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69 Cards in this Set

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Resting primary gaze
Looking fwd, all of the eye muscles are balanced
What is the function of CN3
It is involved in pupillary light reflex, it also opens the eye lids, it does superior rectus, medial rectus, and inferior rectus. It basically controls 4 extraocular and 2 intraocular muscles and the eye lid
None
What does CN4 innervate
Superior oblique
What does CN6 innervate
Lateral rectus
Where are the cell bodies for CN3 located
They are located in the midbrain
Where are the cell bodies for CN4 located
Midbrain
Where are the cell bodies for Cn6 located
Pons
What are the primary eye movements
Intorsion and extorsion
What is Intorsion
Upper pole of the eye move in and this mediated by superior oblique
What is extorsion
Upper pole of the eye lid moves out and this is mediated inferior oblique
What muscle is used to move the eyes towards the nasal side
Medial rectus
What muscles of the eye are used to move the eyelid towards temporal side
Lateral rectus
What part of the body conjugates the eye movement
CNS
What areas in the brain are associated with the eye movements
Brainstem, cerebellum, and forebrain along with the basal ganglia. Forebrain has the frontal eye fields and if + the left frontal eye fields, both of the eyes go to the left
What happens if there is stroke in the frontal cortex
The patient will have eyes deviated to the lesioned side, away for the paralysis
Where are horizontal eye movements control centers
Pons, it is the center for the horizontal eye movements, i.e. it does the right and left
What is the role of the abducens nucleus
It is the center for the horizontal gaze and the reason it can do this is because it supplies innervations to the ipsilateral lateral rectus and contralateral media rectus
What is the connection between the occulomotor, trochlear, abducens, and vestibular nuclei
It the MLF, this is a runner between all of these cranial nerves
What is one of the first signs of MS
Demeyleination of MLF
What is PPRF
It is located near the abducens nucleus and it provides the abducens nucleus with output from higher cortical eye movt centers
When CN3 synapses on the medial rectus, what kind of receptor is there and what is the NT released
The receptor is nicotinic and the released NT is Ach and this → formation of EPP
What if there is lesion in the PPRF
Lesion here or abducens nucleus causes ipsilateral horizontal gaze palsy, this → problem in both eyes with directed gaze, i.e. If normal when you look right both eyes should move to the right. This is just like the reins on the horse, if you want the horse to go right, pull on the right reins
Lesion in left side PPRF
When look to the right, the eyes go to the right, but when look to the left, the eyes are stuck in a horizontal gaze
What CN is responsible for closing the eye lid
CN7
Who does the vertical and vergence
Midbrain
Where are the vertical eye movements initiated? What muscles are implicated? And what does a lesion result in?
They are initiated in the rostral midbrain reticular formation and pretectal areas. This areas controls the superior and the inferior rectus muscles, the dorsal region controls the upward gaze and when; lesioned (pineal tumor)→ to the inability to do upward gaze. The ventral areas does the downward gaze and once lesion leads to ↓ ability to look downwards
Where is vergence initiated, muscles?
Vergence is initiated in the midbrain reticular formation, this area controls the convergence medial recti muscles and divergence via lateral recti muscles, also the descending controls from the occipital and parietal cortex control eye movements for near and far vision
What is the role of forebrain centers in the controls of the eye movements
They send info from cerebral cortex to the brainstem centers and the superior colliculi. They control the frontal eye fields which + the PPRF on the contralateral side and + conjugate movements to the contralateral sides and these are saccades.
What happens if there is a lesion in the frontal eye field
Both eyes gaze towards the lesioned side
What is the role of praieto-occipito-temporal cortex (POT CORTEX) and in what direction
They do smooth pursuit eye movements in ipsi direction
None
What are the 2 principle eye movements
Ones that change the line of sight and ones that keep the retinal image steady
Medial and lateral recti
They control left and right along the z-axis
Superior and inferior recti control
Up and down along the axis
Superior and inferior oblique
rotate the eyes to keep the image steady
Why are the eye muscle movements the quickest
b/s they do not work against gravity and their mechanical load is always the same
What are the functions of the occulomotor system
They integrate sensory and the motor systems and they keep the fovea in the retina directed and fixed on the subject of interest
What is the function of the fovea
It has the ↑ visual acuity in the eye and occulomotor system keeps the image steady to about 5 degrees even though our visual field is about 200 degrees. The images are kept steady via micro-eye movt, and since the eyes are attached to the head, any little movement of the head has an effect on the image, so the eyes have to be sensitive enough to be able to detect the tiny cardiac pulsations
VOR
Keeps the images of seen world steady on the retina during brief head rotations
OPTOKINETIC
Hold images steady during sustained head rotations
SMOOTH PURSUIT
To hold a moving target on the retina and is controlled by the POT cortex
NYSTAGMUS THE QUICK PHASE
To direct the fovea towards the oncoming visual scene during self rotation and to reset the eyes during prolonged rotation
SACCADES
Bring images of interest back to the fovea
VERGENCE
Move eyes in the opposite direction so that images of a single object are placed on the both foveae
What are the orbital mechanics of the eye
Phasic (pulse) or Tonic (step)
What is absolutely necessary for the eyes to move
We must overcome both the viscous drag and the elastic recoil forces of the supporting orbital tissue
What is pulse of innervations
It is the burst or ↑ in neural activity to the eye to generate a powerful contraction of the eye muscles, this has to be strong enough to overcome the resistance associated with the eye movements. The signal is velocity command, with out this the eye moves pretty slow and the amplitude or velocity of the eye movements depends on the duration of the burst or the pulse of the action potentials, remember this is Phasic
What is the tonic innervations
These are steady and these set a new level of threshold to keep the eyes at the new eccentric palace. These movements help us keep the eyes at a steady place which is not the primary position
What is the overall effect of the appropriate occulomotor command signals
The eye will be able to move back and forth and will be held in a new position, all of the MN commands for the eye have both velocity and position
What are the characteristics/functions of the Saccadic system
This is the fastest, about 700 degrees/sec, ballistic, cannot change these once these are started, allow us to rapidly redirect our line of sight, used in reading, voluntary and involuntary changes in the fixation, quick, fast phase of vestibular and optokinetic nystagmus and the rapid eye movement in REM sleep. Tiny saccades prevent visual images from disappearing due to retinal adaptation
What are the mechanics of the saccadic eye movements
There is a delay of about 200 msec between the appearance of the target and the start of the eye movement. Typical saccadic movement accelerates rapidly and reaches it’s peak between 1/3rd and ½ of the way through the movement, the eye gently decelerates but comes to an abrupt stop and the brain suppresses the visual image during the saccade so that the image is not blurred, and we are unconscious of the eye movement
Smooth pursuit system
Generates the movements of the eyes that match the pace of the target of the eyes, with a saccadic movement the target would quickly slide of the retina but the smooth pursuit will keep the targets on the fovea. The system does this by slow drifts which move the fovea over the target in smooth flicks, which are small saccades and they return the fovea to the target and maintain the eye position with the target in perspective. Look at the graphs on page 65-72
What does the smooth pursuit look like in a normal patent
/\ /\ /\/\/\/\
What does the smooth pursuit look like in a person with cerebellum problems
‘’//’’’’\’’\//\ irregular looking and the disorder is usually ataxia
What is the visucal acuity difference b/t smooth and Saccade
Smooth= excellent
Is the target required
Smooth= yes, sac=no
What is the maximum velocity for smooth vs. saccade
Smooth=100, sac=700
None
What is velocity under voluntary control
Smooth= no, it depends on the target velocity, sac= no
Proper stimulus to cause displacement in smooth vs. saccade
Smooth= velocity, sac= displacement
None
Latency
Smooth= 0.13 sec, sac= 0.2 sec
What are the vergence movements
Align the fovea of each eye to the targets located at different distances from the observer. Only type of eye movement that allows the eyes to move in an opposite direction, these are discongugate eye movements, line of sight for each converges with near object of interest and diverges with the far object of interest
What is the triad of near reflex
Convergence of the eyes, lens accommodation w/c ↑ lens strength to bring close objects into focus and is mediated via PNS, and constriction of the pupil, which sharpens the image on the retina and ↑ the depth of the PNS
When are vergence eye movements induced
During binocular vision
What does the horizontal vergence vs. the vertical
Pons does horizontal and midbrain does the vertical
What 2 systems work synergistically to hold images stable on the retina
CN8 (vestibular) and CN2 (optokinetic)
What does the vestibular system generate
It generates the VOR
What does the VOR do
It promptly compensates for the natural head movements which are usually rapid and transient by generating an eye movement that is equally rapid but in the opposite direction of the head. This system is ineffective with steady rotation and since the compensatory eye movements cease after 3o sec (endolymph catches up). REMEMBER THAT THE EYES ALWAYS MOVE IN THE OPPOSITE DIRECTION OF THE HEAD, HEAD RIGHT EYES LEFT!(look at page 71)
What is the function of the optokinetic system
It is mediated via the CN2, used during sustained or slow head rotation, + of this reflex requires a moving stimulus
What is the optokinetic nystagmus composed of
It is made up of the pursuit eye movement to track the moving environment like being in a train and looking at the utility poles. Once started this system keeps going until the field of the vision stops, even if the stimulus stops this can keep it’s effect for a while and helps to nullify postrotatroy eye movements. It acts as a backup to the VOR, VOR by itself can only hold the image for about 30 sec and once VOR is done, the image begins to traverse the retina and this is the + for optokinetic system and this stabilizes the image on the retina (look at page 72)
What is the visucal acuity difference b/t smooth and Saccade
Smooth= excellent
saccade=poor