Brainstem and CN III, IV, VI Flashcards
abducens nerve
lateral rectus
trochlear nerve
superior oblique
oculomotor nerve
medial rectus
superior rectus
inferior rectus
inferior oblique
axons of VII
loop around nucleus for CN VI (abducens)
CN VI exits skull
superior orbital fissure
CN VI innervates
ipsilateral lateral rectus
lesion to abducens
ipsilateral loss of lateral rectus
ALSO:
facial motor nuclei has bend around the abducens
-therefore, ipsilateral facial nerve deficits
trochlear nerve
axons exit dorsal
**only one doing this
-LMNs decussate**
do trochlear nerve decussate
yes
LMN do decussate
trochlear nerve innervation
contralateral superior oblique mm.
oculomotor
extraocular mm
levator palpebrae superioris
PS supply to iris and ciliary mm
pupil constriction
parasympathetic
protect from light AND increase acuity
pupil dilation
sympathetic
course of oculomotor nerve
goes out interpeduncular fossa
IPSILATERAL
interpeduncular fossa nerve
oculomotor
edinger westphal nucleus
preganglionic PS
-terminate in ciliary ganglion
pupil reflex
afferent - CN II to bilateral pretectal nuclei
posterior commisure to edinger westphal
efferent - CN III out to pupillary sphincter
why do we need an accurate visual system
- phototransduction slow
- fovea is small
need to foveate objects
-keep them from moving across too quickly
-also, have binocular, so need to coordinate both eyes together
alignment of eyes requires
- move both eyes same direction (conjugate)
- move objects opposite direction (vergence)
conjugate movement
eyes same direction
vergence movement
eyes opposite direction
voluntary movements involve?
UMNs - in cortex
-to basal ganglia and cerebellum
LMNs - to CN III, IV, VI
-no direct corticobulbar innervation
systems that keep object on fovea
1 saccades
2 smooth pursuit
3 vergence
systems that stabilize retinal image
1 vestibuloocular movement
2 optokinetic movements
saccades
fast, redirect gaze
smooth pursuit
keep object on fovea
-requires a visual target
what requires visual target
smooth pursuit
conjugate movements
saccads
smooth pursuit
fast phase of nystagmus
saccades
-redirect gaze
CNS ignores input?
during a saccade
frontal eye fields
BA 6 and 8
- contralateral to paramedian pontine reticular formation (PPRF)
- also to rostral interstitial nucleus of the MLF
- also to superior colliculus
rapid horizontal gaze
PPRF
- to ipsi abducens
- to contra oculomotor
rapid vertical gaze
to riMLF
-bilateral
input to frontal eye field
supplementary motor
parietal eye field
superior colliculus
visual grasp reflex
location of frontal eye field
anterior to facial of primary motor cortex
something moving in periphery
parietal eye field to frontal eye field
supplementary eye field
looking at sequence
-like down totem pole
PPRF projections
to CN III, IV, VI
via MLF
left cortex
controls rightward gaze
and vice versa
saccades
smooth pursuit
requires visual target
- keep target on fovea
- calculates vector (speed and direction)
slower
use of flocculus
smooth pursuit
-uses cerebellum
smooth pursuit circuit
FEF > pontine nuclei > flocculus > vestibular nuclei > MLF > motor nuclei of III, IV, VI
difference between smooth pursuit and VOR
the afferent info
smooth pursuit - visual target
VOR - vestibular apparatus about acceleration
convergence
eyes toward midline
-medial rectus mm.
stimulus for convergence
retinal disparity (objects out of focus)
too close - converge
close object
loss of focus
- drives accommodation
- CN III
also - pupillary constriction occurs
-increasing acuity
occurs during convergence
accommodation of lens
pupillary constriction
near triad
convergence
accommodation
pupil constriction
circuits of vergence
FEF to reticular formation in rostral midbrain
adjacent to CN III
VOR
move eye in response to acceleration
optokinetic system
active during continuous velocity
-with no acceleration
REFLEXIVE
what are optokinetic movement
oscillatory eye movement in response to steady velocity
smooth pursuit alternating with saccades
watching a train passing
optokinetic movement
circuit to optokinetic
motion sensitive ganglion cells > accessory optic nuclei > vestibular nuclei > MLF > motor nuclei of III, IV, VI