Eye Movements Flashcards
the only cranial nerve that crosses the midline of the brain is:
the trochlear nerve
motor innervation to the muscles of the eye innervated by CNIII arises from the ____ nucleus. Parasympathetic innervation of ciliary muscles arises from the ___ nucleus
motor - occulomotor nucleus
parasympathetic - Edinger-Westphal
CNIII travels in close proximity to which arteries?
posterior communicating & posterior cerebral
Compression of CNIII results in which early characteristic sign? why?
dilation of the pupil due to parasympathetic fibers; travel on outer edges of CNIII therefore more susceptible to compression, less to ischemic damage
Identify five important facts about CNIV:
- innervates superior oblique muscle
- only CN to exit from dorsum of brain
- only CN to cross the midline of the brain innervating contralateral muscle
- long & thin = easily damaged in head trauma
- arises from trochlear nucleus in rostral pons
Identify 4 important facts about CNVI:
- innervates lateral rectus
- arises from abducens nucleus in facial colliculus in caudal pons
- travels in close proximity to internal carotid in the cavernous sinus
4.
describe the firing of extraocular nuclei and saccadic eye movement:
nuclei have tonic activity and then fire in “bursts” followed by a very brief delay before eye movement ensues (allows for accuracy). Saccadic eye movements: rapid movement of eyes (voluntary)
initiation of saccades occurs in:
frontal eye fields & superior colliculus
what are micro saccades?
mini-saccades that occur involuntarily to prevent using same rods for too long, which would result in loss of visual field via adaptation
describe the course of activation of horizontal eye movement, beginning in the right frontal eye field:
this results in movement (away from/toward) the right frontal eye field:
frontal eye field > LEFT paramedian pontine reticular formation & superior colliculus > left abducens nuclei > MLF & left lateral rectus > (MLF > right medial rectus)
movement AWAY from right frontal eye field
describe inputs to the superior colliculus:
what is its function?
visual from retina
sound from inferior colliculus
somatic from spinal cord and cerebral cortex
= map of world, controls head and eye movements in response to stimuli
what is the function of the Paramedian pontine reticular formation:
necessary for voluntary horizontal eye movement (damage > inability to direct gaze towards damaged side)
damage to the MLF between the occulomotor and abducens nuclei results in:
internuclear opthalmalgia: loss of coordination of eye movements - if one eye moves laterally, the other won’t move medially
describe the pathway for activation of vertical eye movement:
diffuse areas of cerebral cortex > rostral interstitial nucleus in midbrain > CN III & IV &VI & posterior commisure (connects RIN to CNIII&IV)
describe “tracking” and its pathway
smooth eye movements to follow moving object. use similar pathway as VOR.
occipital eye field > pontine nuclei > middle cerebellar peduncle > flocculus > inferior cerebellar peduncle > vestibular complex
what is the optikinetic reflex:
involuntary fixation on an object moving in relation to the head (think of watching something out moving car window) . complements VOR & uses same pathway as smooth eye movement. = optokinetic nystagmus. damage > inability to follow object moving towards damaged side of cortex (away from side of vision loss)
what is the fixation reflex:
fixation on moving object
what is vergence?
adjustment of eyes to focus on near (convergence) or distant (divergence) objects. convergence requires pupillary constriction and ciliary muscle contraction
what is the pathway for the pupillary light reflex?
retina > pretectal nuclei> posterior commissure > right & left Edinger-Westphal nuclei
what are the frontal eye fields?
areas of premotor cortex responsible for voluntary horizontal gaze
