Eye Movements and Sensorimotor Integration Flashcards
If you cannot move your eyes?
Really inhibits your ability to visually perceive things
Stabilized retinal images: make sure the image always falls on exactly the same parts of the retina
Stabilized images rapidly disappear
Cannot see it anymore
Even when you are staring at a stationary image, your eyes are making slight movements, just fractions of a degree, to keep the image “fresh”
Three Antagonistic Pairs of Muscles (name them)
- Lateral and medial rectus muscles - Horizontal movements
- Superior and inferior rectus muscles (both CN III)
- Superior (trochlear, CN IV) and inferior oblique muscles (CN III)
Medial rectus:
Medial rectus: adduction (toward the nose); controlled by oculomotor nerve (CNIII)
Lateral rectus:
- direction of movement
- innervated by
abduction (away from the nose); controlled by abducens nerve (CNVI)
Superior and inferior rectus muscles
(both CN III)
*When eyes are abducted- rectus muscles are primary eye movers
Oculomotor nerve (CN III) -in addition to the muscles of the eyes... innervates
also innervates the levator muscles of the eyelid and has parasympathetic function to help control pupillary constriction (Edinger-Westphal nucleus)
-controls 4 of the eye muscles
Types of Eye Movements and Their Functions
5 basic eye movements grouped into two categories
*Those that SHIFT the direction of gaze Important for foveation Movements: vergence movements *Those that STABILIZE the gaze -Help maintain foveation while the head is moving
Movements: Vergence, saccades, smooth pursuit movements, and vestibulo-ocular and optokinetic movements
*Eye Movements that SHIFT the direction of gaze
-Important for foveation
Movements: vergence movements
*Eye movemnts that STABILIZE the gaze
*Help maintain foveation while the head is moving
Movements: saccades, smooth pursuit movements, and vestibulo-ocular and optokinetic movements
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5 movements of the eyes
Vergence Movements Saccades Smooth Pursuit Movements Vestibulo-ocular Optokinetic Eye Movements
Vergence Movements
-when required
Align the fovea of each eye with targets located at different distances
Required to track a target that is moving closer or further away
Commonly used with abruptly shifting the direction of gaze from a near object to a far object
*These movements are disconjugate/disjunctive, meaning that the eyes do not have to move in the same direction
Saccades
- voluntary and/or reflexively
- need a target (t or f)
*Can be elicited voluntarily, but also occur reflexively
*Have a target for a saccade
It moves
It takes a brief amount of time for the eyes to move to align with the target and initiate another saccade (have to set up a new motor command to move the eyes)
*If the target moves during this delay, the new saccade will miss the target and another one has to be initiated (new motor command)
see graph slide 12
Smooth Pursuit Movements
- when used?
- reflex or voluntarily?
- Slower tracking movements of the eyes
- Designed to keep a moving stimulus on the fovea once foveation has been achieved
- Under voluntary control in that you can choose to track something or not
Saccade + Smooth Pursuit
for tracking
- Saccade to foveate target (to catch up) and then smooth pursuit movements to track it (track with it, no longer require saccades)
- Smooth pursuit movements match velocity of target (Speed and target)
slide 14: Eye movements = blue
Target= red
Vestibulo-ocular and Optokinetic Eye Movements
- Work together to move the eyes and stabilize the gaze relative to the external world and compensating for head movements
- Reflexive responses
- Keep images from slipping on the surface of the retina as head position varies
Vestibulo-ocular:
-limitations
*stare at something and move your head back and forth. *Eyes automatically move to help maintain gaze
*Detects changes in head position and produces corrective eye movements
(as head moves can continue to see what you are looking at)
*Limitations: speed (insensitive to slow movements) and persistent rotations of the head
Optokinetic system:
- similar to Vestibulo-ocular, but is very sensitive to slow movements of large areas of the visual field
- Head movements slow, vestibular info declines, and optokinetic system fine with that and will prevent the image from slipping across the retina
Eye Movements: Key to Neurological Exams
(Eye movements are a super important part of neurological examinations)
-they can test or check or challenge 3 things i think)
*They test the function of several CNs (II, III, IV, VI)
*Also challenge circuits that span most of the CNS (except spinal cord mostly)
*Check voluntary and involuntary aspects of eye movement
Learn more on Page 453
Neural Control of Saccadic Movements
Moving the eyes to fixate on a target in space requires two things:
Control the amplitude (how far) of movement
Control the direction of movement
AMPLITUDE: is one of the two things required to move the eyes to fixate on a target
(Neural Control of Saccadic Movements)
encoded by duration of neuronal activity in the lower motor neurons
After each saccade, reestablish baseline activity to hold the eye steady
DIRECTION: is one of the two things required to move the eyes to fixate on a target
(Neural Control of Saccadic Movements)
- is determined by which eye muscles are activated
- Not easy to separately control each muscle independently
- Controlled by local circuit neurons in two gaze centers
Gaze Centers
- location
- name them
- Located in the reticular formation
- Paramedian pontine reticular formation (PPRF)
- Rostral interstitial nucleus/mesencephalic reticular formation
- Activation of each gaze center separately results in eye movements along that single axis
- Activation in concert results in oblique movements (not oblique muscle action, per se)
*Paramedian pontine reticular formation (PPRF):
function
- horizontal gaze center
- Collection of local circuit neurons near the midline of the pons
*Rostral interstitial nucleus/mesencephalic reticular formation:
- Rostral interstitial nucleus/mesencephalic reticular formation: vertical gaze center
- Collection of local circuit neurons in the rostral part of the midbrain reticular formation
PPRF
(horizontal gaze center)
- Works with oculomotor and abducens nuclei to generate a horizontal saccade (Example- saccade to the right)
- Neurons of the PPRF innervate neurons in the abducens nucleus on both sides of the brain
- Two types of cells: lower motor neurons (that innervate the lateral rectus muscle on same side) and internuclear neurons that send their axons across the midline
- Axons of the internuclear neurons ascend in the medial longitudinal fasciculus and terminate in the portion of the OCULOMOTOR NUCLEUS that contains lower motor neurons that control the medial rectus muscle
- Activation of PPRF neurons on the right side –> horizontal movements in both eyes to the right
- Also send axons to the medullary reticular formation
- Contact inhibitory local circuit neurons, which project to the contralateral abducens nucleus on lower motor neurons and internuclear neurons
- These connections serve to reduce activity that would move the eye in the wrong direction
Where is the sensory part of sensorimotor coming in?
(how does sensory information get incorporated***)
-main players
*Have to figure out what is a salient target and where it is in space : This comes primarily from the visual system (but not limited to this)
- Superior Colliculus (aka optic tectum in non-mammalian vertebrates):
- Assorted areas of the frontal and parietal cortices, including the FRONTAL EYE FIELDS (in frontal lobe rostral to premotor cortex)
- The sensory map is in line with the motor map
- Sensory info comes in and leads to activation of neighboring upper motor neurons that will move the eye an appropriate amount to align the fovea to the target
