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89 Cards in this Set

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What is the purpose of eye movements?
Foveation
What is the fovea?
The center of the macula
What is the fovea used for?
-Fixating on objects
-High acuity vision
6 functional classes of eye movements:
1. Smooth pursuit
2. Saccades
3. Vestibular
4. Vergence
5. Optokinetic
6. Fixation
What is Smooth pursuit?
Eye movement that holds the image of a moving target steady on the fovea
What are Saccades?
Eye movements that bring objects of interest in the peripheral visual field onto the fovea.
What is Vestibular eye movement?
Eye movements that maintain foveation during brief head rotations and translations
What is Vergence?
When the eyes move in opposite directions to maintain foveation as objects approach or recede.
What is optokinetic eye movement?
Eye movement that stabilizes the image of the surrounding visual scene during sustained head rotations.
What does optokinetic eye movement take over for?
The vestibular eye movements that become insufficient to maintain foveation during sustained spinning.
What is fixation?
Maintaining foveation on a stationary object.
how do you test for smooth pursuit eye movements?
By testing ability to follow a moving target.
How do you test for saccades?
By testing the ability of a stimulus in the peripheral field to make the eyes shift toward it.
How do you test for Vestibular eye movements?
By checking to see if the eyes move against the direction of head rotation (normal), or with it (abnormal).
How do you test for Vergence?
By putting your fingers in front of the nose and moving closer or away.
How do you test for optokinetic eye movements?
By using optokinetic tape to elicit nystagmus
How do you test for Fixation?
Look to see if the patient can maintain a stable gaze.
What are the horizontally acting eye muscles? What is each one's action?
-Medial rectus - adduction
-Lateral rectus - abduction
What are the actions of Superior Rectus?
-Elevation
-Incycloduction
-Adduction
What is incycloduction
Intorsion - rotating the top of the eye toward the nose
What are the actions of Inferior Rectus?
-Depression
-Extorsion
-Adduction
Are the eyeballs sitting in the eye sockets in line with the axis of the socket?
No; they're at a 23' angle off from it.
What does the degree of alignment with the eye socket mean for testing oculomuscles?
You have to align them differently to be testing the pure function of each muscle.
What is the primary action of superior oblique? 2'/3' actions?
1. Intorsion
2. Depression
3. Abduction
What is the primary action of inferior oblique? 2'/3' actions?
1. Extorsion
2. Elevation
3. Abduction
What muscles are you using when you look up and to the right?
SR in the right eye
IO in the left eye
What muscles are you using when you look straight up?
SR/IO in both eyes
What muscles are you using when you look down and to the right?
IR in the right eye
SO in the left eye
pneumonic for looking straight down:
IRSO
in both eyes
What does the superior division of CN III innervate?
-Levator palpebrae
-Superior rectus
What does the inferior division of CN III innervate?
Everything else:
-Medial rectus
-Inferior rectus
-Inferior oblique
-Sphincter pupillae
-Muscularis ciliaris
What does CN IV innervate?
Superior oblique
What does CN VI innervate?
Lateral rectus
What surrounds all the extraocular muscles?
The annulus of zinn
What does Hering's Law say?
If you look to the left, the left lateral rectus and right medial rectus fire equally and at the same time.
What happens if you put your finger on your nose?
Both medial rectus fires fire at the same rate.
What happens if you tilt your head to the left?
-Left eye intorts via SO/SR
-Right eye extorts via IO/IR
How are the eyes contained in the eye sockets?
By orbital pulleys that contain smooth muscle that aids in eye movements and keeps the eyes in a straight forward position.
What are the extraocular muscle pulleys?
Fibroelastic structures that function like the trochlea.
What do the extraocular muscle pulleys function to do?
Fix the position and pulling direction of the rectus muscles.
Where does the global layer of the rectus muscles insert?
On the eyeball
Where does the orbital layer of rectus muscles insert?
On the pulleys
What are the extraocular muscle pulleys made of?
-Elastin
-Collagen
Where are the pulleys in the orbit?
In the anterior orbit
Which cranial nerves pass through the cavernous sinus?
3, 4, V1/2, and VI; and the sympathetic plexus
Where does CN III originate?
In the midbrain tegmentum
What connects the CN III nucleus to the CN VI nucleus?
The MLF
What happens if a lesion disrupts the communication between CN III and CN IV?
INO
What 2 vessels does CN III snake between?
PCA and Scerebellar A
Where is the oculomotor subnucleus for levator palpebrae?
In the midline of the oculomotor nucleus
What is important to know about the superior rectus subnuclei?
They are crossed so innervate the contralateral superior rectus
What will happen if we blow out the whole oculomotor nucleus?
-Contralateral inability to raise eye
-Bilateral ptosis (low lids)
-Ipsilateral everything else
Where is the nucleus for CN IV?
In the DORSAL lower midbrain
If looking at a cross-section of the lower midbrain, what would you see?
-Inferior colliculi (back)
-Sylvian aqueduct (midback)
-Cn IV nuclei
-MLF in front of CN4 nucleus
What is the nucleus for CN 3 situated in front of, looking down at a midbrain crosssection?
Superior colliculi
What cranial nerves pass between PCA and SCA?
3 and 4
Where is HORIZONTAL GAZE organized?
At the pons
What neurons help organize horizontal gaze, and where are they housed?
-Burst neurons
-Omnipause neurons
Housed in the PPRF
What is the PPRF?
Peripontine Reticular Formation
What cranial nerves are connected to the PPRF?
3 and 6
How is CN 3 connected to CN 6?
Via the MLF
What happens to cause horizontal eye movements?
1. Omnipause neurons in PPRF turn off
2. Burst neurons excite motor neurons in CN VI nucleus
3. Half these CN VI motor nerves project to contralateral CN III nucleus via MLF
4. Result is both lateral rectus and medial rectus contraction
What else gives input to CN VI nucleus?
Vestibular nucleus
What is achieved by vestibular input to CN VI nucleus?
the Vestibuloocular reflex during horizontal head rotations
How are the neurons in the PPRF behaving when you AREN'T shifting your gaze?
-Omnipause always on and inhibiting the burst neurons.
What 2 pieces of info does the MLF carry?
-Signals for horizontal gaze from CN 6 to CN 4
-Signals from vestibular nucleus to Interstitial nu of Cajal for vertical gaze
What does the rostral interstitial nucleus of the MLF contain?
Burst neurons for vertical saccades
What is the function of the Interstitial nucleus of Cajal?
Vestibular input on vertical ocular motor neurons allows for VERTICAL GAZE HOLDING.
What is the Nucleus prepositus hypoglossi for?
Horizontal gaze holding
What is in the Posterior commisure?
Crossing fibers for UPGAZE and pupillomotor structures.
So what would result from a unilateral dorsal midbrain lesion or compression of the posterior commissure?
Bilateral inability to look up (tectospinal tract)
2 sites that give supranuclear control of eye movements:
-Cortex
-Vestibular nuclei
If you pour cold water in the right ear what happens?
The left vestibular nucleus will dominate and make you think you're spinning to the left.
What direction will be the
-Slow movement of eyes
-Fast compensatory phase
Slow = to the right
Fast = to the left
What is this called?
Left beating nystagmus
What type of nystagmus will result from pouring warm water in the right ear?
Right beating nystagmus
What does the Frontal Eye field contribute to eye movement?
-Voluntary saccades
-Vergence
-Smooth pursuit
What does the Supplementary eye field contribute to eye movement?
It programs saccades as part of learned or complex behavior.
What is the Dorsolateral prefrontal cortex important for in eye movement?
Programming saccades to REMEMBERED LOCATIONS
What is the Parietal eye field important for in eye movement?
Triggering visually guided saccades to reflexively explore the visual environment.
What is the Posterior parietal cortex important for in eye movement?
Directing visual attention in extrapersonal space
What is the MT important for in eye movement?
Encoding speed and direction of visual stimuli in 3 dimensions
What is the MST important for in eye movement?
Encoding moving visual stimuli
If you have a right sided stroke on which side would you lose smooth pursuit pathways?
On the ipsilateral, same side because the pathway has a double cross.
Purpose of eye movements:
foeation
Horizontal gaze is encoded at the ____ level
Pontine
Vertical gaze is encoded at the ____ level
midbrain
The frontal eye field controls:
Eye movements in the contralateral direction
The MT and MST mediate
Pursuit in the ipsilateral direction