Module 8 - The Visual System Flashcards
The extraocular muscles are innervated by 3 different cranial nerves - which nerve innervates the:
- lateral rectus
- superior oblique
- all other eye muscles
- lateral rectus - abducens (CN VI)
- superior oblique - trochlear (CN IV)
- All other eye muscles - oculomotor (CN III)
What is the mnemonic for remembering extraocular eye muscle innervation?
LR6 SO4 - all the rest are 3
Locate the oculomotor nerve (CN III) on this image and micrograph of the brainstem
Locate the trochlear nerve (CN IV) on the below images
Locate the abducens on this image.
Gaze refers to?
The coordinated movements of the right and left eyes to a visual target
In order to coordinate synergistic eye movements, the nuclei of cranial nerves III, IV, and VI need to communicate with one another both ipsilaterally and contralaterally. How does communication between these nuclei occur?
Via the ascending medial medial longitudinal fasciculus (MLF)
What is the ascending MLF critical for?
Coordinated eye movements
On this midbrain micrograph, locate the oculomotor nerve and the medial longitudinal fasciculus.
On this rostral pons micrograph, locate the trochlear nerve roots and the ascending MLF
On this caudal pons pons micrograph, locate the abducens nuclei and the ascending MLF
Coordinated horizontal and vertical movement of both eyes is facilitated by gaze centers in the brainstem. Where is the:
- vertical gaze center
- horizontal gaze center
What are saccades?
Rapid simultaneous movements of the eyes that redirect the gaze between different fixation points
What are the two major types of saccades?
Reflexive saccades
Volitional saccades
What is a reflexive saccade?
Visually guided saccade in response to external cues
What is a reflexive saccade?
Visually guided saccade in response to external cues
What is a volitional saccade?
Voluntary eye movements, independent of any visual stimulus
Saccadic eye movements can be initiated by X or Y areas of the brain.
cortical
subcortical
Where does cortical initiation of saccades occur?
Frontal Eye Fields - located in the supplementary motor area and extend anteriorly
What kind of saccades are primarily initiated by the frontal eye fields?
Volitional saccades
On this image of the cortex, where are the frontal eye fields?
Saccadic eye movements can be initiated by cortical or subcortical areas of the brain. What is the main subcortical initiation of saccades?
The superior colliculi
What is the main input for reflexive saccades?
The superior colliculi
Just like the ascending medial longitudinal fasciculus (MLF), the descending MLF allows for communication between nuclei in the brainstem. Of what is it comprised?
The medial and lateral vestibulospinal tracts
From what does the descending MLF arise? What does it influence?
Vestibular nuclei
Influences muscle tone for balance and posture - it is also critical for positioning of the head and neck
What is the function of smooth pursuit?
To track slowly moving objects in the environment
In smooth pursuit, eye movements are coordinated so that the projection of the moving visual target is stabilized on the retina. This requires integration of information from which three brain areas?
- visual cortex and frontal eye fields
- cerebellum
- vestibular nuclei
What is the role of the visual cortex and frontal eye fields in vision?
“See” and “initiate eye movements”
What is the role of the cerebellum in vision?
My movement in the environment
What is the role of the vestibular nuclei in vision?
Where my body is in the environment
Vestibulo-ocular reflex
The vestibulo-ocular reflex (VOR) involves rapid adjustment of eye movement in response to movement of the head
On this image, identify the three blobs.
What is cranial nerve III?
Oculomotor
What is cranial nerve IV?
Trochlear
What is cranial nerve VI?
abducens
In order to function efficiently, the eyes must be able to adapt rapidly to changes in the visual environment (e.g., changes in lighting/distance). What are the names of the 4 eye reflexes?
- pupillary light reflex
- pupillodilator reflex
- corneal blink reflex
- accommodation
On this ventral/inferior surface of the brain, locate the:
- optic nerves
- optic chiasm
- optic tracts
- lateral geniculate nuclear
- midbrain (red nuclei, oculomotor nuclei, edinger-westphal nuclei)
The eyes must frequently adjust to changes in lighting conditions (i.e., bright vs dark) which involves intact function of which nervous system?
The parasympathetic nervous system
Which reflex allows for the eyes to adjust to changing light conditions?
The pupillary light reflex
In response to increased brightness in the visual environment, the constrictor pupillae muscles in the iris contract and cause the pupil to shrink (meaning less light reaches the retina)
What does the pupillodilator reflex involve?
Dilation of the pupil, usually in response to sensory or emotional stimuli
Which nervous system does the pupillodilator reflex rely on?
The sympathetic nervous system.
In response to a strong emotional state the dilator pupillae muscles in the iris contract and cause the pupil to enlarge
What is the corneal blink reflex?
When the cornea of the eye senses touch or pain, a reflex pathway is initiated that results in both eyes blinking.
This corneal blink reflex is a protective response to prevent any foreign material from damaging the eye.
What is disconjugate gaze?
Refers to movement of the eyes in opposite directions (e.g., crossing your eyes)
What are the two types of disconjugate gaze?
Convergence and divergence
When does the accommodation reflex occur?
When we focus on a near object
When we use the accommodation reflex to focus on a near object, several different events must occur simultaneously. What are they?
- convergence of the eyes (to maintain singular binocular vision of a near object
- thickening of the lens
- constriction of the pupil (to sharpen the image by increasing the depth of focus)
What is responsible for coordinating the three events needed for the accommodation reflex to occur?
The supraoculomotor area in the rostral midbrain
