cross the _________________ to exit in the _________________ fossa. The nerve can be seen exiting between the superior cerebellar and posterior cerebral arteries.
tegmentum
red nucleus
cerebral peduncles
interpeduncular
EXOTROPIA -
a lesion of the oculomotor nerve.
Oculomotor palsy, causes:
paralysis of all extraocular eye muscles except LR and SO, and results in unopposed abduction of the ipsilateral eye.
Drooping of the eyelid is also noted (in oculomotor palsy) due to the involvement of __________________________________.
levator palpebrae superioris
Loss of parasympathetic innervation of the ciliary ganglia results in:
dilation (mydriasis) of the pupil.
Horizontal conjugate gaze, volitional or pursuit:
- paralysis of volitional horizontal conjugate gaze
- internuclear ophthalmoplegia
Fixation and convergence -
Accommodation reflex.
***REVIEW the pathway for this reflex.
Pupillary light reflex (this reflex and testing for its integrity) requires an intact
optic nerve and tract.
**See figure at end of handout.
Argyll-Robertson pupil: Seen in tertiary syphilis. The pupil is ________________________________________ Will
_______________ in accommodation associated with convergence.
small in dim light and non-reactive to light.
constrict
2 Alternating hemiplegias =
- Abducens or middle alternating hemiplegia
2. Oculomotor or superior alternating hemiplegia
Horner’s Syndrome -
lesion of sympathetic nervous system pathway; descending influence from the hypothalamus directed to preganglionic sympathetic neurons in the spinal cord, or any of the peripheral pathways carrying sympathetic fibers.
In Horner’s syndrome, if that involvement is to sympathetics directed to the head (ascending sympathetic chain, superior cervical ganglion), the clinical manifestation in the face is as follows (4):
- ptosis
- miosis
- dry skin
- flushed skin
ptosis =
due to loss of sympathetic innervation to superior tarsal muscle of the eyelid and its control by levator palpebrae superioris
miosis =
(pupil constricted) - loss of dilator control; unopposed constrictor tone (parasympathetic).
dry skin =
(absence of sweating) - loss of sympathetic control of sweat glands
flushed skin =
lack of constriction of capillary field
